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Thread: Random large negative fuel trims questions

  1. #1
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    Random large negative fuel trims questions

    i have a 99' T/A with 243 heads and a 231/234 torquer v4 cam along with supporting mods, ive taken a couple data logs of the car and ive been informed before that the tune is a MAF only tune and that it should have had the VE table dialed in. the car seems to run fine other than a crappy idle once it goes into closed loop as well as a hanging idle at certain times and smelling like raw fuel at idle im guessing from a false lean condition from the overlap of the cam. 'checked for vacuum leaks already and replaced every sensor on the car' when i do scan logs and look at the STFT some logs they're in between + and - 10% and some logs i do they drop all the way down to -40% im just wondering if the tune is really that far off or if i possibly have a bad ecu or some other problem, only reason i would suspect a bad ecu is previous owner burnt one of o2 wires on header which i put new wire in, but unsure if that would short ecu and cause problems.

    thanks in advance.
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  2. #2
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    What sort of injectors are those?

  3. #3
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    they are 42lb fuel injector connection, i know that the injector data is wrong compared to the excel spreadsheet flash drive that came with the injectors. from what i can tell is the guy set it up as 50lb injectors but i could be wrong.

  4. #4
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    That's why you're having problems. Can you post the excel sheet?

  5. #5
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    this is the plug and play spread sheet i got with the injectors

  6. #6
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    Way different. Retune with correct data. Check the transient fueling tab, too.

  7. #7
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    With a injector of that size you will need to reduce or zero tables ECM 2284 and also ECM 2282.
    This is critical.


    Some people say reduce it.. I've never had a issue zeroing it out.

    That cam is on the edge of what will work well with a MAF sensor and for a GEN 3 its on edge for letting fuel trims control fueling down low. You should use a wideband to tune this car.
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  8. #8
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    That's what I did in that tune. Set Min Pulse to repeatability based on SPA. Matched 2284 to that. Zeroed 2282. Set cam timing. Entered other data as presented in the excel file.

    ...and I just realized I uploaded his excel file instead of that tune. Here it is.
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    Last edited by SiriusC1024; 05-21-2024 at 06:45 PM.