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firing order / and a miss

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  • firing order / and a miss

    Does anyone know the correct firing order for the 3.4 DOHC?? For what I know it's 135 for the rear bank passenger to driver and 246 for the front bank paseeenger to driver side. Is this correct?

    I had my crank sensor go one day and the car would not start. I've since replaced it but it has not run right since. It won't rev over 3000 without bogging and backfiring through the intake. I put a new ignition module on that I bought from canadaian tire ( not a delco ) and it seems to have an ignition miss. I purchased a new delco ICM from GM for double the price and it won't start with that one in. It's like the plug wires are mixed up. I triple checked the firing order with no luck but as soon as I put the ICM from canadian tire back in it starts but with a miss and no power again.



    heres a list of the parts I've replaced since this started

    Idle Air Control Valve
    New Plug Wires
    New MSD Coils
    New Ignition Module ( I currently have three) original - non delco - delco
    switched computer from 92 Lumina Z34
    New fuel Filter
    New Crank Sensor
    Removed plenum and lower intake installed new gaskets to rule out vac leak
    New Knock Sensor
    1991 Pontiac Grand Prix GTP / 3.4 DOHC

  • #2
    i belive you have the order correct, make sure your icm and coils are mounted securely they ground through the mount and if they vibrate thats not good for the ground.
    If you aren't friends with a liar, you aren't friends with anyone.

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    • #3
      I had thought that the ICM mount needs to be grounded to the engine as well as the power supply harnness. It doesn't. Today when I put the new delco ICM in and it didn't work I put the non delco ICM on top of the airbox to test it against the new one and it wasn't grounded at all. My car still started.

      I tested the original ICM that was in the car when I bought it. I thought it was toast but it still gives the car an initial fire and then the engine just turns over and farts a bit.

      I guess I'll have to swallow my pide and take it to the GM dealer to get an analysis done on it. I just hope they can get the new ICM to work in the car instead of the other non delco. Otherwise im out $400 cdn.
      1991 Pontiac Grand Prix GTP / 3.4 DOHC

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      • #4
        make sure that your wires are connected well to the ICM. THey might plug in, but are the wires in the harnesses snug on the pins in the ICM?
        92 cutty auto with a 97 3.4

        93 convert with 3.4

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        • #5
          connections

          Yes they have clips that hold them in place and either they're on right or ready to fall off. I did extend the wiring about two feet put the module where the battery usually goes (relocated to trunk). I soldered the connections and tested them with an ohm meter at the ECM so I know they're solidly connected. none of this explains why a delco ICm won't even start the car and an off brand will. I can't figure that out.

          The crank sensor I replaced from the one that was dead had a shorter head but the sensor length was different. My Pontiac dealer insisted it was the right one though.
          1991 Pontiac Grand Prix GTP / 3.4 DOHC

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