Originally Posted By: artbuc
Originally Posted By: Trav
Originally Posted By: artbuc
I am see something weird on my scanner. My Bank 1 AF sensor is shot with both sensor and heater circuits open. STFT stays flat at zero independent of RPM. Bank 2 AF sensor is responding as expected but something very odd is happening with Bank 2 fuel trims. LTFT stays at +10.9% at idle. It will drop as engine is revved up but always goes back to +10.9% at idle. Bank 2 STFT at idle hovers around -10 apparently trying to offset LTFT. As engine revs up, Bank 2 STFT gets less negative as LTFT gets less positive appearing like it is still trying to compensate.
Two questions. Is it possible to diagnosis Bank 2 without a functioning Bank 1 AF sensor? What would prevent my Bank 2 LTFT from moving to zero when the STFT is trying so hard to get it there? Thanks.
Its possible the bank one sensor you replaced just died (it does happen even with Deso or NGK), replace it and see how the fuel trims respond.
Bank 2 quite possibly has a exhaust leak between the A/F monitor and rear O2, this will really scramble the ECM's eggs and cause the symptoms you describe.
If it is a leak it will be a very small one, check any flanges/gaskets and hanger mounting brackets for cracked welds.
You may need to get the car on ramps and actually feel around the weld when the engine is cold started to feel it because you may not hear it. pull down on the pipe and see if a crack opens.
Installed a new Denso Bank 1 AF sensor. New sensor is working great but it did not change the high LTFT at idle. Still wants to settle at -10.2%. Rev her up and LT trim goes positive as the engine demands more fuel but goes right back to -10.2 at idle. STFT stays +/- around zero as does both LT and ST trims on Bank 2.
In addition to the possible exhaust leak, I wonder if I have one or more Bank 1 injectors delivering too much fuel or perhaps just an erroneous signal from the ECM?
IMO the fact that the STFT varies around 0 is a clear indication of the ECU being in closed loop mode and in control while ensuring the LTFT gets maintained - the fact that the LTFT is not closer to 0, is simply an indication of the ECU realizing that the engine operating conditions dictate a different fuelling map ....................... now the cause for that particular need on that particular bank needs to be found to maybe (!) move the LTFT back closer to 0.
The fact that the LTFT changes with throttle variations, is imo no indication of "Rev her up and LT trim goes positive as the engine demands more fuel" - the change in LTFT is simply an indication of the ECU dictating a fuelling map other than the factory std lab optimized fuelling map that would have the engine always running at LTFT=0 if every parameter on the engine and vehicle is exactly as designed for in the manufacturers lab
Could be a leaky injector, misfiring cylinder on that bank or any one of a host/combination of other things ..........
Would be interesting to see the effect on both LTFT and STFT after a cold/hot/cold/hot drive cycle
Originally Posted By: Trav
Originally Posted By: artbuc
I am see something weird on my scanner. My Bank 1 AF sensor is shot with both sensor and heater circuits open. STFT stays flat at zero independent of RPM. Bank 2 AF sensor is responding as expected but something very odd is happening with Bank 2 fuel trims. LTFT stays at +10.9% at idle. It will drop as engine is revved up but always goes back to +10.9% at idle. Bank 2 STFT at idle hovers around -10 apparently trying to offset LTFT. As engine revs up, Bank 2 STFT gets less negative as LTFT gets less positive appearing like it is still trying to compensate.
Two questions. Is it possible to diagnosis Bank 2 without a functioning Bank 1 AF sensor? What would prevent my Bank 2 LTFT from moving to zero when the STFT is trying so hard to get it there? Thanks.
Its possible the bank one sensor you replaced just died (it does happen even with Deso or NGK), replace it and see how the fuel trims respond.
Bank 2 quite possibly has a exhaust leak between the A/F monitor and rear O2, this will really scramble the ECM's eggs and cause the symptoms you describe.
If it is a leak it will be a very small one, check any flanges/gaskets and hanger mounting brackets for cracked welds.
You may need to get the car on ramps and actually feel around the weld when the engine is cold started to feel it because you may not hear it. pull down on the pipe and see if a crack opens.
Installed a new Denso Bank 1 AF sensor. New sensor is working great but it did not change the high LTFT at idle. Still wants to settle at -10.2%. Rev her up and LT trim goes positive as the engine demands more fuel but goes right back to -10.2 at idle. STFT stays +/- around zero as does both LT and ST trims on Bank 2.
In addition to the possible exhaust leak, I wonder if I have one or more Bank 1 injectors delivering too much fuel or perhaps just an erroneous signal from the ECM?
IMO the fact that the STFT varies around 0 is a clear indication of the ECU being in closed loop mode and in control while ensuring the LTFT gets maintained - the fact that the LTFT is not closer to 0, is simply an indication of the ECU realizing that the engine operating conditions dictate a different fuelling map ....................... now the cause for that particular need on that particular bank needs to be found to maybe (!) move the LTFT back closer to 0.
The fact that the LTFT changes with throttle variations, is imo no indication of "Rev her up and LT trim goes positive as the engine demands more fuel" - the change in LTFT is simply an indication of the ECU dictating a fuelling map other than the factory std lab optimized fuelling map that would have the engine always running at LTFT=0 if every parameter on the engine and vehicle is exactly as designed for in the manufacturers lab
Could be a leaky injector, misfiring cylinder on that bank or any one of a host/combination of other things ..........
Would be interesting to see the effect on both LTFT and STFT after a cold/hot/cold/hot drive cycle