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Thread: Cool Weather Backfire

  1. #1

    Default Cool Weather Backfire

    The weather has been cooling off and I have noticed a slight backfire at startup when the temps are lower. At idle, it's not noticeable, but under acceleration it becomes more distinct and clears up after a couple of blocks. Any idea what's causing this?

  2. #2
    Join Date
    Dec 2009


    If everything else is fine, the Cranking Fuel (lb/hr) may be a little too lean, or the IAC Parked Position % may be a little too much.
    Since you didn't provide any data (such as AFR), I suggest recording a datalog of this occurrence; it should reveal the problem.
    In order to tune the starting parameters, it's often necessary to turn the ignition key on, wait for the WBO2 sensor to
    display AFR
    , then start the datalogger & engine. This allows you to determine if the engine AFR is excessively rich or lean. (Good Starting Advice Thread - Especially posts #2, #4 & #6.)
    May God's grace bless you in the Lord Jesus Christ.

    '78 BRONCO: 508" stroker, TFS heads, 11:1 comp ratio, Dominator MPFI & DIS, cold air induction, Spal dual 12" fans/aluminum radiator, dual 3" exhaust/Magnaflow mufflers, Moroso vacuum pump, Accusump, engine oil & trans fluid coolers, 100HP progressive dry direct-port NOS, A/C, LenTech Strip Terminator wide-ratio AOD/2500 RPM converter, 3:1 Atlas II, modified Dana 44/60-lockers-4.10s, hydroboost/4-disc brakes, ram-assist/heim joint steering, Cage long radius arms, traction bars, 4" Skyjacker lift, 35" mud tires

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