There must be some hidden code buried deep within the PCM. It seems no matter how close I adjust my trims they will eventually go positive! I've tried with and without the MAF and the trims do whatever they feel like.

I'm wondering if this has to do with long tubes and the fact that my sensors are so far down stream. Very frustrating!

 

Have you disabled COT

 

If you mean Cat Over Temp, yes.

 

Ive noticed the same thing. Sadly nobody has any in depth info on it, but it may help explain your LTFT drifts while the MAF is plugged in. Looks like dynamic airflow (VE) has its own trims or offeset. During steady state it calibrated dynamic airflow to match up with the MAF's reading. It does this so the engine can for all intents and purposes make adjustments to the VE table as the engine wears or as it becomes modded. I think this may be causing our grief.



Steady State
A critical part of the dynamic airmass calculation is determination of when the engine is operating at a steady state condition or unsteady (transient) state. During steady state the PCM uses a filtered MAF signal as the basis for airmass calculations, the PCM also calculates a "VE Correction Factor" during steady state. The VE correction factor is simply the ratio of the MAF airmass to the VE airmass and is used to "offset" the VE calculated airmass when a transient is encountered.

During unsteady state, the PCM uses the VE table to calculate airmass and it is offset (multiplied) by the last calculated VE Correction factor. As long as the VE Correction factor is within limits it will accurately offset any differences between MAF and VE table airmasses and the transition between steady and unsteady (transient) prediction will be smooth.

 

Perhaps that's the key. Where is VE correction factor stored? I assume it's stored for safe-keeping if it feels the table is not right. Then basically the VE table can be anything as long as it's close +/- 25% of what the PCM calculates?

 

Are you sure the o2's are not going south?

 

They're not that old. They have about 20k on them and they seem to read evenly.

 

Its probably not the o2's then. However they do have a shorter life in long tube/heads/cam cars. I've seen some people go through them every 20k.

 

Well, pulses do look a little hagard when cold. They are very sluggish to get going but seem OK when hot. I'll replace them and see what happens.