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Thread: 7AL3 intermittent misfire

  1. #1
    Join Date
    Feb 2018
    Posts
    3

    Default 7AL3 intermittent misfire

    Gday. I have a 7AL3 that has just started with an intermittent miss fire. It has a crank trigger and is using the pro power coil. The missfire appears after 6500 rpm. Since starting to try and diagnose have also identified that the phasing of the distributor is changing as motor warms up. Running 38 degrees timing distributor locked (welded)so figuring something else causing timing to change therefore affecting phasing. Mag pick up not moving, reluctor wheel is not moving. Am out of ideas. Cheers Nick

  2. #2

    Default

    Which 7AL3 are you using is it the older red box or the newer black box?

  3. #3
    Join Date
    Feb 2018
    Posts
    3

    Default

    Newer black box

  4. #4

    Default

    Where is the ground for that box going? Also the mag pickup wires are they isolated? If you heads are aluminum do they both have a ground strap?

  5. #5

    Default

    Also, how long are you running the motor for?

  6. #6
    Join Date
    Feb 2018
    Posts
    3

    Default

    Gday mate. It goes direct to battery. Engine is in a drag car with solid mounts. Car was running for 5-10 minutes. This has been in car for about 3 years and been fine. Problem arose in one pass with it missing twice on second gear then was fine. Next pass burnout was fine (6500 on limit) but then miss fired at top of 1st gear (7500) then another 4 times whilst going down track.

  7. #7

    Default

    Ok, so if all the grounds are good, and the motor plate is grounding your heads, and the mag pickup wires are isolated, then what I would look at doing if you haven't done this is to try another coil if it is also 3 years old. Because, from what I have seen on those 7AL3s is that when they go bad they just quit firing. Usually, a misfire at higher RPM and sometimes lower RPM is caused due to noise interference on the mag pickup wires, a bad ground, or a coil going bad.

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