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Thread: LTFT +25, STFT Maybe +5 - Needs More Fuel

  1. #1
    Fuel Injected!
    Join Date
    Nov 2019
    Bossier City, Louisiana

    LTFT +25, STFT Maybe +5 - Needs More Fuel


    A buddy of mine in an A-body Chevelle with a mildly cammed LS1 motor has a maxxed out +25 LTFT and maybe a 4-5 STFT. I think his tune done by somebody else needs some extra fuel to get his LTFT back down to a reasonable level. That "somebody else" won't help him to make adjustments. Its +25 LTFT on both cylinder banks. Stock LS1 intake and exhaust manifolds and he's going to get me the exact specifications on his camshaft. He's running stock LS1 fuel injectors and I have a copy of his current BIN which if I remember correctly is a 12208322 and I have a good XDF for that tune. He also has a spare PCM that we can experiment with and I have plenty of others on my shelf so that we can leave his current PCM untouched. His engine idles well and starts easily and we don't believe he has a vacuum leak anywhere. His engine and transmission does not indicate any DTC codes or a check engine light.

    I'm reasonably adept with Tuner Pro RT for VATS and all of the systems and DTC's that need to be killed off in a tune but I've never touched an OS to increase or decrease fueling. What tables are involved here that we should adjust to make LTFT come down to something less than +10?

    Many thanks,

    1970 Chevy El Camino, LM7 Engine, 4L60E - Two 896 and two 0411 PCM's

  2. #2
    Fuel Injected! ralmo94's Avatar
    Join Date
    Feb 2020
    Assuming the injector settings are correct

    Usually adjustments are made to the airflow tables, namely VE Tables, And MAF tables.
    Most fail the MAF in the tune so it runs strictly off of the VE tables so they can be dialed in.
    Easiest way to do that is to change the value for MAF error high to some thing like 1 or 2 hz, so it sets the error imiatly.
    You want to make sure that that MIL code is set to 1st error.
    If you disable the code, it will still use the MAF table and not enter speed density.
    This should trigger the SES light on the dash if equipped in the swap.
    Once VE is dialed in change the code back to normal and dial in MAF.

    Check out STEVO's trimalyzer for dialing in the VE.
    He wrote it for old BLM systems, but I use it for OBD2. Just change it form 128 is good to zero is good.
    It's really nice to be able to combine data logs
    Last edited by ralmo94; 04-02-2022 at 09:58 PM.
    No need to re-invent the wheel. But we can make it better

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