So I have been chasing trans issues in a GP for a while suspecting there was more to this. It seems there might be. I finally took the time to properly go over this car.... In the dead silence of night so I can hear and not deal with traffic. Car is has a slight stumble at idle and carries over to slow throttle positions. I suspect whatever is causing this is also causing some sporadic power issues that are causing trans surging and a P1811 code. I got the trans into default full pressure mode with barely over 5% throttle, just putting around.
Anyway, when reviewing sensor data, the throttles all seem to be steady, idle MAF was .6lb/m, nothing really jumped out except the long term fuel trims were around -14%, and my bank one O2 was trying to stay around .7V but very commonly dropped out to .02V or lower. Bank 2 was very consistent around .78-.8V
I am not sure if these just have a pre and post cat O2 sensor? I am not yet sure how this thing could get THIS far off and not code for an O2 sensor? So I am making the assumption this is the post cat sensor? Never really seen one do this. .8V, then .02, then back to .8....
Figure the fuel trims are a product of the O2 issue but maybe not. Do these have injector issues? Could my injectors be causing the O2 problems? -14% seems a lot and something has to be wrong here.
UPDATE: As I work well into the early AM on this, I determined the LTFT will run -8 to -14% at lower throttles and the more throttle you give, the less negative correction there is. There are times I see the LTFT at -12% and STFT at -10% when rolling out of the throttle.
I decided to unplug the MAF for testing since it is highly suspect. I was surprised that the car did not miss a lick firing up and running but automatically put the car in the default max trans pressure mode! hard shifting instantly. Other than that, i really saw little change in fuel trims and the same supected O2 sensor was rolling down to .02V. This the the sensor in my software that is attached to the STFT so I assume the precat O2? Actually both O2 sensors will roll back to lean but bank one is the one that really shows it the most and very consistent.
So.......... What the heck is going on here??? Almost like the ECM is screwed. It is pulling back fuel all while the O2 sensor is reading lean.... No wonder the car runs good up top. Trims realign and at the same time, the O2 sensors start hovering around .6-.7V. I honestly think the O2 sensor works fine but for some odd reason, the ECM is pulling back fuel.
Starting to scratch more on fuel pressure and injectors.... This "miss" is REALLY faint! Like I am have been wrenching a long time and totally missed it. You really need to be listening to hear it and certainly hard to feel in the car most of the time.
Originally Posted by BillBoost37
