One day it will be in the 12.5-7 range and then sometimes it will be in the 13.2-3 range,i dont get it..All my ltft are 0 to -4 so it never gets to lean .what else has an effect on WOT fueling.??

 

Exactly why having a negative fuel trim set isnt desireable.

 

air temps and engine temps....
you will need to populate the AFR vs ECT add and AFR vs IAT add tables properly
or redo your cylinder charge temp bias(works on 2001/2002)...
neiter is an exact esay task to do..but can be done

 

i thought a positive fuel trim set was worse as it will add fuel to your wot if its a lean ltft.I rather have it negative then positive.

 

That's what I thought too.

The only table I see that should affect pe fueling is measured vs ect, and even in a stock file it's set to 0 between 140 and 212. No reason for it to be any different.
Where is this IAT vs AFR table that affects pe fueling?

 

Think about this.

What does the computer do at wide open throttle and regular driving when there is a positive trim.

It makes the changes to get the fuel back to where it needs. Including wot.

If it sees that there is a 3% change needed at regular cells, then it also assume that the same needed change would be needed at wot.

What happens at wot say with a neg 8 trim and you tuned your car, now, the needs of the car have changed and it is showing neg 1 trim.. How much has your wide open fuel been off now.?

 

I thought the whole point of getting your ltft's on the negative side of 0 was so that the pcm would see that the ve and maf (or whatever it's using for it's main fuel calculation) is on the rich side at part throttle. Then when it goes to wot there would be no reason for it to add any additional fuel. LTFT's should go to 0 at wot?
If the ltft's are always on the plus side of 0, the pcm knows it's constantly adding fuel at part throttle, so it will also use the ltft to add fuel at wot?

Otherwise, what's the point adjusting the ve table and/or maf table at all? Depending on atmospheric conditions from day to day, fuel trimming will vary...then so will wot fueling? That just doesn't make sense.
If that were the case, wouldn't your trims need to be 0 all the time in order for the pcm to not add fuel due to whatever it learned from the fuel trims?

 

Exactly, When it goes to 0% correction at wot, there is no fuel correction. BUT!!!!!! the fueling needs change all the time. So if you perfectly tuned your car at wot, and say the car is -1 at all driving cells. It is Exactly perfect, BUT now, 3 days later and 20 degrees different temp, you are now -7% and now your WOT is still 0% correction, but you will see that your WOT fueling is 6% different.

Now take that same situation on a car that is tuned on the positive trims... HMM

 

im still not seeing this,my car was tuned for positive bfore it was negative and the wot was way more unstable.Thats whe whole reason all the tuning docs say get the VE as close to zero or slightly negative.Which is what i have.Most of my cells are -1 to -2..99 percent of the time now its dead on but yesterday it was showing slightly lean.I might just recal my wideband and see if it fixes it.

 

... and the worst thing, is that the narrow band O2s are giving you the rich/lean information. I can get my VE table lined up with a wideband to less than +/- 1%, day-to-day stable, and the fuel trims report that some of the VE cells are up to 4% rich. Wait4me has the right idea, though, if the low MAP VE cells need more fuel, doesn't it stand to reason that the WOT cells would too? I'm presently using Soundengineer's charge bias discovery to keep things stable in open loop speed density. It would be nice, though, to have a sane set of compensating values for PE ECT & IAT tables.

 

Is your Desired AFR set at 12.5-7?

Are you leaner on the hotter or cooler day?

 

it seems like its leaner on the hotter day,which still isnt making sense.All i know is that i tuned the ve and MAF to 0 or -2,slightly rich lets just say.And then i tuned the PE table until i got it in the 12.6 to 12.8 range.Now it seems like on the hot days it runs a little leaner.

 

you don't tune the PE table to get your desired airfuel, you set the PE table to your desired airfuel ratio, ie if you want 12.6 you take 14.64/12.6=1.6169 and you set the PE table to this value, then you alter the airflow characteristics to get WOT fueling correct.

Ryan

 

You want to know whether the change is in the commanded
fuel air multiplier, or whether you are commanding the same
AFR and not getting it. There are environmental adders that
will push on fueling.

The fallacy behind adding closed loop last-cell positive trims
to the big-end fueling is that the two have very little in
common - airflow basis (SD vs MAF) for starters and all of
the speed density side low-RPM error elements that have
nothing in particular to do with WOT airflow at 4000+ RPM.
But GM did it and you're stuck with it, so get it clean.

A large negative fuel trim -might- indicate richer than
necessary WOT fueling but I wouldn't put any particular
credence to that; measure it, know your commanded
FAM/AFR and figure out who's off script.

 

Wait4me i understand your explanation and i may experiment with it again.Thanks for the info everyone,i will start scanning.

 

I disabled complex charge temp on my 2002 car. Im just adding a touch of fuel below ~50* and above ~90*.

Shoudl I go back to the complex mode? I notice my VE is skewed quite a bit from one method to the other.

 

say you wanted 13:1

14.64/13 =1.1261

are you saying if someone desired a 13:1 AFR from 3000-6500 rpms they would use the same value (1.1261) in all the PE table cells?

 

Yes, The PE table is a "commanded air fuel ratio table when in PE mode" You want to set this to the value you want to acheive, and then change the airflow values to get the WOT fueling to match the commanded air fuel ratio.

Ryan

 

^^^yup... there are other methods, and they all work, but this (VE Tuning) seems to make most sense to me...

Set PE to what you actually want... if your VE is accurate then the PCM commanded and actual AFRs will be very very close

Others do MAF corrections, Injector corrections, or just PE corrections to get actual AFR to where they want (yet commanded may be much different)


keep in mind though that you may not want 13:1 across the board for max power under the curve.... this is where a dyno can be helpful... since at the track/street it's more difficult to determine what AFR at different RPMs the engine likes the most

 

To add to this thread:

Just tuning my car last night I had trims 0 at WOT the week before. Bolted on a ported TB and my LTFT's when from -3's all around roughly to +2's and +3's... Consquently I also noticed my WOT LTFT's were +2 all across the RPM range. Crap...

Went and redid the MAF cal (thinking this may be the issue) and loaded the new one in. Trims initially were 0! Thought the problem was solved! Of course the trims had simply been reset. Did some WOT runs and saw 12.6:1 right off the bat with a stock PE table in the car (1.25's across the board up top) which is commanding 11.8:1. Crap. What's up? Then added some timing. Did another pull, car worked great with about a 12.7:1... Cool. Leaned it a bit to 1.23 in the PE and went for another pull (3rd gear for all pulls) and figured I'd see 12.9:1 or something... yeah.. WRONG. Car showed 12.3:1 and showed +3 LTFT's at WOT.

While I was tuning the first 3 WOT pulls were all LTFT's of 0 at WOT. The car must have "learned" into a positive state at WOT. That's why my AFR jumped rich on me.

To test this theory, reset my long term trims with the scanner and went out and did another WOT pull immediately. AFR? PERFECT 12.9:1... Hmmm.

So am I right in saying the car is learning into positive WOT trims on me?