My GN has always had an issue with some low BLM values when coasting down in speed. I have played with the MAF tables a lot and fixed it all up except for one cell. Most cells are within 5-6 counts of each other. I have moved BLM cell boundaries around to isolate the problem.

Right now cells 0,1,2,3 are 0-10 g/s of flow. At a dead idle below 1000 RPM I am in cell 0 and its fine at 126-128. The problem is Cell 1 is at 105 and is 1000-1500 RPM. Cell 2 is 1500-2000 RPM and looks not bad at 118-120. Cell 3 is never really used. The other rows are fine.

I was wondering about things like the PCV valve being open or not but that should raise the value not lower it. Is there just a weird flow problem in the exhaust that could cause this?

Its just a pain to have everything normal except for this one problem area.

 

Well if its only deceleration it could be oil.. During deceleration you pull lots of vacuum thus pulling oil past rings and valve seals if bad... Thats if tuning does not seem to cure.
Could also be PCV as mentioned if it is stuck open, if its stuck open you really wont pull much raw air from crankcase unless you have a leaky gasket somewhere.. so there for you would read rich from the oil. Try unplugging (of course cap fitting) and then see.

 

I will try pulling it out and plugging it.

 

Might look at the deccleration enleanment, DFCO stuff.
Is there a drivibility problem?, or just worring about the numbers?.
Depending on how you drive, you might try disabling the DFCO.

The GN has a rather large plenum, so on throttle close there can be a fair amount of wall wetting, and an intial richness is normal, and then as the time in deccleration increase, the walls dry out, and you get to finally go lean.

 

I don't ever seem to be in DFCO while in the problem cell but I cannot say that for sure, I will check. I have tried to drive in that cell but I basically can only just kiss the throttle to stay in it, while in that state I have seen the number drop down by one, later on it came back up.

Driveability is good, its just I don't want to have a cell pegged. The stock lower limit was 100 so I am not far off of that for some reason.

 

Code is a series of compromises. Sometimes some areas are so minor, that not alot of effort goes into them. And you may have hit one. A couple of the others, are the lack of refencing AE to RPM/Load, after all once in any degree of boost, and PE you really don't need, much if any AE. Then there's the lack of populating the IAT/MAT timing correction area.
Not to mention the GN code is very old.

 

Actually, I plan to add timing changes with temperature soon after moving the temp sensor somewhere useful.

I wanted to fix the one weird cell so that as I change chips and reset the ECM I don't have to wait as long to see what my changes are. If its an off-idle thing I am working on I have to make sure that cell is happy and not masking a problem.