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Thread: Misfire under accel, right bank rich - left is lean

  1. #1

    Default Misfire under accel, right bank rich - left is lean

    My car has been running pretty good up until last week. When I tried to do a burnout it acted like I had traction control (bogging the engine down) so I went to pull away and had a dead cylinder. Got it home and cylinder 8 had a totally open circuit spark plug wire. Also checked the plug and it still appeared good. Put a new wire on and all was good, ran fine, idled good. The next day went to drive it and got a couple blocks away, had the misfire/dead cylinder again (same side of the engine). Got around to checking the wires today and all are good.

    When cruising at one speed the engine runs good, a/r ratios match on each side.
    While accelerating the left side is considerably leaner.

    In my mind either the left side has an issue with a fuel injector not firing or partially plugged, or the right side has a poor spark that is getting blown out under a load.

    Does MSD have any way of letting us look into the efi system with a laptop or data log to get more information?

  2. #2


    I swapped the drivers and passenger side coils, ohmed out all the spark plug wires, installed new plugs, ohmed out the two coil pack harnesses, have proper voltages and grounds going to them too. Did a compression test while the plugs were out, 175-190 psi. Car still runs like crap.

    Is there any way of forcing the injector to pulse one at a time with the MSD setup? On my last project car I could do almost anything with the efi system it had (disable spark plugs, change firing order, force the outputs one at a time...)

    I am still not sure what is happening, either the drivers side has a fuel delivery issue (the fuel pressure is constant though) or the passenger side has a spark/ignition issue.

  3. #3


    Swapped drivers side and passenger side fuel injectors this morning, still have the same issue. The issue starts about 60 seconds after initially starting the engine during warm up. Called MSD and they said there is nothing else I can do with it, have to send it in for testing so I got the RMA and address.

    FYI, these units are non-repairable. One person I talked to on the phone said they can sell me which ever item has failed, the other person said they can't. I am hoping when we know which piece has failed that we can get just one replacement part.

  4. #4


    Joe, have you got this resolved?

  5. #5


    That is a negative. Talked with MSD support and they said that everything I already tried and tested was all I could do and to further look into it the system will have to be shipped to Texas. They should have received it August 11th or 12th. I am still waiting on a response back from them, as far as I know they have not looked at it yet.

  6. #6


    To update everyone, MSD tested the unit and it doesn't look like they found anything wrong (at least its not mentioned on the paperwork). I have since installed a different EFI system and it appears to have the same issues with randomly running lean on the drivers side of the engine. I have tried to find vacuum leaks with carb cleaner, brake clean and propane with no luck. I am starting to think about pulling off the intake manifold and checking the seals on it, perhaps look for cracks or a broken fitting at the back of it.

  7. #7
    MSDTECH80 Guest


    Have you performed any type of testing on the motor?
    compression or leak down test?

  8. #8


    Completed a compression test before I sent the system in, I believe they were 185-195 or 180-190 PSI, I cant remember because it was a couple months ago already. Did a leak down test a few days ago, most cylinders were around 4% and the worst was 8% on the gauge which was still in the green part and in the manual says its ok.

    Also tried to find vacuum leaks with a smoke machine, this showed no leaks. Pulled the intake and the seals looked good, nothing folded over and no evidence of leaks. Intake doesn't appear to be cracked anywhere. The brake booster vacuum line was a 3 piece unit to make it fit, I have tested this after I removed it and no leaks but I did more searching online and found one that is one piece and will work.

    Pulled the exhaust headers and the gaskets to the heads were still sealing good, I have new ones to install. I also couldn't find any evidence of cracks in the headers. The O2 sensors were previously located downstream of the collectors a few inches due to chassis clearance issues. While the headers were out I relocated them into the collectors.

    I am putting it back together today and hoping to start it up tomorrow.

  9. #9


    Its back together and runs the same. Someone stopped by yesterday while I was working on my car and said he has similar issues in the past with an engine and it had a cracked valve spring. I did some searching today and seems possible. While it was running today I was watching the MAP sensor, it fluctuates up and down but only does this when the engine is going lean. When the engine runs good and both sides have matching a/f ratios, the vacuum is steady. Going to look into this some more.

  10. #10


    Do you have a laser temp gun? can you check each cylinder and see which is giving the issue? Just a thought so you can narrow it down to one cylinder or 2.

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