I know you guys thought this thread was long gone...

Sorry to open this back up, but..........I've got an interesting question that I've always thought about and could never resolve a solid answer for myself.


Let's take a stock corvette and note the fuel trims after a drive.

After adding a CAI and Headers, the fuel trims rise by about 8% or so clearly reflecting that we've added airflow and the compensation trend is for the pcm to need to add about 8% fuel to bring it back in line.

This seems to hold true for LS1 and E40 pcms using a conventional VE table and a MAF.

Back when the E38 first appeared in Vettes, I noticed that I'd add the same CAI and Headers and would take her for a drive and the fuel trims would be the opposite....The LTFTs I was tracking would go negative indicating that the pcm had subtracted fuel as if it was too rich...

But Why? In the LS1 example we've ADDED AIRFLOW and fuel trims went up indicating the need for more fuel.....

Why is it that in the E38/E67 controllers ADDING airflow caused the trims to dive negative? Doesn't adding airflow dictate adding more fuel?

While I've got plenty of these vehicles under my belt now and I've got it working to my liking....I often wonder if I've missed something simple here....

At times I've assumed that the new generation of MAFs gets overstimulated by an increase in airflow and/or over reacts at low airflow....or maybe that a vortex of air is responsible for the overstimulation?

Maybe it's just because the math and the lack of a conventional VE table has changed?

In principal, they should be the same....and it threw me for a loop for the first bunch I tuned.....But, then it just became the same old "just make em' happy" procedure....

Anyone ever thought about/notice this besides me?

I welcome your thoughts.
Chuck CoW