Surging.

  • bacon
    bacon
    Member
    • 37
    #1

    Surging.

    My 88T with A/T recently began to surge. It started right after I added a bottle of injector cleaner. The engine speeds and then slows a little. It is mild and occurs rhythmically at a rate of about once/second. I can hear it, feel it, and see it on the tach. I replaced the fuel filter, cap, and rotor, and checked for vacuum leaks. I pulled the plugs and they all look good and checked the injector connections. I also replaced the alternator, which died within the past couple of weeks. It even does it a little when idling. I get no codes from the ECU. Also, the EGR diaphragm and FPR seem ok. Any thoughts?
  • Z_Karma
    Z_Karma
    Administrator
    • 3318
    #2
    Maybe the FPR diaphragm? If it wears out, it lets unmetered fuel into the intake through it's vacuum port. Usually if you smell fuel in the vacuum lines that actuate the FPR, it means your FPR is bad.
    I guess you could disconnect and plug it's vacuum source and see if the surging is eliminated, but it may also affect the idle. A wideband would be helpful here to see if the surging is a rich or lean condition.


    84 AE/Shiro #683/Shiro #820/84 Turbo

    Comment

    • bacon
      #2.1
      bacon commented
      07-17-2023, 10:58 AM
      I removed the vacuum line from the FPR with the engine running. No fuel leaked out from either the line or the FPR. I plugged the vaccum line and drove the car. It didn't make any difference. It ran ok but still surged.
  • Z_Karma
    Z_Karma
    Administrator
    • 3318
    #3
    Did you find this?
    https://forums.nicoclub.com/nice-93-…p-t559115.html

    I have had wonky O2 sensors in my 84T before, tho i cannot remember what the symptoms were.



    84 AE/Shiro #683/Shiro #820/84 Turbo
  • bacon
    bacon
    Member
    • 37
    #4
    Thanks for the suggestion, but I actually have two 88 turbos. One does not surge. I put an ohmmeter on the exhaust gas sensor leads on both, and resistance increased equally on the two as the engine warmed while running, which I think rules out the sensor as a possible source of the problem. It seems to be working as it should.
    Since posting I also listened to all the injectors with a stethoscope, and they all sound like they are firing correctly.
    The surging is most noticeable on mild acceleration at lower speeds. I don't see it on hard acceleration or cruising on the highway.
  • FrozenZ
    FrozenZ
    Senior Member
    • 584
    #5
    just checking, but it still happens when the car is warmed up, right?

    gonna go on because the board is so slow…

    In my experience on auto ECUs, if you don't have your idle controls or they are not working correctly, when you're below 2K RPM and between a certain temperature band on the CHTS (I think the low bound is 30C and the upper is 48C?) there's a very pronounced idle drop and surge like that after startup. Once you hit the upper bound of the temp band it stops. I've meant to see if I can find this in Nistune, but thus far it hasn't been worth the effort.

    This makes me think you might be getting stuck in this loop, and it's coming from a busted idle control. I'd try unplugging your idle controls while the car's warm and see if the surge goes away.

    If it doesn't do it when it's warm, only on cold starts, you can either try testing your idle controls to see if it matches the surging or just throw new ones at it.
  • bacon
    bacon
    Member
    • 37
    #6
    Yes, it also does it when the engine is warm. I don't know what you mean by unplugging the idle controls. Specifically, what would you unplug?