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Random Bogging and Backfiring

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  • Random Bogging and Backfiring

    If someone can help, I would appreciate it.

    Case in point:
    1987 Nissan 300ZX 2+2 GLL Auto-->5spd conversion.

    Problem at hand:
    During random times whether it is around my neighborhood, or during highway travelling, with speeds excessive if you catch my drift. I get a popping sound through the exhaust like backfiring (only on downward rpms), I try and give it some gas and it starts to bog down and I go from 65 to 45 and then all the sudden it revs back up for a bit and then it does it all over again. BUT, I sometimes can work past it by stomping it and passing 65mph and have a 50/50 chance of the problem reoccuring. Also when the backfiring happens, if I was to stop, the idle would reach 0 and kill the motor.

    If it happens when I am near my house, I make it home carefully and park it. About 2-3 hours later, it starts up no problem, and idles decent about 700-750.

    Vacumm readings
    during normal idle show steady 25 or 26.
    During the freak show of embarassment 20 through 27.

    Fuel readings read on both normal idle and wierd idle 25-27psi, if I pull the vacumm line off the FPR, it hits 40psi. I have a summit inline FPG.

    Items I have installed or replaced since I bought my Z a year ago.
    BRAND NEW CHTS and Harness
    NGK sparkplugs
    Nissan rebuilt Distributor
    NUsed FPR (looked new)
    NUsed Air regulator on side of intake
    Cone filter and all elbow are connections tight
    NUsed TPS (connection tight)
    NUsed AFM (connection tight)
    Cap & rotor
    All vacumm lines
    New alternator
    New battery and terminals
    Ford taurus cooling fan w/ adjustable thermostat
    O2 sensor
    Auto to 5spd swap
    and more

    I tried running codes, but the results I get do not match the results that everyone tells me I should see.

    When she runs good, man she runs real good, when she is bogging, she runs like crap.

  • #2
    This could be a long shot cause its been a while since i've dicked around with a stock z31 but it sounds like maybe you are running too rich under deceleration caused by the cylinder head temp sensor.

    Anyone else got a different idea? Maybe the aftermarket FPR is screwing with stuff?

    Either way it sounds rich under decel.
    85 Z31 6.0 LSX turbo 766whp/792wtq
    04 GTO, LS6, big cam, porting, N20... underway for summertime daily driver.


    • #3
      Do you still have the Auto TPS in there? May also be a long shot, but maybe there are some spots going really dead. Really long shot

      Terrible idea putting those wheels on...


      • #4

        I took a look at my CHTS wiring and found that the wires are corroded and cracked on the engine wiring loom side. I am going to cut off the connector and solder in some new wire, see if that helps.

        NUsed = new to me but its used. JunkYardSpecial

        The TPS, I have one on from a 90's maxima, also used one from a 84 that looked newer than mine. It was better with my old auto one I had.

        question when adjusting the TPS. I built a test kit that lights a LED when you turn the TPS to show the connection has been made. Do I leave it right where it is when the light turns on? or when it first turns off?


        • #5
          ^ First turns on.
          imagination is a virtue