Josh

iTrader: (9)

It seems that every tuning document I've read mentions that one of the functions of the VE table is to provide a comparative value for the reported MAF reading. I've not been able to find, though, an explanation of what happens when the VE table thinks the MAF is wrong. Particularly, which of the two values is used to determine fueling?

I realize this shouldn't be an issue if the car is tuned properly, but just for the sake of discussion, I would be interested to know.

Thanks,
Josh

soundengineer

iTrader: (16)

IF VE is correct and MAF is wong...it mucks up the tune for any part that uses the MAF
IF the MAF is correct and teh ve is wrong..then it mucks up the tune where the VE is wrong...

basically when any part is wrong..it mucks up the tune

txhorns281

iTrader: (12)

i also believe if the disparity b/w the two airflow calculations meets a particular threshold, the PCM will immediately fall back on SD operation (as that is supposed to be the more conservative, secondary system by original intention and setup). This disagreement would usually happen when the MAF electronics fail in some way, causing the two calculations to conflict greatly with each other and would be followed by a MAF DTC. If the MAF and VE were tuned so distantly in error, I'm not sure if the PCM sets a condition for a warning of some sort, but I rather doubt it would need to since the car would most likely be running like total crap and you definitely would notice. The range in which is acceptable b/w the two calculations is probably pretty lenient (at least lenient enough to allow +- 15-20% disparity as we can see that trims are allowed to swing b/w +25 and -25), so the difference b/w the two would have to be waaaaaaaaaay off either intentionally, or by idiocy... I've never cared to wander that far to find out

soundengineer

iTrader: (16)

it takes about +/- 25 in LTFT before it gets to that point of thowing a code from being out of whack...
or there are also a few tables that compare to various MAP values vs MAF amounts that can get too far as well and throw a code....(this is usually teh problem vette guys run into when they ask about reduced power mode)

Josh

iTrader: (9)

Good info, thanks, guys.

Josh

redtail2426

iTrader: (10)

i noticed the other day on my car that my lower ve values(10-20% throttle/under 2000 rpm)were way to low and what would happen is the car would run smooth and then all of the sudden jerk and hesitate a bit.The jerking was from the computer jumping down to that lower ve value which in turn puts you at a much lower spark advance on the spark tables.Bottom line,the car wont run as smooth as it should.