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Thread: Boss with popping under decel

  1. #1

    Boss with popping under decel

    Got this twin turbo boss thats popping under decel. Looks like spark is dropping under decel. Verified no exhaust leaks. Decel spark is set at 60. Looks like torque base decel. Anyway to tune this out?
    Last edited by Stangguy; 12-29-2016 at 06:04 PM.

  2. #2
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    The popping is normal, happens on stock cars with stock exhausts too, it's just the cats and stock system does a okay job at cancelling the sound. When you go with a aftermarket exhaust you will hear it more.

    I think there is a DFCO option you can turn off, I don't have my comp in front of me right now to double check though. The thing is engine braking will be affected when it is off, you will notice revs come down much slower...MPG will be affected slightly too since the injectors aren't cutting off during decel.
    Last edited by Jn2; 10-07-2016 at 09:33 PM.

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    Okay I opened by file to take a look at the DFCO in the tune

    Engine>Fuel>Cutoff/DFCO

    What you can do disable DFCO is mess with the enable and disable RPMs.My tune has enable at 1,200 RPM and disable at 1,000rpm...There is also a enable/disable speed, play with those to find the right numbers to make DFCO never enable, or make it so it doesnt enable at parking lot speeds(assuming your customer is just concerned about loud popping when driving slow)

    so to disable it in parking lot speeds you could try:

    Enable Speed: 20mph
    Disable Speed 20mph

    to disable it completly you could try the following. I havent tested them, but by the descriptions logic, these settings would set the enable rpm so high DFCO would never kick on and you would get no longer have popping from the exhaust.

    Enable RPM 8,000rpm (or something higher than you will ever go)
    Disable RPM 7800rpm(still higher than you would go)
    Last edited by Jn2; 10-07-2016 at 09:50 PM.

  4. #4
    Wouldn't that cause a rich condition and more popping. The car pops for those couple seconds before DFCO kicks in

  5. #5
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    Quote Originally Posted by Stangguy View Post
    Wouldn't that cause a rich condition and more popping. The car pops for those couple seconds before DFCO kicks in
    no it would not cause a rich condition bc the car would continue to maintain a lambda 1 during decel vs cutting off all fuel and retarding timing

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    It would cause more fuel than cutting fuel. lambda 1 is richer than lambda 2. you want the least amount of fuel and the most amount of timing as possible to prevent pops. the opposite for pops.

    You can increase timing at low load in the calculated torque /inverse tables MP 0, and 10 if you have a 11-14. your decel spark source is mainly tipin/out and torque control(torque tables). This would allow you to get to the 60* allowed at all RPMS for low loads. you can try maxing out all "deceleration fuel cutoff" and lower the "dfco enable/ disable cutoff normal" RPM closer to your highest target idle rpm. so 0 mph for enable/ disable, max load 2, n/v 0, ramp on to 50 and off to 100 (to leave room for transitions), delays to 0.

  7. #7
    My low load timing in the mid and higher RPM is 30-50 degrees in my spark tables. I adjusted for the dfco, but where do i adjust the timing for the torque tables as your saying for decel.

  8. #8
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    'i ment borderline and MBT spark tables.

    In the torque management you can raise the fuel cut torque ratio limit towards 1 for tip out. This should cut the fuel sooner. It can cause a lean knock if you rapidly let off and get back on the throttle so watch out for that. Raising the value for spark torque ratio limit for tip out and decel should prevent the spark dips. decel is the blank cell right below engine over temp. Same goes for spark only torque.

  9. #9
    Thanks mufie. Got it nailed down. Need to get some of these tables properly populated in HP. Would of made it a lot easier.