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Thread: cold start lean issue

  1. #1
    Tuner in Training
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    Oct 2013
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    ft collins colorado
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    cold start lean issue

    So here's the issue: engine first fires up and is rich enough to run ok for about 3 seconds then the engine goes very lean even though eq ratio is about 8.9 to 1 afr. I have no plans to leave it that rich, I did lean it out and it's worse. I haven't put my wide band in it yet, just going off of the o2's. This is a speed density tune I just started on. After it runs for about 3 to 5 minutes it runs good and smooth for a big cam that Idles at 65-70kpa. Any thoughts would be appreciated.

  2. #2
    Tuning Addict 5FDP's Avatar
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    May 2012
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    Rogers, MN
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    8,164
    Without a wideband you are just guessing based on the o2 sensors. It could be richer or leaner than what is being told by the sensors and the commanded AFR/EQ ratio.

    It may say 9 AFR commanded but it could really be 8.0 or 12.0 because of how far off the fueling might be. It's not worth it to chase this issue if nothing has been done to correct it yet. Get it running and start getting your data logs so you can really see how far off it is and correct it.

    Try removing some of the negative timing that your ETC spark correct table is using. It's pulling up to 8 degrees.

    Also make sure you have no vacuum leaks or exhaust leaks too. And double check you are running 58psi of fuel pressure.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

  3. #3
    Tuner in Training
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    Oct 2013
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    ft collins colorado
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    thanks 5FDP for the guidance, finally got my wideband in it and now i'm seeing the issues. I've been doing this for twenty years and sometimes you get off track and do stupid stuff. there is a method to our madness!!! literally! Thanks again.
    Wade