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Thread: Negative timing at idle on LT4

  1. #1
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    Negative timing at idle on LT4

    So a customer has a CTSV gen 3 with the LT4. Car is full bolt ons and it was tuned by a big internet tuner (not saying this is there fault by any means). Customer brought the car in with a miss fire on cylinder 5. We changed the plug and checked the wire. Everything looks good but it's still miss firing. On the scanner it looks like it could be because it's pulling timing at idle. -5ish degrees. Could the Nick Williams throttle body be the culprit (its been on the car for about two years)? Could it have gone bad? Is there a way to relearn the throttle body to the ecm with the HP scanner? Any other tricks? I added like 50 rpm to the idle and let in some more air but it didn't seem to change anything.

  2. #2
    Senior Tuner Ben Charles's Avatar
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    Sounds like the ECU is commanding too much air/Tq, so it’s doing all it can to pull spark to correct it hence the negative timing

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    Quote Originally Posted by Ben Charles View Post
    Sounds like the ECU is commanding too much air/Tq, so it’s doing all it can to pull spark to correct it hence the negative timing
    Isn't it the other way around Ben? Delivered is higher than commanded so it pulls timing and lowers idle to correct?
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    Strange thing is the car was unchanged for some time. So to pop up out of no where I just wonder if something mechanical is acting screwy.

  5. #5
    Senior Tuner Ben Charles's Avatar
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    Quote Originally Posted by HeavyChevy305 View Post
    Isn't it the other way around Ben? Delivered is higher than commanded so it pulls timing and lowers idle to correct?
    That is 100% correct!!

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    Quote Originally Posted by JASON11WS6 View Post
    Strange thing is the car was unchanged for some time. So to pop up out of no where I just wonder if something mechanical is acting screwy.
    Did you check for vacuum leaks? I was chasing neg timing at idle and it was from a leaking BOV.. different for you I know, but same concept, more air goes through at idle then it is counting on.
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    Didn't see any issues. Does anyone know how to relearn the tps sensor with the scanner?

  8. #8
    Senior Tuner mbray01's Avatar
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    it just started doing this, or nobody noticed it till now. I see tons of big name tuners, or top tuners who are lazy and dont properly model the airflow. I see shop posting videos talking about how big and bad their build is, and you can clearly hear the thing pulling massive amounts of timing, its so unhappy.

    IF it just started doing this, there is an idle reset(throttle cleaned reset) that you can perform, i find it best to perform it key on engine off, then restart and see how it does.

    if its always dont this but nobody has really noticed what its doing, then it will need a proper tune to correct it
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  9. #9
    Tuner Camaro6's Avatar
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    Is the virtual tq and driver demand tables oem stock or altered calibration? That could be culprit #1. Is the MAF scaled to compliment the NW tb along with the throttle area limits "max area" data number? I see this issue when guys put 95mm tb on the LT4 and then have no timing. Let me know if you need assistance on getting the car dialed in.
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  10. #10
    Senior Tuner eficalibrator's Avatar
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    Back to basics first... Is the VVE properly calibrated (steady state without the MAF to small open loop lambda errors)? If VVE isn't right, the torque model will suffer. The torque model IS idle control on GENV. We have several training videos walking through this available on our site.