02NBMZ

I swear + is rich - is lean. Like right now, I am at +25% ltrims and my A/F ratio is a pig rich at 9-10%. This would lead me to belive I am running a tad bit rich. Am I right or did I completely miss something ?

Vettepartz

This is the way I try to remember it. You are looking at an air to fuel (A/F) ratio. NOT fuel to air. The computer wants something like 14.7 parts air to 1 part fuel. If the RATIO is +25%, then the air part is more (maybe 25%???) so overall you are running lean because you have too much air. The numbers may not be exact here, but I think the principle applies.

Scalpel

iTrader: (4)

+ = lean
- = rich

Glenn98ZM6

+25% ltrims is not rich or lean. thats not what that value means. the car is adding 25% (maynot be accuale value) more fuel that stock. at 25% it stopps adding fuel (+25% is max for the computer). the computer is trying to compensate for a lean condition by adding fuel. @ 25% Ltrims you RUN THE RISK of being lean due to a lack of enrichment from the computer.

where are you getting the 9-10% rich value from. do you have O2 readings?

<small>[ May 08, 2002, 06:05 PM: Message edited by: Glenn98ZM6 ]</small>

MY99TAWS6

iTrader: (3)

Yep you are lean so computer is adding 25% more fuel to compensate..so after it adds it you may not be lean.You should be setting ses lights right around there as was also said that is borderline to the range the computer can compensate for.What the heck can make your car that lean..headers make it richer and my new cam seemed to slightly lean things out..but just slightly.And my ls6 intake didn't do much either.
Your injectors must be way too small or you are shooting a huge dry shot or what..??

JAS

Glen98ZM6 - <img border="0" alt="[chug]" title="" src="graemlins/gr_chug.gif" /> <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

Ltrims are just a correction factor between the air flow the MAF is reading and the what the O2's expect to see to achieve a desired A/F. It's called a closed loop system. That's why when you port a MAF your ltrims sky rocket. The MAF is telling the PCM that it see x-amount of air when it actuality the engine is injesting a ton of unmetered air. So the PCM expects to only fire the injectors for that small bit of reported air. Then the O2's react and go what the hell, there is a ton of air here and not enough fuel command by the PCM to reach our goal of 14.7 a/f. So the PCM CORRECT's for this condition by adding fuel ON TOP of the base COMMANDED fueling which is commanding less injector flow because of the MAF.

Think of it as a closed loop balancing system. It's a PCM algorithm to correct for such things as vacuum leaks aft MAF as well MANY other changes (header leaks, etc.. etc.. etc..)

The point is, at part throttle, you are NEITHER rich or lean based on ltrims. Now at WOT, you will need a WIDEBAND to be able to tell.

Now your job is simple. Correct what is wrong so the system can work within it's parameters. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

Glenn98ZM6

just so i can get the hang of making MAF calibration changes, can i use my idle RPM range and adjust the MAF to bring down the Ltrims @ idle. and once i feel comfortable with that, start making my part throdle changes, and then the WOT changes? of course i will need to know what fuel cell i'm in @ idle, P/T, and WOT - right? this will be after i find out why my idle Ltrims are maxed of course.

also - i understood how the Ltrim thing worked, just not what the #'s directly represented. so Ltrim = the amount of fuel the motor needs (ultamately determined by the O2's) over what the MAF tells the computer the motor needs. right?

Ragtop 99

iTrader: (7)

I would not start messing with segments of the MAF table until you log your LTRIMs and see what is going on accross the whole range. Chances are you are off everywhere and could use constant factor to make your first adjustment.

smokin' joe 00 ss

I have the same problem at idle I will see 25% on my Ltrims and at crusing speed 2100-2500 rpm's I'll see -1.6 on my ltrims and at WOT I'll see .935 on the 02's and I have my maft set all the way rich on the base and 0 on the WOT and this is with the stock maf with the gmaf I couldn't get my Ltrims below 11.5% at crusing speed. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

parish8

iTrader: (6)

newbe question here, if your ltrims are not pushing the + or - 25% do you need to worry about them? if they are at lets say +15% doesn't that mean the computer is doing it's job and adjusting it to run right or will it actualy run better if your ltrims are closer to 0?