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Post engine modification I was getting a P0172 (Fuel trim system Rich) code in both my original PCM as well as my new PCM. Due to my injector size upgrade it was thought that a mini AFC would be able to adjust for such a modification, as the NEW PCM did not have the new injector size programmed in it. It was found that my O2 values (by means of a Tech 2) were fluxuating anywhere's between 50-1100 MV. LTFT values were in the range of -22% at idle, and never dropped above -15% at WOT, and the STFT was around -7% at best. The Mini AFC was found to be of no help at the time, so after much research and questioning I decided to have my PCM flashed with my 'new' injector size, and see if that helped.

Just this week I installed my new PCM, and the difference in the car was night and day. I allowed the newly flashed PCM to learn for 2.5 days before I put the Tech 2 on the car to see if it had rectified my problem. My LTFT is much better now and was between -14 and -12%, and the STFT was right around 0. The computer hasn't flashed any codes so that would indicate that the Fuel Trim values are withing the parameters for the PCM to compensate (11% either rich or lean I believe), however,,,,,,,, my O2 values are still fluxuating between 50-750 MV so I am unable to trim the car to where it should be (940-960MV).

I have further details for those who require them, but for now I just thought i'd leave it at this.

I am wondering if anyone has seen such an occurance with their O2 sensor. Also wondering if I may be able to tune using the AFC and the LTFT/STFT values as opposed to the O2 values.

FYG at present:

-The O2 sensor is new.
-Rear O2 sensor is a simulated value
-MAF @ idle 3000 hz
-MAF @ idle 8.3 g/s
-Injector pulse @ idle 2.3ms
-A/F ratio 14.7:1

Thanks in advance to anyone who might be able to shed some light in order to get the "little darlin'" working where she should be. :)
 
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