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Short term and long term fuel trim readings can ANYONE help?

This is a discussion on Short term and long term fuel trim readings can ANYONE help? within the General Help forums, part of the LSx Technical Help Section category; i know i know this isnt the place for this question or opinion on this type of issue but im ...

  1. #1
    poor bastard DaytonaBlues's Avatar
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    Question Short term and long term fuel trim readings can ANYONE help?

    i know i know this isnt the place for this question or opinion on this type of issue but im gonna ask anyways.

    I have a code scanner which allows me to view my short term and long term fuel trims. so far, my short term trims both banks are between 0% and negative 3.5%. UGH... whats worse is my long term fuel trims are over 11%!!!
    im just asking if anyone with this kind of knowledge can tell me what my STFT and LTFT should be with my mostly stock 99 LS1 (Z28). its a six speed with a Fast toys ram air, lid and a SLP loud mouth.

    i was told my Long term fuel trims should never be above 5% positive or negative. (mine right now are like i said around negative 11% to negative 13% (LEAN?!?!)

    any links or the like to point me in the right direction to help me understand what they SHOULD be would be greatly appreciated...
    thanks for any help!
    99 z28 m6 ss clone
    79 Z28 (fast as Fu*k) thanks rich
    SLP Loudmouth, Founder's LCA's, BMR APHRD, Tranzilla T56, Exedy clutch SLP Lid FTRA Powerslot rotors 'brock strut brace, SS wheels and SS hood, hurst, 1LE bars, Energy bushs, EBC's
    past: 95 T/A, 78 Z28, 98 Z28, 86 Z28, 00 GSXR 600

  2. #2
    Veteran 0rion's Avatar
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    Negative trims mean you're rich not lean. Another thing to factor in are what cells you're in when looking at your trims. You are rich.....mods & has it ever been tuned? Keep in mind that ltft's are just averages of your short term trims so get your short term in line across the fuel trim cells & your long term trims will follow. Just sounds to me like you need a tune.

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    pajeff02's Avatar
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    ^^ This. Trims should ideally hover around zero, meaning the PCM is not adding or subtracting fuel.

    How old are the O2 senders? Has your car been tuned? MAF been cleaned lately? Air filter in good shape?

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    poor bastard DaytonaBlues's Avatar
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    all my 02 sensors are new Bosch 13444 i got from Rockauto. all 4 of them are new..well except the one behind the cat on bank 1, which is not the original 02 sensor but still it has been replaced, but the two upstream sensors are new. I do have a SES light on, says 0443. which my scan tool told me was low catalyst performance threshold bank 2. air filter is in good shape, its a K and N, but god knows the last time it has been cleaned...

    the PROBLEM is perhaps my MAF because it has been descreened by the previous owner. But i did go ahead and clean the maf with that CRC mass air flow cleaner spray and worked great.

    and to adress what orion said..yes the car has some minor engine mods, bolt ons, such as an SLP lid, k and N, descreened maf, what looks like a Fast Toys ram air, and an SLP loud mouth (the loud original one)

    the car MIGHT have had a Predator hand held programmer used on it but i have no idea how to tell if a tune was done...the previous owner said he was going to include the tuner with the car so i got no clue about how to tell if he actually used the tuner.

    so basically my LTFT's are not worth paying attention to, its my Short term trims that matter right?. they are ALWAYS negative. usually they swing from -0% to -3.5%. sooo i guess the thing is running really rich. side not is that i sealed my airbox from the SS hood which is functional, so the only air coming in to the motor is from under the car, and the filter is a little dirty, but it is after all a K and N. the descreened MAF worries me but other than a pretty loud valvetrain knocking from the drivers side rocker cover (i think) the motor runs great. but again, the fuel trims are nuts. if it helps at IDLE my timing sits at around 30 degrees, and goes up to over 41. my coolant temp as well NEVER gets over 195 then the fans kick on. on the highway cruising in 6th the car sits at right at 170 degrees.....wowsers..so there must be a tune and a low temp t stat.

  5. #5
    Experienced Old Fart jfl330's Avatar
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    Your car is running about how GM wanted it to. A little rich so it doesn't knock and have you break an internal part. If it were my car, I get rid of the K&N and it's oil that coats your MAF and put in a paper filter every so often, cheap and flow about as good. A tune can get the trims closer, but im my opinion, certainly not worth it. Don't know how many miles you have, but a fresh set of 41-110's go a long way.

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    Agree. Your trims are not that far off the mark. Heck, I have seen mine maxed at 25 when I accidentally crossed up my harnesses under the car, but we won't tell anyone that story. I agree that you should ditch the K&N and go with either a good paper or nano fiber dry media filter.

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    poor bastard DaytonaBlues's Avatar
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    Question thanks for help

    Quote Originally Posted by jfl330 View Post
    Your car is running about how GM wanted it to. A little rich so it doesn't knock and have you break an internal part. If it were my car, I get rid of the K&N and it's oil that coats your MAF and put in a paper filter every so often, cheap and flow about as good. A tune can get the trims closer, but im my opinion, certainly not worth it. Don't know how many miles you have, but a fresh set of 41-110's go a long way.
    holy chit thanks for the help. the car has only 119K on it. and what the heck are 41-110's??? 0xygen sensors?? i do have brand new Bosch 13444 02 sensors on the car now.

    what decent paper filters are out there besides a pos fram? the k and n thats in there i dont think has ever been oiled or nothing..and well yea the MAF has no screen but i cleaned the wires good with the MAF cleaner. should i swith to a paper filter? like i said i use a sealed airbox..wondering if i open up the actually ram air inlet from the hood (SS hood) it might help lean the car out. maybe the car isnt getting enough airflow through the maf????
    right now the only air that gets to the engine comes from that 4 inch wide by 12 inch long slot that is underneath the air filter. (the super sucker or Fast Toys ram air, i cant tell which one it is)
    Thanks for the help yall

  8. #8
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    41-110's are Iridium AC Delco spark plugs.


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