dren70

Newbie question here. What does the pcm do at WOT specific to a/f ratio?? I think it uses a preset table and pulses the injectors at a fixed length without regard to O2, MAF, MAP, etc.... Am I correct on this one or am I out to lunch? And if I am all hosed up please straighten me out. Thanks.

David

ulakovic22

I'm no expert, but I believe you are correct. I think it is called the PE table and under WOT your computer points to this table instead of using the normal sensors used in closed loop operation.

Injuneer

The PCM reads the mass air flow from the MAF sensor, calculates a target A/F ratio from the Power Enrichment (PE) mode tables, divides the mass air flow by the target A/F ratio to get the mass fuel flow requirement, then calculates the injector pulse width required to provide that mass flow rate of fuel. The injector pulse width is not "fixed length".... it is variable based on the described calculation.

There is no correction made to the pulse width calculation based on the O2 sensor feedback. However, if the learned long term fuel corrections (BLM's) were "adding" fuel in closed loop, the PCM will use the Cell 15 long term corrections to calculate the pulse widths. If the PCM was cutting fuel in closed loop, the BLM's will default to 128 (= a multiplier of "1").

PE target A/F ratio is a function of MAP and coolant temperature.

In essence, there's not a lot of difference between "closed loop" operation and "power enrichment" mode operation, other than the fact that in PE mode, the target A/F ratio is richened, and there is no "learning" on the long term fuel corrections, and no use of short term fuel corrections.