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Thread: Running very rich on decel

  1. #1
    Join Date
    Dec 2017
    Posts
    11

    Default Running very rich on decel

    Gíday from Australia.
    I have a stock 5.7 aluminium block ls1 with ls6 intake.

    Iíve fitted the MSD atomic ls kit and itís running and performing well.

    I had to get my exhaust emissions tested this week to pass registration and it failed.

    The test sheet shows that the air/ fuel ratio is spot on during the rev range, but the ecu is dumping fuel in each time you take your foot off the accelerator to change gears causing it to run quite rich, particularly when itís closer to idle.

    Are there any adjustments I can make to keep the fuel ratio correct on decel?

    Cheers
    Steve

  2. #2
    Join Date
    Nov 2015
    Posts
    108

    Default

    Are you running stock cam setting? What is your IAC count at idle? You may need to open up your throttle blade alittle.

  3. #3
    Join Date
    Dec 2017
    Posts
    11

    Default

    Thank you.
    Iíve reset it to all the factory defaults again.
    Yes, with stock cam setting.

    The iac count is running around 30 at idle.
    Ive got a/f set at 14.7 for idle and part throttle.
    Itís at 12.8 for WOT.

    Iíve got the timing at the default of 0.

    I noticed thereís an enrichment setting for TPS and MAP, both set at 25% - is this right?

    I might have to take it for another drive after resetting to defaults so the ecu can learn again.

    It runs perfectly, apart from failing the emissions test due to the rich decel only.

  4. #4
    Join Date
    Nov 2015
    Posts
    108

    Default

    TPS and MAP will enrich when it see’s a change in manifold pressure or throttle blade change. I have mine set as low as 8 and 10. Still think I need alittle lower. Every engine is different unfortunately so there is no set point to start at. Try lower the some and see what you get. I run my WOT richer but it also changes under boost.

  5. #5
    Join Date
    Jan 2010
    Location
    Brisbane, Australia
    Posts
    919

    Default

    Hi Steve,
    Factory ECMs cut fuel on decel, where as aftermarket generally don't.
    That is your first setback.
    Gary (Brisbane)
    PM me for discussion.
    Regards

    Gary

  6. #6
    Join Date
    Dec 2017
    Posts
    11

    Default

    56B96B0A-DA68-4CA3-90C6-37DD8B743D80.jpeg
    7C4146D5-C2B5-46F5-9635-85F913395F7D.jpg
    A copy of the test result and requirements to pass the emissions test.

  7. #7
    Join Date
    Dec 2017
    Posts
    11

  8. #8
    Join Date
    Jan 2010
    Location
    Brisbane, Australia
    Posts
    919

    Default

    Interested in what happened at the 90 second point in the graphs.
    Regards

    Gary

  9. #9
    Join Date
    Dec 2017
    Posts
    11

    Default

    I went back for a second test today.

    The fellas let me in to help out with tuning on the second run.

    Turns out the problem is actually no fuel on decel. It leans out to almost 20:1 and then doesn’t burn the fuel resulting in hydrocarbons going through the roof.

    So the issue isn’t rich on decel it’s fuel cut off.!!

    Does anyone know how to turn the decel fuel on?

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