02sierraz71_5.3

iTrader: (2)

Ive been doing lots of reading for days now and at first I thought the world was on its head and gas laws just didnt work anymore but, now it makes sense.
When temps go up gases still expand and density still decreases.

The problem is the IAT increasing and everything going leaner is actually thanks to GM and incorrect cylinder charge temperature modeling and how the ECT and IAT are filtered together. The pcm is overcorrecting for increased temps, there are also other prevalent design errors like location of IAT.

http://www.hptuners.com/forum/showthread.php?t=6345
I wish I could take credit for this discovery but I cant WS6firebird and soundengineer resolved the problem each with thier own unique ways I think its very interesting to see how people reverse engineer GM's mistakes and come up with thier own completely different solutions. A VE modifier table would be nice based off ECT and IAT!
This is why I still run a MAF.

Below is a letter from chris at HPT to soundengineer. Throwing it out there so others dont have to scan through 100's of posts.

"The equation is very simple:

airmass = VE.MAP/MAT

airmass = grams/cyl
VE = grams.Kelvin/kPa
MAP = kPa
MAT = Kelvin

MAT is the estimated manifold temperature, which in earlier OS's is simply the IAT, but in later OS's uses the blending of IAT and ECT dependant on airflow. The issue seems to be worse in the earlier OS's due to this fact. If you don;t see the "Use Complex Model" setting then its just using the IAT, even though there may be a bias table shown it's not used.

With intake/cam etc. changes it's not unreasonable for the MAT estimation to be inacurrate, and it's not unreasonable to assume the factory calibration is inaccurate as well

So you can see from the above equation, the PCM assumes that the air density is a linear function of pressure and temperature, which the gas laws dictate. In my opinion most, if not all, of the SD error seen as IAT changes is due to the MAT estimation being wrong, non-existant or due to heatsoak on the IAT sensor itself. This seems to be backed up by the fact that people say trims go positive at hotter temps because the PCM thinks the air in the manifold is hotter than it actually is due to heatsoak/inaccurate calibration of bias tables.

This is why most decent blower setups ensure the IAT sensor protrudes enough into the airstream and isn't measuring aluminum temperature at low airflows.

Hope that helps,

Chris..."

cylinder charge temp bias vs airflow: should be set to 1 so it takes into account ect and iat evenly.

Thanks to those who did all the work

Yelo

Good Info !!!

bigredexpress99

iTrader: (15)

by george, I think I've got it!!!

Okie5.3

iTrader: (1)

that was a good read. glad there are folks like them to "nuke" this stuff out.

02sierraz71_5.3

iTrader: (2)

As an added note this will throw the VE table off by around 20% so be prepared to retune

MikeGyver

iTrader: (5)

With my IATs always being more or less 10° over ambient, S/C, with air-to-air intercooler, and complex model disabled, is the reason that my truck runs so much better when it is in the 70s out compared to when it is in the 80s due to what this post is about, or just because it does? (Was that sentence long enough?)

Yelo

Dude...that was the hardest sentence I've EVER had to read

I believe you're on the right track with your thinking....

MikeGyver

iTrader: (5)

Does my truck run so much better with a 10 degree drop because:
1. The computer is misinterpreting what it should do according to IATs, or,
2. Just because it is supposed to run so much better at 76 degrees than it does at 86 degrees?

02sierraz71_5.3

iTrader: (2)

YES, if you have an '02 and later pcm the complex modeling will be enabled from the factory. With it disabled the modeling goes solely off of IAT vs complex that integrates IAT and ECT this is better because the IAT seems to become heatsoaked very easily in the stock location and doesnt allways represent what the intake charge temp actually is nor does it respond fast enough to changes in temp.

Are you using the maf?
Do you have a 2bar map?
where is the iat located exactly?

MikeGyver

iTrader: (5)

I am using the MAF, relocated to between the I/C and the engine.
No 2bar.
IAT has been relocated to the top of the intake manifold, right before the air enters the runner. No heatsoak, temps are always about 10° over ambient, might go 20° over after long WOT runs, and drop back down in seconds to +10°.
Oh yeah, it does heatsoak with the engine off, of course.