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Thread: Years Later Cos Fuel Quits?

  1. #1
    Join Date
    Oct 2011

    Default Years Later Cos Fuel Quits?

    Hey guys,
    My truck has had roughly the same tune in it for years and years, a COS with extra fuel in boost and semi open loop. Lately I noticed it was down on power and the WBO2 didnt move much at idle. Scanned it, no semi open loop, only open loop, and when it hits boost it deliver a richer mixture.

    What could change? O2s are reading what seems to be normal data, nothing was changed in the software for years. Only thing is the battery disconnected, did the COS get wiped out?

    I'm just getting started with this one but I'm not even really sure what would change so maybe some of you older guys may have seen something? Thank you!

    Could it be fuel filter? Would that deliver proper fuel at idle but restrict boost fuel?

  2. #2
    Lifetime Member Doc's Avatar
    Join Date
    Oct 2005


    Are you saying the truck is still commanding the richer value you put in the file but, you are now lean? Fuel filter, #1 on my list.

    2000 Silverado Full Size 4x4: Forged 6.2, H/C F1R Procharger
    98A4 Z28: 02 PCM H/C Forged 347, 9" Moser 3.73
    V1 V2 99+up RR COS #5 OLSD Dual Stg N20

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