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Misfire and crazy AFR values

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  • Misfire and crazy AFR values

    Have now driven with Pro-Flo 4 for 2 summers on my 440 and it has worked well. All of a sudden it starts to misfire and the AFR value goes completely crazy. It feels like the engine starts to go heavy and exhaust bangs arise. Has an extra AFR meter in addition to the one for the E-tuner and it reacts much faster than the one in the E-Tuner so I changed the Lambda sensor but no difference in how the engine runs. It starts well and runs normally until the engine gets warm then starts with this phenomenon. Sees nothing strange regarding values when I look in the Digital display while this is happening. What can cause this fault, ignition cables, some sensor, ECU?

  • #2
    If it's good cold, then runs bad when warm. It is some times a intake manifold will run better off idle.

    If it's running bad at higher RPM's it's some times the ignition coil going bad.

    The O2 sensor has a lazor trimmed resistor ( when you look at the plug that connects to the O2. It looks like a wire is missing ( I belive pin #7 ). If this wire doesn't make good contact in the plug/receptacle. Then the O2 sensor will miss behave a little.

    Can you post a picture of the "Digital Display", with the water temperature around 180F or higher.
    In my neighborhood, if you open your hood to check your oil, and the vehicle still runs after you close it.......Then your labeled the Neighborhood Mechanic.


    • #3
      i would check all spark plugs and wires for fouled plugs and or burnt wires . even a plug wire that has slipped back off the spark plug not falling off but is not clicked on to the end. look inside plug wire ends with a light for arcing damage i have seen center core of wire burn from loose on spark plug.


      • #4
        Put tablet on the " Digital Display " screen & take a cell phone recording, when engine is misfiring.

        Also you can spray/mist the exh tubes at the head to listen for the sizzle of a hot cyl.....A cold/dead cyl wont make a noise/sizzle. ( to find what cyl has misfire)
        Don't get too caught up in the numbers.
        Just give the Engine what it wants &
        Let the numbers be what they are.

        Jim McFarland....