Exhaust Leak Cause Lean Condition

1 and getting a lean condition. Excessive oxygen readings in the exhaust will set lean codes. I've also had an exhaust smell in the cabin, on colder days I would just switch on recirculate and the windows would be closed, didn't really seem to get in the car that way. However, a vacuum leak such as rotted or loose vac hoses can also cause issues, but you usually get a check engine and the dreaded high idels response. There also could be some other reasons, but the air flow sensor and vacuum leaks are the most common. Exhaust leaking before it exits the system will result in a lower back pressure, which in turn may cause the bike to run hot. Lean Fuel Mixture - Any condition which will cause unmetered air to enter the intake manifold, and ultimately the combustion chambers, will cause high hydrocarbons (HC). So the air could make its way back a few inches to the exhaust valve. * Vacuum or crankcase leaks can cause a lean condition and/or possibly a high idle. If the ECT was the cause of your rich condition, you would see grossly inaccurate readings while viewing sensor data with a scan tool. The codes: P0171 - Bank 1 too lean. Check also for cold exhaust leaks. Can an injector leak on the return side cause a lean condition and will an LB7 go into limp mode like an LLY if the leak is bad enough I'm just trying to convince myself the truck will be fine till Monday:badidea: Any input would be appreciated. And always check for after- market modifications. ’ When an engine runs rich, it burns fuel slowly, causing the extra air to forcefully burn the unburned fuel and spit out when the exhaust valve opens. If you don't have a scan tool, you can visually inspect under the hood for leaks. The most common cause is the crush washer seal in the exhaust port of the cylinder. A lean exhaust condition, not faulty oxygen sensors, is at the root of the problem. Re: Exhaust leak causing a miss? « Reply #24 on: Dec 05, 2010, 10:29:44 AM » weak ignition could cause lean condition i would suggest you get a hayne manual has all info on testing your sensors and ignition componets. A third sign your exhaust may be leaking is if your gas pedal vibrates while you are driving. Ford Expedition lean codes could caused by a leaky PCV hose. The allowance of unchecked incoming atmoshere to the exhaust will allow excessive reversion/shock wave to traverse the entire path of mix all the way to the air cleaner and lean the mix. A lean fuel mixture would not cause a sulfur smell. This will also require a scan tool. Most Common Causes Of P0171, P0174 DTC's. It will cause a clogging up off the catalyst resulting in the degradation of the honeycomb in it. A head gasket leak or cracked head will allow the coolant to be burned. a vac leak will allow in unletered air which causes a lean condition not a reich one, the AIV's (Air Inlet Valves) in the finders that go into the exhaust have nothing to so woth how the car runs, they simpley allow air into the exhaust to help the second set of cats do their jpobs, they are essentially useless andnissan quit using them after a. There are many other causes, a leak in the intake, leak in exhaust before the O2 sensors, cracked or disconnected vacuum hoses, fuel regulator, fuel pump, clogged fuel lines etc. just recently the light has came on , and is staying on. exhaust side. The other reasons your car can leak water are condensation from the air conditioning or the exhaust, neither of which are any cause for alarm. Below are some tips and tricks to diagnose the most common faults /defects / failures /malfunctions that cause lean air/fuel mixtures that result in high positive fuel trim values- Small vacuum leaks; if both the short and long terms fuel trim values are higher than about 10% with the engine at idle, increase the engine speed to about 2000 RPM. If any of this is wrong, Fish will set me straight, exponentionally:biggrin:. There are lots of faults that can cause rich and lean conditions, but not so erratically. Normally, the sensor will switch back and forth between under. Deceptive Oxygen Sensor Codes. Customer may also complain of rough idle, surging under light throttle, ignition misfire etc. The additional fuel will/can cause the catalytic converters to fail and breakup. Preforming a plug chop is a good way to find out if your engine is running too lean, as you will see a powdery white residue on your spark plug in the presence of a lean condition. Step 5: Check for Vacuum Leaks. Beyond the potential of the engine running too lean, the other thing would be if any change in sound is bothersome to you. (But it was running great) a bit of a dead spot between 5200 and 5800 RPM. I have checked all vacuum lines, sprayed carb cleaner around MAP sensor, Intake manifold gaskets, between throttle body and manifold and around all vacuum points. Code 45 indicates exhaust O2 rich. Vacuum or crankcase leaks can cause a lean condition. during the combustion process. In normal operation the ECM delivers less fuel and advances spark when EGR comes in. I triple checked before making any tuning changes. You may also have a carb issue with lean. Does an exhaust leak create a lean or rich condition? What effect does this have on catalyst efficiency? www. A leaky EGR valve can act like a vacuum leak and cause a lean misfire at idle. Gray or Blue Smoke from Diesel Exhaust. Since all the fuel/air mixture passes by these gaskets, any leak at all can cause a serious lean condition. The additional fuel will/can cause the catalytic converters to fail and breakup. Ford TSB 04-17-4 details procedures for checking fuel trim and looking for vacuum leaks. I can smell a very faint exhaust smell if I'm leaning over the engine with the hood up,. Those codes do NOT mean the O2 sensors are bad, it means a lean condition has been detected. Check intake vacuum at idle, and inspect vacuum hose connections. A vehicle has set DTC P0172, indicating a lean exhaust and a vacuum leak is suspected. Exhaust leaks, especially near the sensor can pull in air and cause a false lean reading. 1 and getting a lean condition. But you said those are the only two things that can cause a tailpipe backfire. Ford Expedition lean codes could caused by a leaky PCV hose. In many instances this code sets if there is a problem with the fuel system, a vacuum leak, an exhaust leak, or other problem with the engine resulting in it running leaner than normal exists. Running too lean – High positive fuel corrections can be traced to MAF and O2 sensor faults,. If the left side fuel trim is significantly higher than the right- i would suggest you take a closer look for either an exhaust of intake leak. Higher than normal exhaust temperatures can also lead to catalytic converter meltdown. symptoms it has now is smell of fuel (mostly around tailpipe) and significant drop in mpg ( from 17/20 to 5/8 ). Rich Mixture. It could be as easy as a small vacuum hose broken. A lean condition may be present during high fuel demand due to a fuel pump that does not deliver enough fuel, a plugged fuel filter, or a restricted fuel pipe. To eliminate your intake leaks, simply attach this Intake Leak Pressure Tester to your turbo inlet and apply compressed air through the standard tire. To determine if the lean condition is the result of a vacuum leak, bring the engine up to about 2,000 RPM. P0430 - Catalyst efficiency below threshold. Inaccurate Engine Timing. A (false) lean condition is reported to the PCM, which then increases fuel delivery to that bank of cylinders. The computer is always tryin to adjust the air fuel ratio to 14. Replied by juergen. Vacuum leaks generally cause hesitation or inconsistent component operation (ie, idle valve). ), but the blown head gasket can also cause the engine to overheat. Could it be so that case center gasket starts to leak only when engine is hot or under load? Could carbonized exhaust cause lean condition for the engine?(expansion chamber should be clean and silencer wools are recently changed) Im starting to get desperated cos there is no good reason for the engine to run so lean. An exhaust system leak that may not be audible but can set this code. A catalyst can not clean up CO and HC unless there is enough oxygen in the exhaust. Replaced with new headers. Water contamination will cause a lean condition. Too rich and the catalyst can melt down. A very hot exhaust will heat up the front 02 depending where it is and skew its reading, pretty sure in the lean direction. But after 2-4 starts and. It is going to cost me about $500. In this video I will show you how to use freeze frame data and fuel trim numbers to identify a vacuum leak. So, An oxygen sensor failure can lead to incorrect readings of exhaust gasses. I also had a slight hesitation when cruising at around that rpm then feathering the gas. Back-firing is through the carbs and can be timing related, cam related or rich mix related, among other things. To compensate for the lean condition the engine controller signals the injectors to add more fuel in an effort to. – Dirty air filter. However this occurs only on cylinders with bridged exhaust ports. Something like a leaking injector oring, leaking air distribution manifold oring, or etc that is specific to bank 1. Any sensor can. GM, in all its infinite wisdom, uses plastic and rubber gaskets for the intake manifold and plenum gaskets. "Ultimately, a simple air leak can cause a lean condition that will cause an excess of temperature in the exhaust system, which can cause a thermal event, rendering the DPF inoperable and. Bank 1 and Bank 2 Lean?? the manual says an exhaust leak could cause it. The material in the cats can then be ingested back into the cylinders and eventually cause engine failure. The cheapest part to throw at it is the O2 Sensor. Sorry if I wasn't clear. Most Common Causes Of P0171, P0174 DTC's. Sometimes a small leak will make a ticking noise depending on where it's at. Again in theory, when something like this happens, the ECU would get a rich reading from the o2 sensor and start pulling fuel which would then cause a lean condition. A very hot exhaust will heat up the front 02 depending where it is and skew its reading, pretty sure in the lean direction. Does an exhaust leak create a lean or rich condition? What effect does this have on catalyst efficiency? www. O2 Sensor Signal Stuck Lean Bank 2 Sensor 1 What the P2197 code means This code is usually an indicator of an O2 (oxygen) sensor problem, although there are several things that can cause an O2. Code 44 Lean Exhaust '88 K1500 5. When STFT hits its limit (-25%), the HO 2 S finally drops, and is then stuck lean until STFT is able to climb back up to normal levels. Test for Exhaust Leak. Air leaks are, by far, the number one cause of vintage engine piston seizures. The main causes for this problem are too quick warm-up, too lean carb jetting (main jet), or too hot of a spark plug range. P013A-O2 SENSOR 1/2 SLOW RESPONSE - RICH TO LEAN. If the rpm change you may have a leak, also keep something around in case of fire. I've cleaned the MAF s. If the lean codes keep coming back, the MAF sensor may have to be replaced if the engine does not have a vacuum leak or fuel delivery problem. The third and final common cause for this P0171 lean code on this Corolla with a 4 cylinder 1ZZ-FE 1. Your bank one oxygen sensor is the first downstream sensor. The O2 sensors read/ send signals depending on the amount of "unburnt" air, so if air is being sucked in the exhaust the truck will keep adding fuel trying to fix the false signal that. 5 volts (lean signal) and over. I found a small exhaust leak at the header collector/Y-pipe joint, shown in picture below. The ECM interprets “lean” when the HO2S voltage is below 0. A catalyst can not clean up CO and HC unless there is enough oxygen in the exhaust. But if its only one cylinder, I really can't say how that would affect your o2 readings. the other 2 mounts are not really. A third sign your exhaust may be leaking is if your gas pedal vibrates while you are driving. this will produce steam and free Ox that the O2 will pick up on. Vacuum or crankcase ventilation system leaks can cause a lean condition or possibly a high idle. VACUUM LEAKS. Another common problem of this type is a single point seizure on the center of the exhaust side of the piston. Exhaust leaks before or near the HO2Ss (exhaust manifold gasket, mating gaskets, etc. This will cause a "Lean Misfire" condition in the engine. Code 44 Lean Exhaust '88 K1500 5. Theory of Operation. To remedy. Would an intake leak effect just 1 jug? No exhaust leak in smoke test. 0 Mustang Tech: 2: Sep 3, 2007: Exhaust Leak Cause Rich or Lean Condition: 1994 - 1995 Specific Tech: 7: Dec 20, 2006: Back. So if 100% that int and exh sensors are good and correct then recheck pipes and tubes near throttle body like the evap solenoid circuit. A third sign your exhaust may be leaking is if your gas pedal vibrates while you are driving. Newer, low mileage truck owners can skip this paragraph, but many of us like to have a worn out beater truck laying around, or maybe your teenager bought their first car from a not-so-honest guy. Another common problem of this type is a single point seizure on the center of the exhaust side of the piston. A lean condition may be present during high fuel demand due to a fuel pump that does not deliver enough fuel, a plugged fuel filter, or a restricted fuel pipe. Calculated Load = Current Air Mass X Atmospheric Pressure @ sea level. Damaged/malfunctioning secondary air injection system (mechanically stuck valve). Damage to Other Car Parts. the best way i find exhaust leaks and see how severe they are is by seafoaming the engine through the brake booster vac line. The third and final common cause for this P0171 lean code on this Corolla with a 4 cylinder 1ZZ-FE 1. Fuel pressure might be nice but have the injectors been cleaned. As far as the popping/backfiring goes, I understand it can be caused by a rich OR a lean condition, among other things. The low pressure portion of the exhaust pulse will draw outside air in. Do you no if a lean bank code always displays the same. ), but the blown head gasket can also cause the engine to overheat. What would cause popping through exhaust? Reving my motor steady at around 2400 rpm or cruising I get an intermit slight popping sound out of the exhaust. If no changes have been made to the bike, and it previously ran well, a lean mixture can sometimes be a leaking intake or exhaust gasket. A head gasket leak or cracked head will allow the coolant to be burned. Readjusted valves checked for vacuum leaks with carb spray around intake. Problem CONDITION POSSIBLE CAUSE CORRECTION 7) Idle cut-off solenoid not working. Once a head gasket has failed it can cause all manner of problems, including: 1) Overheating. J Re: Lean codes on bank 1. A vacuum leak and exhaust leak. High fuel pressure can. These bikes are relatively sophisticated and changes to exhaust or intake are a sticky wicket without proper ECU compensations. * Exhaust leaks - If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust and past the sensor. So, An oxygen sensor failure can lead to incorrect readings of exhaust gasses. Codes P0171 & P0174 (Too lean bank 1 & Too lean bank 2) 13 Answers. just swapping a slip-on pipe for another one wont/shouldnt cause a lean condition. The P0171 is one of the more common trouble codes. A leaking exhaust manifold will cause the AFR sensors to read a lean condition, and that in turn tells the ECU to inject more fuel. But in some cases an O2 sensor going bad CAN cause this code. They said after the car passed diagnosis except for the lean conditions, and told me they found an bad manifold gaskets. An exhaust leak upstream of the O2 is kind of unlikely to cause a p0171, as it would have to be siphoning 'clean' air in via venturi effect. An air leak after the lambda sensor, i. Contrary to popular belief, the exhaust has pulses in it from the valves opening, and will actually draw in outside air. Another common problem of this type is a single point seizure on the center of the exhaust side of the piston. Together with the unburned fuel in the exhaust system and an open exhaust, the sparking results in the. Vacuum leaks, torn intake boots, compromised gaskets, or even just the intake manifold bolts are loose are all possibilities. Basically this means that an oxygen sensor in bank 1 has detected a lean condition (too much oxygen in the exhaust). The exhaust seals are usually good for 2-3 times usage. An oxygen sensor failure can lead to incorrect readings of exhaust gasses. A bad vacuum leak in the intake may also cause a lower vacuum. If a car has a check engine light on and has P0171 and P0174 codes stored, the most likely cause is a vacuum leak. You can probably reuse them if they are in good condition. A leak at the exhaust flange is worse. There also could be some other reasons, but the air flow sensor and vacuum leaks are the most common. 7:1 it is considered running lean. At its worst, long-term driving with a vacuum leak, elevated temperatures generated by running a lean air-fuel ratio could result in engine damage. Another common problem of this type is a single point seizure on the center of the exhaust side of the piston. Fuel pressure and intake/exhaust gaskets are the first place I'd look. A blocked EGR valve can cause combustion temperatures to rise, creating a lean condition and raising exhaust temperature. I had a 'tapping' sound (sounded a lot like loose valves) that was progressively getting worse prior to changing plugs. The additional fuel will/can cause the catalytic converters to fail and breakup. High fuel pressure can. Dec 31, 2012 #7. Discovered a poorly done exhaust manifold gasket job, but no indication of leaks (they broke studs, tapped in aftermarket bolts in places). Our Universal, Direct-fit, CARB, High Performance and Diesel converter lines cover over 100,000 applications, including OBDII coverage for all 50 states and are certified in 58 countries around the world. Long answer: Most people don't realize that an exhaust will blow out gasses, and suck in air at different times of the engines run cycle. Intake and exhaust valve timing and leaks are also relatively rare. Also, a leaking exhaust manifold can cause a lean condition or rich condition which causes driveablity symptoms such as running rough. Exhaust leaks can cause O2 sensors to read lean. Eastern Catalytic manufactures catalytic converters, manifold converters and converter components for aftermarket and OEMs. Take a look around and see if you can find the vacuum leak. Does your exhaust smell like gas? Thanks for all the info I will check it out. Re: Lean Runaway Condition After Carb Rebuild I left the intake manifold in place when I did the leak down test. "Ultimately, a simple air leak can cause a lean condition that will cause an excess of temperature in the exhaust system, which can cause a thermal event, rendering the DPF inoperable and. Leaks, no matter where the leak itself is located, will lead to a lean condition (if not recognized) and eventually to exhaust side scoring. Damage to Other Car Parts. One example: a very simple and common problem is dislocated or pinched intake runner-to-cylinder head o-rings. S to switch lean. This is especially true for direct injection vehicles with the lean air/fuel ratios. Lean burn refers to the use of lean mixtures in an internal combustion engine. A vacuum leak creates a lean condition, which can cause serious internal damage. Avoid long periods of idling as this can cause discoloration. Injector seals are called O rings. Then the oxygen content in the exhaust drops (because it is being used up in the combustion process), and the voltage increases (rich condition) and the process repeats, for as long as the car is running, hundreds of times a minute. There appears to be a slight exhaust leak at the exhaust manifold. * Vacuum or crankcase leaks can cause a lean condition and/or possibly a high idle. I took the exhaust off of it to clean some things and noticed it doesn’t have an exhaust gasket. Typically as the O2 sensor deteriorates it produces less voltage, less voltage also indicates more oxygen, thus the computer compensates by adding fuel-> fuel economy goes down. This fault is both common and a clear indication of a sticky HO 2 S. When your engine light comes on because of a weakness or failure in this system, you most likely won’t notice the car driving any differently. Could the exhaust leaking right at the head pipe cause a lean condition?. RE: Running Lean and "Melting Pistons" obanion (Automotive) 7 Sep 04 19:08 HCCI, because of the nearly instant ignition across the entire air/fuel mix, causes a VERY rapid heat and pressure rise, compared to spark ignition. Normally the piston temperature is higher on the exhaust side so catastrophic problems will appear there first. P0171 Lean condition. EGR valve tube/gasket leak; EVR solenoid vacuum leak; Secondary Air Injection. Loosely connected or leaked vacuum lines and hoses can cause a vehicle to run rich. This is a serious problem because this can cause warpage or cracking of the exhaust manifolds resulting, in exhaust leaks. If there is too much fuel mixed with the air, the engine will have a rich condition. Lean burn refers to the use of lean mixtures in an internal combustion engine. Now, I have never heard an exhaust leak sound like detonation (if this isn't detonation, then it could fool almost anyone, I promise!) but I guess it makes sense; (or not enough fuel, or anything like that that could cause detonation) then it would cause a lean condition THROUGHOUT all of the cylinders and thus show up on the wideband as a. If long-term fuel trim (LTFT) for bank 1 is 25% at idle, but corrects to 4% at 1,500 and 2,500 rpm, focus on factors that cause a lean condition at idle, such as a vacuum leak. Bikes with CV style carburetors may be self adjusting to atmospheric pressures. You mentioned an exhaust leak. A lot of the above is good info, but nobody mentioned to you that a leak in your exhaust, either at the head or the muffler clamps could becausing your popping. I had a lean running condition with it once that turned out to be a leaking EGR valve. When STFT hits its limit (-25%), the HO 2 S finally drops, and is then stuck lean until STFT is able to climb back up to normal levels. Common on this truck. Blue smoke is coming from my exhaust This is a definite indication that this engine is burning oil. The only way an exhaust leak can cause a rough idle is if the leak was in a place where it could enter the air intake system. So, what does the code P0171 mean? The symptoms and causes will help you determine the exact issue and how to fix it. GM likes to keep us confused. Even the smallest of leaks can cause the vehicle to vibrate, yet the bigger the leak the stronger the vibrations will be. Check out all the maintenance parts available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. Here are the most common ones. This could result in fuel trim problems and a check engine light, possibly with Fuel System Rich DTCs, such as P0172 or P0175. When this occurs, unburned oxygen enters the exhaust and makes the O2 sensor read lean. 02 Wrangler Napa high milage 10w40 It would cause a lean condition. a vac leak will allow in unletered air which causes a lean condition not a reich one, the AIV's (Air Inlet Valves) in the finders that go into the exhaust have nothing to so woth how the car runs, they simpley allow air into the exhaust to help the second set of cats do their jpobs, they are essentially useless andnissan quit using them after a. An exhaust leak near the upstream sensor can cause the downstream sensor to read a steady lean condition. My 700 sportsman had a small leak and would glow red after a short ride. Backfire is caused by combustion in the intake manifold. Long answer: Most people don't realize that an exhaust will blow out gasses, and suck in air at different times of the engines run cycle. 7 TBI C/K Car Forums. see if you have a leak from the manifold or downpipe. Here are the most common ones. Another cause of misfiring is a weak fuel injector a condition that is referred to as “lean misfire” and occurs because there is no enough fuel in the combustion chamber. P0430 - Catalyst efficiency below threshold. Probable Cause; P0171: Fuel trim (FT) system too lean, bank 1: Intake/exhaust leak, AIR system, MAFNAF sensor, fuel pressure/pump, injector(s), HO2S If the engine is in good condition, and there are no exhaust leaks, engine vacuum leaks, or misfires present, all sensors are working as designed, and all oxygen sensors and catalytic converter. All the gaskets and seals tested out OK right up to the base of the carb. It went on to say this was why when people changed to open headers or increased the size of the exhaust pipe over stock suddenly people were burning valves inside the motor and it would cause a lean condition that people would compensate for by using a larger carb or jetting up. An internal leak in the cooling system would allow coolant to enter the exhaust system and poison the catalytic converter. Pressure test. When in "closed loop," the ECU can detect a lean, or rich, condition and add/subtract fuel to compensate, bringing the observed AFR back in line. The gas in the exhaust pipe can move back and forth in both directions even though there's a net flow outward. As far as the popping/backfiring goes, I understand it can be caused by a rich OR a lean condition, among other things. Conclusion:. There are many things that can cause these trouble codes on the Cadillac Escalade. More serious turbocharger damage or problems with intercoolers are not. This is intended for one use only. This will cause a "Lean Misfire" condition in the engine. Avoid long periods of idling as this can cause discoloration. See this all the time and this will cause a lean mixture if runners are not being actuated by the electric motor. Something like a leaking injector oring, leaking air distribution manifold oring, or etc that is specific to bank 1. What Does Code P0171 Mean? OBD II fault code P0171 is a generic code that is defined as P0171 – “System Too Lean Bank 1”, and is set when the PCM (Powertrain Control Module) receives input data from the #1 oxygen sensor or air/fuel ratio sensor on bank 1 indicating that the air/fuel mixture has been too lean for an extended period of time- usually about 20. Anytime afr goes above 14. The internal cylinder condition is just as important, […]. This will cause the O2 sensor to signal lean and the ecu to add more fuel which will in fact make you rich. There are lots of faults that can cause rich and lean conditions, but not so erratically. If the correction to the base value exceeds +25% or -25% for longer than 10 seconds a DTC is set for rich or lean stop for STFT. It could be as easy as a small vacuum hose broken. I took the exhaust off of it to clean some things and noticed it doesn’t have an exhaust gasket. Backfiring through the exhaust is a result of problems arising out of rich fuel mixture and out-of-turn sparking of spark plugs. Excessive oxygen readings in the exhaust will set lean codes. The idle mixture screws will only effect the running at idle. I've cleaned the MAF s. Also, some vehicles models are equipped with an air injection system. Try putting your gloved hand over the exhaust as Jack mentions earlier and see what happens. P013A-O2 SENSOR 1/2 SLOW RESPONSE - RICH TO LEAN. Look for an exhaust leak around the exhaust manifold, if nothing try replacing the upstream o2 sensor. Oxygen sensors wear out and need to be changed per your auto manufacturers time and mileage limits. Found no vaccum leaks, not intake leaks, propane test around intake did nothing to idle. I hope you resolve it with the quick fixes. If you are leaking exhaust through a crack, that wouldn't introduce new air into the system. I see many people with their cars and bikes fiddle with these screws, and wonder why it does not help. Although most of the time you need a mechanic's tool set and know-how to fix the problem, there are a few initial. The faulty sensor can cause a too rich or too lean condition. Common causes of backfires are: Wankel rotary engines are known for leaking oil into the exhaust system which causes backfire. Also look for. As the high pressure exhaust stream passes the leak zone, low pressure air (outside air) is drawn in. GM likes to keep us confused. Exhaust Leaks. Other things that can cause it are exhaust leaks - not really a lean condition, just a false reading - whoops saw you fixed that Check for air leaks in any intake piping between the MAF and TB. Possible causes of a rich mixture. Your mechanic can check for vacuum leaks and test the mass airflow sensor with a scan tool. Gray or Blue Smoke from Diesel Exhaust. But after 2-4 starts and. Try looking into that first, and if all of that seems to be fine, then you need to richen the mixture. Basically this means that an oxygen sensor in bank 1 detected a lean condition (too much oxygen in the exhaust). avoid running exhaust fans (bathroom, kitchen) if you have an un-flued or open-flued gas heater, as this may cause carbon monoxide to leak back into the room; this possibility should be tested when you have your heater serviced. Leaks, no matter where the leak itself is located, will lead to a lean condition (if not recognized) and eventually to exhaust side scoring. avoid running exhaust fans (bathroom, kitchen) if you have an un-flued or open-flued gas heater, as this may cause carbon monoxide to leak back into the room; this possibility should be tested when you have your heater serviced. If the oxygen in the exhaust gas decreases, the. Deceptive Oxygen Sensor Codes. Normally the piston temperature is higher on the exhaust side so catastrophic problems will appear there first. However, after checking for vacuum leaks & reading a few forums, I came to the conclusion that they come lean from the factory. A crankcase air leak is a problem many pro saw engines have at some point in their life. * Vacuum or crankcase leaks can cause a lean condition and/or possibly a high idle. However this occurs only on cylinders with bridged exhaust ports. To determine if the lean condition is the result of a vacuum leak, bring the engine up to about 2,000 RPM. and how does a leak in the exhaust manifold cause a backfire. Could a leak between the exhaust flange & cylinder cause a lean condition & make the engine rev faster then normal? Search " " across the entire site Search " " in this forum Search " " in this discussion. But you said those are the only two things that can cause a tailpipe backfire. The low pressure portion of the exhaust pulse will draw outside air in. The addition of unmetered air between the combustion chambers & the oxygen sensor(s) creates a false reading, indicating a LEAN condition. Oxygen sensors wear out and need to be changed per your auto manufacturers time and mileage limits. As a result, The faulty sensor can cause a too rich or too lean condition. Vacuum or Crankcase leaks can cause a lean condition or a possibly a high idle. P0171 CHEVROLET - Fuel Trim System Lean Bank 1Possible causes; Intake air leaks; Faulty front heated oxygen sensor; Ignition misfiring; Faulty fuel injectors; Exhaust gas leaks; Incorrect fuel pressure; Lack of fuel; Faulty Mass Air Flow (MAF) sensor; Incorrect Positive Crankcase Ventilation (PCV) hose connectionIf the P0171 is combined with the P0174 code, it's very likely that the. Then the oxygen content in the exhaust drops (because it is being used up in the combustion process), and the voltage increases (rich condition) and the process repeats, for as long as the car is running, hundreds of times a minute. If left unattended long enough, valves burn out due to the leak, which causes rough running engine. Engine starts, then races for a few seconds and then dies. A too-lean condition may also cause overheating, and prolonged operation will cause engine failure - at minimum, burned valves with the added possibility of burning holes in pistons. Exhaust leak somewhere between the down pipe and the cylinder heads. Lean burn refers to the use of lean mixtures in an internal combustion engine. It's not really that but close enough in description. The third and final common cause for this P0171 lean code on this Corolla with a 4 cylinder 1ZZ-FE 1. A broken or damaged distributor cap allows moisture to leak in that causes a spark from one cylinder to fire out another cylinder. While, Too lean and the converter is unable to convert the hydrocarbons into safe elements; and may not pass a state inspection. Yes, after-firing is through the exhaust, the vast majority of the time is cause by a lean condition. I agree with robert. If you suspect a leaking. I have replaced the: Water pump, 3 row radiator, 195* thermostat, 6 blade fan, fan shroud, checked timing, The car has a partly blown exhaust manifold gasket at the center 2 ports #3&4. – Dirty air filter. Many suspected carburetion issues are actually caused by faults within the ignition system, making this the first place to look before making any carburetor adjustments. Misfire: Anything that causes a misfire or excess hydrocarbon (HC) in the exhaust will result in catalytic converter overheating. The idle mixture screws will only effect the running at idle. Then I will be using water to locate the specific area of the vacuum leak. If the system is injecting air when it shouldn't or has stopped working, it may cause unburned or partially burned fuel in the exhaust gases to backfire. Damage caused to the motor by a leaking exhaust can result in the motor having low compression, but fixing the exhaust at this point won't do a thing to raise the compression. The computer then (falsely)richens the fuel in an attempt to get the afr back in. This causes a big vacuum leak that permits extra "false air" to enter that cylinder resulting in a very lean condition. In that case, your OBDII scanner should be reading a lean 0. a vacuum leak would cause a rough idle that would decrease as engine speed increases. Either way, a lean condition is an indicator of imbalance. The lean condition can be caused by a vacuum leak, which introduces more air into the air-fuel mixture, or by a weak fuel system, which does not input enough fuel into the air-fuel mixture. Probably a good idea to fix the leak anyway Allan (New Zealand). This is a result of working equipment, and is unlikely to cause damage. Be sure to check pressure at all driving modes. Leaks in the brake booster provide a vacuum leak to the engine. “Ultimately, a simple air leak can cause a lean condition that will cause an excess of temperature in the exhaust system, which can cause a thermal event, rendering the DPF inoperable and. The oxygen sensor is in the exhaust stream somewhere downstream of the leak. Discovered small exhaust leak post-cat around the area of the back seat. RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds. That being said, it also depends on how bad an EGR is leaking as to whether the O2 reports a lean or rich condition An EGR that has a small leak (one that would only cause a small shutter at idle for example) could cause the O2 to show rich; because of the inert exhaust gas is displacing the oxygen entering the combustion chamber. A leak at the exhaust flange is worse. Check the engine compression. If you suspect a leaking. Jack up your car while it's running and listen and search for any exhaust leaks before the rear O2 sensor. I've cleaned the MAF s. If the carburetor is supplying too lean of an air/fuel mixture, the engine will run sluggish, overheat or the lean mixture could cause engine damage. Yes, an exhaust leak can cause what appears to be a lean condition. components, leaking injectors, defective O2 sensors, exhaust leaks/pinholes before the O2 sensor, coolant temp sensor problems, and base engine issues such as low compression and incorrect camshaft timing. Vacuum leaks generally cause hesitation or inconsistent component operation (ie, idle valve). An exhaust leak, a loose air boot, or carb can be your problem. I wouldn't replace the fuel injectors unless a scope test or injector balance turns up something. To remedy. Automotive Training, Testing, and Diagnostics. Vacuum leaks generally cause hesitation or inconsistent component operation (ie, idle valve). Leaks in the brake booster provide a vacuum leak to the engine. extra oxygen vs stale air = lean burn. Eastern Catalytic manufactures catalytic converters, manifold converters and converter components for aftermarket and OEMs. Intake manifold air leaks will suck in air, not expel it. An intermittent may be caused by any of the following conditions: A poor connection. Probably a good idea to fix the leak anyway Allan (New Zealand). 0 Mustang Tech: 2: Sep 3, 2007: Exhaust Leak Cause Rich or Lean Condition: 1994 - 1995 Specific Tech: 7: Dec 20, 2006: Back. An exhaust leak can lead to your O2 sensors giving a faulty reading and may cause the code to trigger. It alerts your system when the condition is too lean, or there’s too much oxygen in the exhaust. Such a swing in A/F ratio is a sign that an upstream or control sensor is faulty. When diagnosing rich or lean trouble codes, we always start by reviewing the fuel trims. Due to the unique layout of the boxer engine, the exhaust pipes coming off the manifold are exposed to excessive temperatures. I know I have a slight exhaust leak in the crossover to pass side header on my car due to a poor fit. This is especially true for direct injection vehicles with the lean air/fuel ratios. Appearance & Symptoms: Dry fouling (top) appears as sooty, black build-up. Then the oxygen content in the exhaust drops (because it is being used up in the combustion process), and the voltage increases (rich condition) and the process repeats, for as long as the car is running, hundreds of times a minute. That being said, it also depends on how bad an EGR is leaking as to whether the O2 reports a lean or rich condition An EGR that has a small leak (one that would only cause a small shutter at idle for example) could cause the O2 to show rich; because of the inert exhaust gas is displacing the oxygen entering the combustion chamber. have plenty of ventilation – ventilation is very important as it allows fresh air to come in and fumes to go out. when its not leaned out or misfiring or is it doing one of them To gain more insight as to how an exhaust-leak can cause a temporary lean condition INSIDE THE EXHAUST! (and not inside the engine), try. exhaust leak before or near the ho2s is mounted. dtc p013a/p013c indicating a lack of switch are typically the result of either an exhaust leak, exhaust modification, or catalyst monitor sensor (cms) failure which will cause cms voltage readings to be out of range. Intake manifold air leaks will suck in air, not expel it. If the pipe was so severely restricted to cause misfiring it'd affect the whole bank. This prevents the cat from working properly. MAIN QUESTION: Does an air leak in the exhaust valve area cause a lean running condition? lean enough to do the below Ok, I used the title as I seem to have all of those problems and have a question or two. If the lean condition is gone then replace the MAF sensor. No leak found… I cannot find any leaks in the exhaust system, particularly not between manifold and O2 sensor. Could a leak between the exhaust flange & cylinder cause a lean condition & make the engine rev faster then normal? Search " " across the entire site Search " " in this forum Search " " in this discussion. You can also listen for leaks, which can sometimes be heard making a hissing noise. I have had plenty of drama with this kx100 eating top ends and discussed it here previousl. Other possible causes of blue exhaust smoke include: piston wear, worn valve seals, a dirty or non-functioning PCV valve, worn piston rings, an intake manifold gasket leak, worn engine oil seals and possibly even head gasket failure. They all lead to lean conditions in the mixture. Something like a leaking injector oring, leaking air distribution manifold oring, or etc that is specific to bank 1. Several things can cause this !!! The system will become lean if a fuel injector is not supplying enough fuel. What will be noticeable is the increased fuel consumption. Trying to tune my procharged Trans am and something I am seeing when the car warms up (190-210) is that my STFT's on the drivers side is around 50 and passenger is high too (to be honest I can't remember) before I post a log/scan I was wanting to get some ideas on what may be causing this? From my understanding its a lean condition somewhere (possible vaccumm leak) and the ECU dumbs fuel to. Also, a leak condition can result in air that is not properly measured entering into the engine. More serious turbocharger damage or problems with intercoolers are not. This can cause a hesitation, stumble and/or rough idle problem as well. possible causes leaking egr gasket or leaking egr valve diaphram. i have a 1999 4runner 3. Sorry if I wasn't clear. If you are pressurizing the exhaust system, that would still push out exhaust. Other things that can cause it are exhaust leaks - not really a lean condition, just a false reading - whoops saw you fixed that Check for air leaks in any intake piping between the MAF and TB. exhaust side. Code 45 indicates exhaust O2 rich. Re: Clogged cats causing lean condition? #572043 11/17/05 09:15 AM. Exhaust leaks: If there is an exhaust leak, the engine may pull the outside air into the exhaust. To remedy. An exhaust leak can lead to your O2 sensors giving a faulty reading and may cause the code to trigger. Preforming a plug chop is a good way to find out if your engine is running too lean, as you will see a powdery white residue on your spark plug in the presence of a lean condition. An EGR valve that is stuck open can result in an air-fuel mixture that is too lean. This will also require a scan tool. Exhaust manifold leaks can be dangerous as well as cause other costly problems. Oxygen Sensor– The P0171 codes is thrown when the oxygen sensor(s) do not register enough oxygen in the exhaust. If you have an exhaust leak behind the rear O2 sensor, it should not cause the code. The car almost dies sometimes. Our Universal, Direct-fit, CARB, High Performance and Diesel converter lines cover over 100,000 applications, including OBDII coverage for all 50 states and are certified in 58 countries around the world. working on a 6 cylinder 1964 mustang with AC. Best Answer: YES. I can smell a very faint exhaust smell if I'm leaning over the engine with the hood up,. The P0171 or P0174 misfire code is set usually caused by lean mixture, it can means the engine is getting too much air, or engine is not getting enough fuel, possibly through a leaky EGR valve or a vacuum leak. This can cause rough running, but may not be the cause of yours. 8 liter engine is the front oxygen sensor or air fuel ratio sensor. You can also listen for leaks, which can sometimes be heard making a hissing noise. Exhaust leaks -- If there is an exhaust leak, the engine may pull the outside air into the exhaust and past the sensor. You would just end up passing less exhaust past the o2. A leak after the turbo will make you lean under vacuum and rich under boost. Blue/Gray Exhaust: Blue/gray exhaust is an indication of oil burning in the combustion chamber. Leaks, no matter where the leak itself is located, will lead to a lean condition (if not recognized) and eventually to exhaust side scoring. Vacuum leaks: Have only done a quick vacuum leak test as I have trouble understanding why a vacuum leak would cause a rich condition and if anything a slightly low idle (750rpm) on a MAP engine. just swapping a slip-on pipe for another one wont/shouldnt cause a lean condition. Jump to Latest Follow 1 - 5 of 5 Posts an exhaust leak upstream of the O2 sensors I believe makes the sensors think there's a lean condition so it causes the engine to run richer- this would mean worse fuel economy and worse emissions. Causes of Excessive Exhaust Emissions: As a general rule, excessive HC, CO, and NOx levels are most often caused by the following conditions: Excessive HC results from ignition misfire or misfire due to excessively lean or rich air/fuel mixtures ; Excessive CO results from rich air/fuel mixtures. If you had one, you should have picked it up with your test. ) The symptoms: On a cold start, it always dies at least once. In addition to venting toxic gases forward of the cabin where they might enter the ventilation system, exhaust leaks also affect the way the engine runs. Together with the unburned fuel in the exhaust system and an open exhaust, the sparking results in the. if you find either, pull the rocker shaft off and run a leakdown test if possible. Have a qualified technician check it out. It's not really that but close enough in description. Outside air is drawn INTO the leaking area during the low pressure event. This causes the actual air flow to be higher than the mass air flow sensor measures. then i came upon a very old article taking about the myth of burnt Valves and exhaust leaks. A third sign your exhaust may be leaking is if your gas pedal vibrates while you are driving. A lean fuel mixture would not cause a sulfur smell. This website might help a little with diagnosing what might cause a lean or rich condition and yes, the O2 sensor itself could have simply failed. As the high pressure exhaust stream passes the leak zone, low pressure air (outside air) is drawn in. from what i know, an exhaust leak causes a loss of backpressure. At idle, intake manifold vacuum is high and each cylinder receives a rarified air\fuel charge. This condition is primarily caused by dirty air filters, but it could also result from the incorrect fitting of after-market accessories such as exhaust systems, air filter systems, or replacement carburetors of a different type or size. If the lean codes keep coming back, the MAF sensor may have to be replaced if the engine does not have a vacuum leak or fuel delivery problem. it was talking about modern cars where an exhaust leak can not cause a burnt valve due to the computer compensating for the lean condition caused by an incorrect oxygen sensor reading in the exhaust on a modern car which in turn riches the intake. Step 5: Check for Vacuum Leaks. An exhaust leak, a loose air boot, or carb can be your problem. A catalyst can not clean up NOx unless the level of oxygen in the exhaust is very low. See all 7 photos With the engine not running, to help find any exhaust leaks. Wont be able tk get it on a dyno for a month or so due to shops availability. At its worst, long-term driving with a vacuum leak, elevated temperatures generated by running a lean air-fuel ratio could result in engine damage. You can also listen for leaks, which can sometimes be heard making a hissing noise. Here is a good example of a 1987 Honda Shadow VT700C that is running lean. The sonic wave back to the engine will pull air into the chamber when it is trying to hold in the new charge. The P0171 is one of the more common trouble codes. * If the above are OK, it is a faulty heated oxygen sensor. In many instances this code sets if there is a problem with the fuel system, a vacuum leak, an exhaust leak, or other problem with the engine resulting in it running leaner than normal exists. To keep the engine running properly, the powertrain control module (PCM) tries to compensate for the lean condition by injecting more fuel to the mixture in. Initially I thought it may be due to vacuum leaks , which are really common on older motorcycles. A leak announces its presence with a hissing sound. An exhaust leak near the upstream sensor can cause the downstream sensor to read a steady lean condition. If the lean codes keep coming back, the MAF sensor may have to be replaced if the engine does not have a vacuum leak or fuel delivery problem. 8n exhaust manifold leaking oil discussion in the I assumed it was all carb related, but started the post thinking that a bad manifold leak might cause a power loss as well. Internal cooling system leaks can destroy a catalytic converter. EGR valve tube/gasket leak; EVR solenoid vacuum leak; Secondary Air Injection. Fuel arrives at the engine as a hydrocarbon; if it leaves as unburned fuel, it’s still a hydrocarbon. This could result in fuel trim problems and a check engine light, possibly with Fuel System Rich DTCs, such as P0172 or P0175. my question is about this code p0171. If reused it can cause an air leak that will cause a lean condition in the exhaust and thus the back firing. Jack up your car while it’s running and listen and search for any exhaust leaks before the rear O2 sensor. This causes a lean misfire, where the combustion process ends too soon, sending unburned gas into the exhaust. Normally the piston temperature is higher on the exhaust side so catastrophic problems will appear there first. Exhaust manifold leaks have the effect of “fooling” the oxygen sensor. How does a boost leak cause rich condition? (0. If a main vacuum hose such as the power brake booster feed line has broken or failing off it will cause a lean backfire due to the additional air allowed into the engine intake manifold. Sometimes a small leak will make a ticking noise depending on where it's at. Back-firing is through the carbs and can be timing related, cam related or rich mix related, among other things. 7 TBI C/K Car Forums. Since it's only happening on the rear cylinder I'd check the manifold intake gasket for that cylinder and also make sure there's no air leak around the injector itself. Yet another prevalent cause of Ford P0171 and P0174 ean codes is definitely an engine vacuum leak. The upstream HO 2. 5 volts (lean signal) and over. It is hinting 225* on a 90* day, idling with the AC on. I had tried unplugging the MAF and that didn't help. Catalytic converters can only function efficiently if the engine is operating properly and the exhaust system is leak-free. An intake leak would certainly give you lean condition symptoms. Check for Any Exhaust Leaks. Jump to Latest Follow check for vacuum and exhaust leaks PCV system malfunctioning / valve stuck open check fuel pressure, weak fuel pump / clogged filter because as the passenger side one wears out it puts all the strain on the driver side one and causes it to wear out faster. Newer, low mileage truck owners can skip this paragraph, but many of us like to have a worn out beater truck laying around, or maybe your teenager bought their first car from a not-so-honest guy. So fatten up that mixture with the next 2 sizes bigger jets, metering rods etc. Our Universal, Direct-fit, CARB, High Performance and Diesel converter lines cover over 100,000 applications, including OBDII coverage for all 50 states and are certified in 58 countries around the world. An intermittent may be caused by any of the following conditions: A poor connection. Readjusted valves checked for vacuum leaks with carb spray around intake. 5 volts (lean signal) and over. Can bad manifold gaskets cause this problem. To eliminate your intake leaks, simply attach this Intake Leak Pressure Tester to your turbo inlet and apply compressed air through the standard tire. Now, I have never heard an exhaust leak sound like detonation (if this isn't detonation, then it could fool almost anyone, I promise!) but I guess it makes sense; (or not enough fuel, or anything like that that could cause detonation) then it would cause a lean condition THROUGHOUT all of the cylinders and thus show up on the wideband as a. You can also listen for leaks, which can sometimes be heard making a hissing noise. If the exhaust leak is in the back of the car, well-past the cats & O2 sensor, would it still cause it to throw the code? I have a 2007 2. The main causes for this problem are too quick warm-up, too lean carb jetting (main jet), or too hot of a spark plug range. A vacuum leak is most likely the cause. In addition, if the fuel level is set too high in the float chamber, a rich mixture will result. Those codes do NOT mean the O2 sensors are bad, it means a lean condition has been detected. Vacuum or Crankcase leaks can cause a lean condition or a possibly a high idle. If there are no intake leaks, the next step is to replace the air filter and clean the air flow meter. Excessive oxygen readings in the exhaust will set lean codes. A lot of the above is good info, but nobody mentioned to you that a leak in your exhaust, either at the head or the muffler clamps could becausing your popping. If the system is injecting air when it shouldn't or has stopped working, it may cause unburned or partially burned fuel in the exhaust gases to backfire. Exhaust leaking before it exits the system will result in a lower back pressure, which in turn may cause the bike to run hot. An intake leak would certainly give you lean condition symptoms. Oh stop whining! If you want to diagnose and fix your own car, you need the right tools. The computer throws a lean code if it is receiving less than. At its worst, long-term driving with a vacuum leak, elevated temperatures generated by running a lean air-fuel ratio could result in engine damage. Any leak forward of the oxygen sensors can cause a false reading and a fault code to be set. The preturbo exhaust leak will likely cause more afterfire between shifts since it will cause erratic rich than lean conditions. I had a lean running condition with it once that turned out to be a leaking EGR valve. Over time, the EGR valve can fail in the open or closed position. Generally speaking, an exhaust pop on deceleration will come from a lean condition, and there are several things that could cause that. (they say it is hard to get to so the labor charge is high). Test the (O2) Oxygen Sensor Response to a Lean. Oxygen sensors wear out and need to be changed per your auto manufacturers time and mileage limits. If it is a cracked exhaust manifold, then yes that may be the problem. Can an exhaust leak pre turbo cause a stutter like affect or something similar? I think its a leak at one of the flanges pre turbo, it seems that once the exhaust heats up and expands at one of these flanges the leak stops and so does the stutter, its only on start up when the exhaust is cold, and there is no boost/vacuum leaks. If undesirable sufficient, a lean fuel affliction may possibly result in lean misfire, a rough idle, hesitation or stumble when accelerating, and/or poor engine effectiveness. – Ben Oct 18 '16 at 20:34. You can also listen for leaks, which can sometimes be heard making a hissing noise. a leak as far as 10in past the sensor can cause the sensor to read the outside reference air. A clogged fuel filter can reduce both fuel delivery and fuel pressure. This will cause a "Lean Misfire" condition in the engine. To keep the engine running properly, the powertrain control module (PCM) tries to compensate for the lean condition by injecting more fuel to the mixture in. Lean burn refers to the use of lean mixtures in an internal combustion engine. I see many people with their cars and bikes fiddle with these screws, and wonder why it does not help. The additional fuel will/can cause the catalytic converters to fail and breakup. A shorter spark line would indicate a weak spark possibly due to a lean fuel condition (dirty injectors or vacuum leaks) or low compression (burned exhaust valve or bad head gasket). This of course, will introduce extra oxygen into the exhaust stream, making it appear leaner than it is. An exhaust system leak that may not be audible but can set this code. 5 NA OB with 105,000 miles and I've put new plugs & wires (also did the head gaskets & timing belt). It is going to cost me about $500. At its worst, long-term driving with a vacuum leak, elevated temperatures generated by running a lean air-fuel ratio could result in engine damage. This can cause rough running, but may not be the cause of yours. 4 with a vacuum leak causing "System Too Lean" trouble codes P0171 and P0174. Check for Any Exhaust Leaks. 0 Mustang Tech: 2: Sep 3, 2007: Exhaust Leak Cause Rich or Lean Condition: 1994 - 1995 Specific Tech: 7: Dec 20, 2006: What causes exhaust drone? Classic Mustang Specific Tech: 34: Jun 20, 2006. A lean fuel mixture would not cause a sulfur smell. there is more fuel and less air. An exhaust leak can cause a check engine light for a lean condition but will not usually cause a MAP sensor code. ) fuel pressure - system will go lean, if pressure is too low. coolant leaking into the exhaust chambers would cause a gray exhaust color. Normally the piston temperature is higher on the exhaust side so catastrophic problems will appear there first. More serious turbocharger damage or problems with intercoolers are not. 3 liter with just over 60,000 miles on it I did for a used car lot. Exhaust leaks: If there is an exhaust leak, the engine may pull the outside air into the exhaust. I planned on a tune-up, MAF cleaner, fuel filter, air filter soon. Damage caused to the motor by a leaking exhaust can result in the motor having low compression, but fixing the exhaust at this point won't do a thing to raise the compression. An engine that is running lean may be hesitating. In addition, if the fuel level is set too high in the float chamber, a rich mixture will result. That being said, it also depends on how bad an EGR is leaking as to whether the O2 reports a lean or rich condition An EGR that has a small leak (one that would only cause a small shutter at idle for example) could cause the O2 to show rich; because of the inert exhaust gas is displacing the oxygen entering the combustion chamber. Do you no if a lean bank code always displays the same. However, a vacuum leak such as rotted or loose vac hoses can also cause issues, but you usually get a check engine and the dreaded high idels response. As far as the popping/backfiring goes, I understand it can be caused by a rich OR a lean condition, among other things. Since it is easier to check the intake system as opposed to the fuel system, it makes sense to smoke the intake through the ABS brake booster hose. Exhaust Leak Cause Lean or Rich? was created by Tutti57 Does a manifold gasket leak cause the same condition as a leak at say a flex pipe? I can't wrap my head around the theory of it, whether it's sucking air in or pushing g exhaust out and how that impacts the sensor reading. On the earlier engine I believe the intake manifold is called the plenum. The P0171 is one of the more common trouble codes. , ECT, IAT or MAP) Fuel delivery component fault (clogged filter, low fuel pressure). Why will a lean condition cause a P2096 Post Catalytic Fuel Trim Bank 1 System Too Lean. To keep the engine running properly, the powertrain control module (PCM) tries to compensate for the lean condition by injecting more fuel to the mixture in. Either condition will result in poor fuel mileage or possible engine damage. If the oxygen in the exhaust gas increases, the air-fuel ratio becomes lean. These bikes are relatively sophisticated and changes to exhaust or intake are a sticky wicket without proper ECU compensations. Low fuel pressure will cause lean conditions at any rpm or load range. This causes an incomplete burn which causes the fumes to explode in the exhaust system along with an audible pop or bang sound.