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Thread: Lean hesitation with cold engine TBI

  1. #1
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    Lean hesitation with cold engine TBI

    Guys I need help with a lean hesitation, for a tbi 305. Has 081 tpi heads, lt1 cam and some other mods. Runs good when started cold till the temp gauge gets to about 140 degrees then hesitates. Once warmed up to 200 degrees runs good again. I get a hesitation when accelerating the more throttle the bigger the hesitation. I have the fuel pressure and blms tuned close to ideal. What table should I adjust to get rid of that hesitation. I am using a painless harness and 7747 ecm.

  2. #2
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    Quote Originally Posted by 92TBIVentura View Post
    Guys I need help with a lean hesitation, for a tbi 305. Has 081 tpi heads, lt1 cam and some other mods. Runs good when started cold till the temp gauge gets to about 140 degrees then hesitates. Once warmed up to 200 degrees runs good again. I get a hesitation when accelerating the more throttle the bigger the hesitation. I have the fuel pressure and blms tuned close to ideal. What table should I adjust to get rid of that hesitation. I am using a painless harness and 7747 ecm.
    The TBI head tunes run a good bit leaner than the TPI head tunes through warmup despite being TBI. Might add some fuel to the coolant temp vs MAP table in the temperature range you are experiencing issues in. Also might need more MAP and TPS AE in those coolant temperature ranges. Is it in open or closed loop when this happens?

  3. #3
    EFI GearHead ! EagleMark's Avatar
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    At those temps it's probably not a fuel table and it's Closed loop by then. As Fast mentioned it may be AE TPS and AE MAP.

    One thing that helps and some people still overlook Stoich AFR! With E fuel it's 14.12 and when we had none E fuel it's 14.7... this is all it takes for a lean warm up issue!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  4. #4
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    I have a 3 wire o2 sensor on it, so probably closed loop, unless there are some other factors involved for it to go closed loop. Thanks for the reply

  5. #5
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    I am running gas with 10 percent ethanol that is what is available mostly unless you get premium at some stations. I'll try bumping up those ae map & ae tps values. Should I start with one or do both at the same time? Thank You

  6. #6
    Fuel Injected! steveo's Avatar
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    if you dont have a stoich setting for it to go off of, you can just bump your injector constant or base injector whateverthehell, its pretty much the same, that's what i did with EE.

    drives me nuts trying to get it close here on any vehicle, i have a variation of 0% to 15% ethanol in our local pump gas, which is fine if im near home (i've determined which station is 0% in the premium pump), but if i fill up somewhere else i can feel the difference.

    only real solution is to run it a bit rich and just let 'er trim for cruising economy when its running 0%. it's not like it minds a bit of extra fuel in other situations anyway.

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