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Like to Look at PI Corrections as a Diagnostic Tool? Consider This.

2K views 3 replies 4 participants last post by  Michael Plummer 
#1 ·
A little tip for people, who, like me, liked to use PI Corrections to verify no vacuum leaks and things still running well.

PI Corrections are no longer the instant diagnostic tool that they once were with the older UTune strategies, which did not have adaptive controls. This isn’t a bad thing, but it does require a little change in thinking. Here’s a simple example.

In the past, let’s say they you got everything set up properly. You dialed in idle speed and injector low slope, and as a result your fuel PI Corrections were near zero at idle. If down the road you happened to notice that PI Corrections were suddenly 10% at idle, that was almost a sure sign that a leak had developed somewhere. It didn’t need extra fuel before, but now it does. Why? Likely candidate… unmetered air is getting in somewhere that it wasn’t before. (I discovered a vacuum cap had cracked on me by doing just this before. Even bigger example was my friend's car whose supercharger inlet with a draw through MAF had become partially uncoupled from the blower.)

With Insight and Adaptive Learning, those corrections are going to shift to the adaptive tables. At the moment the vacuum leak develops, the PI Corrections will go up. However, if the condition isn’t caught immediately and stays relatively the same, the ecu will “learn” that it always needs to add that 10% extra fuel at idle to compensate. The 10% additional fuel will shift from the closed loop (essentially short term) “PI Corrections” to the long term adaptive learning table. Once those tables are written, the engine basically runs off what it has learned and real time correcting no longer needs to take place. PI Corrections ultimately go back to 0. If all you do is look at PI Corrections, it won’t be immediately obvious that something has gone amiss.

What you can do is look at your adaptive table. If you did the setup properly with adaptive turned off and cleared, and you got your PI Corrections down near 0 before turning the adaptive back on, then you shouldn’t see large corrections added to adaptive table in the low load areas where the engine idles. (In my case, that’s around load of 0.2.) If after time passes you see that 10% corrections are in the idle area of the adaptive table, that could be a sign that something has changed.
 
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