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adjusting fuel trims

This is a discussion on adjusting fuel trims within the Computer & Tuning forums, part of the LSx Technical Help Section category; when adjusting fuel trims with a predator for example will adjust for partial throttle and WOT at the same time ...

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    Senior Member Wheeler99WS6's Avatar
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    adjusting fuel trims

    when adjusting fuel trims with a predator for example will adjust for partial throttle and WOT at the same time or are they in two seperate areas?
    1999 T/A WS6 Black -------SOLD
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    Don't know anything about the predator, but I assume it would have to be 2 separate areas since part throttle is closed loop and WOT is open loop.

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    The fuel trims are only effected at part throotle,,, whatever fuel trims you have at part throotle, get used while in PE mode (WOT) if they are positive. Negative fuel trims do not effect PE mode, the fuel trim, if negative, is used as zero in PE mode, as to not lean the motor out and cause detonation.

    Typically in tuning a car, we attempt to get the fuel trims between 0% and -5%. In that way, there is no added fuel at PE comimg from the fuel trims. For the proper PE mode AFR, the added fuel all comes from the PE fuel tables.

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    Senior Member Wheeler99WS6's Avatar
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    So basically what you are saying is, I can not lean it out but I can keep it from getting richer?

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    Quote Originally Posted by Wheeler99WS6 View Post
    So basically what you are saying is, I can not lean it out but I can keep it from getting richer?
    As far as how the part-throttle tune affects the WOT tune, that is correct. If your part-throttle ltrim numbers are negative, they go to zero when you go WOT, thus not changing the fuel level. If your ltrim numbers are positive, they will keep that positive value even when you go WOT, thus adding fuel in addition to whatever your PE tables do to WOT fuel.

    As I understand it, having positive ltrims in itself is not really a bad thing, but it complicates your WOT tuning effort. With negative ltrims, you don't have to worry about them at all when tuning for WOT.

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    Senior Member Wheeler99WS6's Avatar
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    I am still a little confused, I am not very knowledgeable when it comes to tuning. I am a little rich at WOT (according to my AFR) and would like to at least get it into the stoich so I could pull a little more power out of the car. How does one accomplish this?

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    Stoich is 14.7 and thats for part throotle and idle stuff. For WOT, you want to run around 12.8:1,, I have been running around 13.0 to 13.1:1 which is called (I think) "lean max torque". You do not want to run at stoich whan at WOT, you will for sure detonate the motor.

    What is your AFR while at WOT?

    If you are richer than 12.6 or 12.8,,, and you have Lterms that are positive (LTFT & STFT fuel trims will always keep you close to 14.7 while cruising), you can lean out WOT by adjusting the LTFTs to be around -5%. You can accomplish this very easily with the MAF translator, which is an old time tuning device that I used back in 2000 and 2001. If you have a full PCM tuner (like LS1Edit or HPTuners), than a small adjustment to the MAF table will fix you right up. And there are other ways to lean out WOT, but these two are most effective.

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    I actually do not have a wideband, just a cheap Air to fuel ratio gauge, it does not tell you the actual numbers. it has a lean section, stoich section and a rich section. at WOT i am on the 2nd of 6 bars into the rich section (i think there is six bars in each section. During partial throttle it is always right in the middle of the stoich section.......Also I was asking how I would go about leaning out my WOT with a handheld. i.e. Predator or VHP handheld. I know they say you can adjust your fuel but not sure how in depth they go. I didnt know if they would let you only adjust for partial throttle or just WOT or what. I plan on getting a dyno tune after the install of a cam and stall possibly even throw in some heads but was hoping to get a handheld to get a little more out of the mods I currently have because I am not sure how long it will be before I get cam and stall.

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    If you're going by your cheap AFR gauge only, you may already be real close to where you want to be. Like Doc99SS said, WOT AFR should be around 12.8 give or take, which is richer than the Stoich number. That may show up on your gauge where you said it was reading.

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    Damn,....Wish I would of knew about the wideband before I got the AFR. If I did I would know where I am right about now.

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    Wheeler, so how far from Monroe Michigan are you? I have a wide band O2 meter and LS1Edit.

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    Not sure I am located in Terre Haute, IN. I am willing to bet it is pretty far.

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    Monroe Michigan is 20 miles north of Toledo, laying on I75. You are always welcome to come over, but its a major trip for you. Right now I am in the midths of replacing my blownup LS1 engine with an undecided stroker short block.

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    If it wasnt so far I would for sure. I appreciate the offer.

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    Not a problem, its about 350 to 400 miles for you.

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    I have a Predator and they are both separate!! Easy to tune/modify when monitoring in real time mode!

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