Fuel tuning on Supercharged W-Bodies. MAF vs VE relationship

[dlagrua]

A friend of mine has done a code disassembly of the 03 Grand Prix PCM for a 3800SC series III engine. He has evidence to suggest that the VE table (on the w-body PCM) is used only as a backup for fueling in case of MAF failure. He maintains that under normal operation, the fueling control is derived mainly from the MAF output signal and PE tables while the VE tables on these PCM's are not used unless a backup reference is needed in the case of MAF failure. My tests seem to indicate that this is so. Can anyone confirm this?

[MMGT1]

Many, many discussions about this over the years. Your PCM will reference it through transitions, and also while in OL. A VE tune in the idle region is necessary for some builds, ie: big cam... etc. Do the VE tune, it's worth it if the MAF fails and will help the idle region quite a bit. As I said, Ive seen quite a few guys test this out over the years, and I will always do a VE tune now just to keep things tight and proper. On my v-6, a 3400, the VE table is not supposed to be referenced unless MAF failure, of so I was told. Had an issue of a lean spike between cruise and PE mode. I finally gave in and did just a rough VE tune on it and poof~ spike gone.
I have also seen v-6's just as you say there, adjusting VE to the tune of even zeroing it out had no effect on the scan or trims at all. In the end, some do, some don't. imo, tune it anyway, it's there for a reason

[dlagrua]

I guess the argument of the relationship of the VE table to overall fueling will go on and may be vehicle dependent. I am of the opinion that on some GM PCM's the table is used as a reference table for the MAF during normal engine operation and on others like the w-body cars, it may be there to be used only as a backup in the case of catastropic MAF failure. I believe that Bill from HP would know for sure (as he owns a 3800SC).

[murphinator]

if you have ever had a maf fail on a L67 without a tuned ve that has some basic mods like 3.5 , intake , headers you will always do a ve tune afterward - happened to me 2 states from home - they dont want to run very well

[dlagrua]

if you have ever had a maf fail on a L67 without a tuned ve that has some basic mods like 3.5 , intake , headers you will always do a ve tune afterward - happened to me 2 states from home - they dont want to run very well

Must agree that the VE table needs some tuning on modified engines BUT we must also recognize that the VE table serves no purpose other than to provide back up fueling values in case of MAF failure. During idle and cruise conditions the MAF signal/tables is the primary input for fueling with some help from the fuel modifiers and PE table at WOT. I don't know about other vehicles but on the L67/L32 PCM's this is the case.

[darkhorizon]

if you have ever had a maf fail on a L67 without a tuned ve that has some basic mods like 3.5 , intake , headers you will always do a ve tune afterward - happened to me 2 states from home - they dont want to run very well

I have never had stock VE give me many problems other than a funny idle at times.

[smallblock500]

had a MAF go bad on a L67 once on the highway the car would not go over 20 MPH so i got out and unplugged the MAF and the car a lot better it was left like that until we could get a new MAF for it. After that the VE table was tuned just in case it happened again.

[jimmyblue]

I just looked at my first V6 tune file yesterday, and the VE
table was all 0.80 - which makes it pretty much garbage.
Is this the norm, stock '99 Bonneville?

[GeoJB]

I just looked at my first V6 tune file yesterday, and the VE
table was all 0.80 - which makes it pretty much garbage.
Is this the norm, stock '99 Bonneville?

NO!

Pull a tune from the repository to get a comparison.

3.8 or 3.1?

[jimmyblue]

It's a 3.8 NA car that's just had a supercharged 3.8 swapped
in (and now gets dismal MPG and performance). I've pulled a
few repository tunes to draw from. The OS in this car was one
HPTuners didn't support, so they made me a new beta version
that will at least open it. But I see a very sparse set of params
when I do, much less than I'm used to seeing on a V8. I don't
know enough yet to say if it's normal and crappy, or somehow
wrong.