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Lurching on acceleration above 55 mph

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  • Lurching on acceleration above 55 mph

    I'm back. My Z is an 88T with A/T. The turbo trans failed so I picked up an 86 non-turbo trans and had a shop install it. It turned out the torque converter was bad in the nt trans; it had a terrible case of TC shudder; it felt like driving over railroad ties as the TC approached lock-up around 45 mph. I got a used TC on Ebay and installed it. The trans shifts fine and the shudder at lock-up is gone, but at about 55 mph when accelerating the car lurches or jerks. It feels like stepping on and letting off the gas about once/sec. It is completely different from the TC shudder; much less violent and the car does not shake like it did before. I can see the tach rise and fall a little with each cycle of jerking. It did not do this before the TC swap, and the TC is the only thing that was changed. It only does it in OD and it does not do it at steady speeds. It accelerates, shifts, and runs fine until it gets to 55 mph; then the lurching starts. The trans fluid is clean and new and no junk was in the pan when I swapped the TCs.

    I have described the symptoms to three different mechanics and they all think it is more likely an engine than a TC issue. They all suggested it is most likely caused by a misfire under load. I am not getting any codes from the ECU. I swapped the plugs, plug wires, distributor cap and rotor, AAC valve, air regulator, and MAF with known good ones with no change. I replaced the fuel filter with a new one. Fuel pressure is 38 psi at idle with the fpr vacuum connected and 45 psi with it disconnected. The fpr is not leaking gas. With a stethoscope I can hear all the fuel injectors firing. I have checked carefully for vacuum leaks and it is tight. Like I said, I didnít do anything to the engine; the only thing changed is the TC, and it never did this before.

    Is there any way this used TC could be causing this symptom at this speed once it has locked up, or does everybody agree it is more likely to be an engine/fuel issue?

    Sorry for the long post but I wanted to supply all the details and describe everything I have done to try to fix the issue.

  • #2
    If you have an AAMCO transmissions near you, they can diagnose if it's a transmission issue.

    If you think it's an engine issue, look at your RPM, not your speed when it starts lurching, then turn OD off and bring it up to that rpm in 3rd and see if it does it. You could also put it in 2nd and do the same.


    • #3
      Dunkine, I appreciate your input, but AAMCO? Really? I made the mistake of going to AAMCO once. Never again. If you had a headlight out they would diagnose it as a transmission issue, and when they were done your headlight would still not work, but they would bill you $3,000.

      I have driven with the OD turned off. The jerking only occurs in OD.

      As an added piece of information, tonight I discovered that the jerking also occurs with the lockup solenoid disconnected.


      • Dunkine
        Dunkine commented
        Editing a comment
        Heard nothing but good things about the Aamco up my way. I just stick swap'em, problem solved, well, if it turns out to be a trans issue

    • #4
      Check your plug wires and make sure there fully seated


      • #5
        One thing I did was to install a small AT filter before the radiator ... The clutch material creates sludge in the transmission and fouls the at body and solenoids ,,,
        After sitting for 2 years the lockup solenoid wasn't working ...I also added Auto-RX to the trans ... after adding the filter it came back fine .


        ATP AT IN-LINE FLTR 5/16
        Part # JX-150

        Last edited by dbruce; 11-07-2018, 11:55 AM.