fuels trims, when and how to read them
Thread Starter
Joined: Mar 2003
Posts: 8,319
Likes: 1
From: North Carolina
fuels trims, when and how to read them ok first off, i was told the fuel trims should be near 0%. however from individuals i have heard running a little positive % will give better results. i know they have to be read at part throttle, and i was told to do this after 30 min of driving. i noticed the longer i drove the lower the numbers got. is this why they tell u to drive 30 min? becasue the numbers will get lower? i was comming home from work and my car was running for about 10 min or so. at 2000 rpm constant throttle in 4th it read around 2-3% but when i went into a higher gear it read about 4-6% the other day they started off around 6 and the more i drove the lower it got. went from about 6 to about a constant 2-3% does it sound like im alright? and does the computer compensate itself over time to bring these numbers closer to zero anyway? any imput would be great guys, thanks
Thread Starter
Joined: Mar 2003
Posts: 8,319
Likes: 1
From: North Carolina
Re: fuels trims, when and how to read them also, when i had put the predator in my car at first my fuel trims were near 6% and it felt a lot better over stock, i had a new tune to bring them down to like -3 -2 % and the car felt slow as crap. im not running lean or any knock at WOT and the cars throttle response is awesome now with higher #'s after MAF ends as opposed to before, i didnt change the tune after i did the ends just beacuse it felts so good
Re: fuels trims, when and how to read them It shouldn't make any difference what they are, as long as they don't max out either direction. This is not a measure of burning rich or lean, but a measure of what the PCM is doing to maintain a 14.7:1 AFM. The difference you felt may have been weather or maybe the the PCM learned some; it tunes it's self a lot after being flashed.
Launching!
Joined: Feb 2003
Posts: 243
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From: Fresno,CA
Re: fuels trims, when and how to read them I am sure that this has been asked before, but what other things does it effect when the l-trims are maxed out. I am running into that probablem. And i dont think i have an intake leak. It takes bringing down the IFR table to almost a stock injector to compensate for the l-trims with 50lb. injectors. This was before the holley intake also.
Teching In
Joined: Aug 2002
Posts: 23
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From: Elon, NC
Re: fuels trims, when and how to read them 
But isn't that what burning rich or lean is? The PCM senses that you are burning rich (-ltft / -stft) and compensates by pulling fuel and vice versa? It's like a guided missile's navigation system in a lot of respects. The missile is off to the left, it compensates by changing course to the right, it's too high and it looses some altitude. - LTrims = rich and + = lean, no? So, we can use the LTrims as a reference point to the state of fuel burn... Otherwise, I'm seriously
It shouldn't make any difference what they are, as long as they don't max out either direction. This is not a measure of burning rich or lean, but a measure of what the PCM is doing to maintain a 14.7:1 AFM. The difference you felt may have been weather or maybe the the PCM learned some; it tunes it's self a lot after being flashed.
Re: fuels trims, when and how to read them
I am sure that this has been asked before, but what other things does it effect when the l-trims are maxed out. I am running into that probablem. And i dont think i have an intake leak. It takes bringing down the IFR table to almost a stock injector to compensate for the l-trims with 50lb. injectors. This was before the holley intake also.
Pull the intake and blue the intake to head connection for proper contact and sealing.
