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Thread: Cammed C7 idles but has negative timing. 3 bar map sensor seems to be reading high

  1. #1
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    Cammed C7 idles but has negative timing. 3 bar map sensor seems to be reading high

    So we have a cammed and supercharged LT1 C7. First start up sounded great but now the car seems to be pulling timing at idle and it sounds terrible. We put a 3 bar map sensor in it and we pulled the info from an LT4 tune. The car starts and sounds great but as it warms up the timing starts to go negative. The map sensors seems to be reading real high. Does this look right?
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  2. #2
    Senior Tuner Ben Charles's Avatar
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    Lt4 sensor is closer to 4 bar if that’s the one you are using..

    Need to dial in fuel on VVE and MAF and most likely timing will fix itself.. about half the time depending on cam size I have to mod VT

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    I was told the LS9 and LT4 sensor are the same. Was that bogus info from my dealer? I'm pretty sure it's a ls9 map sensor. Should I switch to 312.50 and Off-Set: -11.25

    I wanted to fix this idle before I started on any of the other tuning.

  4. #4
    Senior Tuner SultanHassanMasTuning's Avatar
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    key on engine off log

    also whats your cams specs
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    GPI stage 2 cam. I'll get the log in a bit

  6. #6
    Senior Tuner Ben Charles's Avatar
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    Quote Originally Posted by JASON11WS6 View Post
    I was told the LS9 and LT4 sensor are the same. Was that bogus info from my dealer? I'm pretty sure it's a ls9 map sensor. Should I switch to 312.50 and Off-Set: -11.25

    I wanted to fix this idle before I started on any of the other tuning.
    Ls9 snd lt4 are not the same

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    Custom Mid Engine chassis, AKA GalBen C

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    I went over the the LS9 specs but it's still pulling timing and trying to pull the idle down. I also took the negative timing out from the minimum spark table but it still oscillates. In gear as soon as you hit the gas the car will accelerate on its own. It's like it's in cruise control. Never had this happen like this. I brought the idle down (cams not to big) to maybe 700 and lowered the torque external load. Same results.

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    here's the koeo scan. map seems okay now.
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  9. #9
    Senior Tuner SultanHassanMasTuning's Avatar
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    dont remove the minimum timing, you will through off all the torque calculations
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    Yeah, so much for the tuning school. I feel like the entire coarse on Gen V was misleading info.

  11. #11
    Senior Tuner mbray01's Avatar
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    As stated, properly tune both maf and vve, and timing will correct itself. The map reads high, because the torque is off, and its opening the throttle body to compensate, and then the ecm pulls timing to correct the high idle condition. Its a snowball effect.
    Michael Bray
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    Thanks. I was worried something else was causing the high map readings. Any advice on how to VVE tune a gen V car? Everytime I disable the maf it goes into limp mode

  13. #13
    Senior Tuner SultanHassanMasTuning's Avatar
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    cam spec and whats about fuel lope

    also mentioned which supercharger
    Last edited by SultanHassanMasTuning; 05-30-2020 at 03:57 PM.
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    n./Ex. Duration
    223/235
    In./Ex. Valve Lift
    .639/.639
    LSA
    113
    ICL
    +4


    It's a YSI on a A&A kit (low boost)

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    It's not a extreme cam. Just got a code for P0121 throttle/pedal position sensor and P2230 Barometric Pressure Sensor A Intermittent/Erratic

  16. #16
    Senior Tuner SultanHassanMasTuning's Avatar
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    ok did fuel lope on that cam stock?, did you do a breakout harness for the MAF?
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    It's a 32% overdrive fuel lobe. I did not run a breakout

  18. #18
    Senior Tuner SultanHassanMasTuning's Avatar
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    check PM
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  19. #19
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    Have you tried clicking "Throttle Cleaned" under Engine > Airflow. My truck was acting dumb, and not closing the throttle enough for idle, I tried everything, VVE, MAF, VTT.. and just clicking that got me back to 12-15 deg idle timing, and the throttle blade would close like it should.
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  20. #20
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    I disagree. Tuning the VVE and MAF to 0% doesn't always fix this negative timing. That being said fuel is way off in this log. Definitely get that in order first. What tb is on the car?
    Last edited by sevinn; 05-31-2020 at 03:45 PM.