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Thread: 7 AL3 miss fire at 2800 rpm

  1. #1
    pylavigne Guest

    Question 7 AL3 miss fire at 2800 rpm

    :glare:Hi , i have a chevy nova 1974 . My msd 7al3 box is located in the trunk. I have twist the violet and green wire together all the way to the distributor . My coil is hvc2 hide over the glove box . I have a pass trought connector in the firewall for the spark wire to the distributor from the coil. Maybe some wire whit 12volts touch the violet and green wire. The engine miss fire at 2800 rpm . It is really the violet and green wire touching 12volts or passing near the coil my problem? Everything is new. On the dyno the ignition box and coil was not mine but the distributor was fine. (A msd distributor). Thanks

  2. #2
    pylavigne Guest


    Do I really need to put a zero chip in each retard step? There is only a chip in race ....6000rpm

  3. #3
    MSDTECH80 Guest


    What is the total timing on the motor?

    The motor will not rev up over 2800 rpm's, is this in gear or just free revving?

    If you don't install 0* chips or ground the 4 retard terminal, the box will retard timing up 20* at any rpm's.

  4. #4
    pylavigne Guest


    The best timing on the dyno was 39* . The engine can go over 2800rpm . On hard acceleration it goes right up to 2800rpm and popping for 2 or 3 seconds and after the acceleration continues to 6000 rpm. On smooth acceleration it goes well until it its 2800 rpm popping until I get around 3000 rpm after it go well. If I stay at 2800 rpm it feel like the fire don't know on what feet dancing. On free reeving it popping at 2800....

  5. #5
    MSDTECH80 Guest


    Ground the 4 retard terminals, where is the violet wire hooked up to M+ or M-.

  6. #6
    pylavigne Guest


    PROBLEM SOLVED:001_cool:. I did a new harness for the distributor. (Violet and green wire). I route it over the car to make a test . The first time a start it whit the new harness , the problem was still there but I realized that the wire was on the coil spark wire. I move the harness about 4 inch away from the coil spark wire and problem went away. Now it smoking tires. :thumbup1:

  7. #7
    MSDTECH80 Guest



  8. #8
    Join Date
    Jul 2003
    Seattle, WA


    This isn't the first time someone has had trouble with the mag pickup wires, but I think the first installation with these wires running to the trunk. The signal level on the mag pickup wires is very low and in any case will not work when tied to the coil wire. I would use shielded twisted pair wire in this application, making sure that the 7AL ground wire runs to the battery, and grounding the shield (above) to the battery only. That's what I'd start with anyway.


  9. #9


    My 7al3 has been doing the same thing. Checked all the wire connections and ohmed everything like the trouble shooting guide says. Only thing I have noticed is on the battery + and - I have 12 volts same with the ignition wire. When the engine is running it shows 18 volts for a split second then I can't get a voltage reading at all on those screws.

  10. #10


    please start a new thread with your issues.

    can you please give me your battery specs

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