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Thread: Misfire? under load after 2000 rpm, persists until restarted 95 3.4l Camaro

  1. #1
    Newbie notsonic's Avatar
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    Misfire? under load after 2000 rpm, persists until restarted 95 3.4l Camaro

    I have a 95 3.4l Camaro. It's got 220k on the body but the engine is a pull out from another 95 with around 80k on it and has been in the car for a few years.

    Some background: I took my car to its first track day and during the third session I lost power exiting a corner. I thought it was a misfire, did some basic diagnosis, and everything seemed fine. Got on the track again, same issue.

    What seems to be happening is the car will start, idle, and rev fine. When it's in drive if you stay under 2000rpm it's fine, though it's really difficult to do this so I haven't been able to see if it's a open loop startup related thing or not. As soon as you go over 2000rpm in drive it will studder and continue to do so at any rpm until restarted.

    I have change the plugs, wires, coils, icm, pcm, 7x (3x? the one on the passenger side of the block) crank position sensor, and map. It behaves exactly the same.

    When changing the plugs i noticed 1/3/5 look normal to lean and 2/4/6 look rich, with 4 being wet with fuel or oil.

    In researching this problem I've seen people suggest injectors, fpr, fuel filter, and fuel pump. I'm willing to do those, but if anyone has any insight on how to diagnose this it'd be greatly appreciated. I've also seen the camshaft position sensor and the 24x crank position sensor suggested. I'll try those as I still have the ones from my 220k block and that ran fine.

    EDIT: I've done additional testing to confirm that the misfire happens just after 2000rpm in drive. It does not happen in park or neutral. I can put it in drive and do a brake stand and once I hit 2k it misfires.

    EDIT 2: I have a Tunercat/Datacat cable and tried monitoring it with Datacat and to be honest I have no idea what I'm looking at. The knock count doesn't go up, retard stays at 0, and my spark advance hovers around 20-30. I have no DTCs and I THINK all the bits are normal but I can't say for sure. The only thing that seems suspect is that the 6x ign value stops after 2000rpm. Is this normal? Is there anything specific I could be looking for with Datacat?
    Last edited by notsonic; 06-27-2018 at 05:26 PM.

    1995 3.4l v6 camaro
    mostly suspension

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  3. #2
    Full Throttle Extreme!
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    How about a clogged cat? Very easy to check and sounds like your symptoms.
    http://www.misterfixit.com/cat.htm

  4. #3
    Newbie notsonic's Avatar
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    I think my cat is fine, it's older but it's a high flow Magnaflow.

    I used Scan9495 and found the "injector failure this run" flag was getting set when the misfire occured. I confirmed with a stethoscope that the injectors were being shut off. I rebuilt the fuel rail with 6 new injectors and regulator and it seems to be back to normal.

    So if anyone sees this, once an injector fails the computer shuts it off until you turn the car off and on again. It does not set a check engine light. In addition it won't have the rich smell of a no spark misfire since the offending injectors get shut off.

    1995 3.4l v6 camaro
    mostly suspension

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