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Thread: RPM dancing, poor driveability, help!

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    RPM dancing, poor driveability, help!

    I have a 1991 3000gt vr4, 117k miles, bought it with a lower end rebuild 500 miles before i bought it.

    drove car home after driving, it. eventually got a logger installed, noticed that my rpm seems to go up and down, in idle, during cruise, even in wide open throttle the rpm will drop sometimes before going up. this feels more like a loss of power, than a bucking motion.

    It has a slight misfire at idle.

    I had found a front o2 sensor harness smashed, but i think i may of mixed up a couple of the wires when i put a new plug on it. front 02 sensor was reading .2v even when full warmed up, and not fluctuating. fixed the 02 sensor wiring, still getting hte same reading, i may of sent 12V heater power, to the sensor ground circuit, never smelled anything smoking but may be damage somwhere, rpm fluctuation existed before i messed witht he o2 sensor and still exists though.

    The o2 sensor wouldn't effect warmup or wide open throttle, so i don't think it's the culprit to my rpm fluctuation(rpm goes up and down like 10 times a second constantly)

    during warmup, my o2 sensors read lean, then work towards rich, the wiki says they should start rich, and work towards lean before fluctuating back and forth once warmed up. My rear o2 will start fluctuating, but my front o2 just holds a steady voltage.

    with car in run, without the engine running, my 02 sensors both read 0.03-0.05v.

    I also checked my plug wires, they are bosch, all have continuity, though the resistance is much lower than stock, could these be a problem, the wires themselves are in good condition.but only 600 ohms per foot, instead of like 4500+ ohms per foot of stock wires.

    I've got ngk coppers heat range 7 gapped to .028, car has 19t turbos on it, running on wastegate pressure of 11psi.

    I'm just not sure where to chase this problem from, don't wanna just start smacking it with the purse, i'll end up parting it if i can't figure out how to fix it. any help appreciated!

    I can attach a warmup log if you'd like. actually file size limit is 100kb so i can upload it somewherehttps://datazap.me/u/kruqnut/more-cr...p?log=2&data=8

    Oh, also about the car, has vacuum delete, no EGR or Purge at the moment.
    Last edited by kruqnut; 03-03-2018 at 02:42 PM.

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    I guess what I'm asking, if you were a proper service shop that knew about 6g72tt engines, what would be the troubleshooting procedure to figure out what is wrong with the car?

    I have checked plugs, put new copper NGK heat range 7 plugs in, gapped at .036, .032, and .028.
    I have checked the spark plug wires for cracks, checked the resistance.
    I have checked the harness on the CAS, and on the MAF. I have tried swapping mafs.
    I tested the PTU and also tried swapping one.
    I pulled apart the ECU and checked caps, they were good, I replaced with a chrome ecu anyways.
    I disconnected the ECS computer.
    I replaced the injectors, with 560cc evo injectors, set the values and latency in chrome, and flashed it.
    I replaced the injector connectors.
    I did compression check on cold engine, 135 even on all 6 cylinders with a cheap harbor freight gauge.
    I replaced the intake, lower intake, throttle body gasket, and biss screw 0 ring.
    I sprayed starter fluid heavily on every connection while car was running and had no change in rpm besides the fluctuations.
    I put pressure into the intake system and it holds some pressure, though not much, extra pressure seems it is leaking thru the valve cover, as i noticed the cap bobbing up and down when i had it slightly loosened. I haven't isolated the intake anywhere to try to avoid sending air into the engine in order to pressure test the piping and turbos etc outside the relief from the crankcase.
    I checked timing, adjusted CAS to 5 degrees.

    After this log I re-set the idle, the best I could with a fluctuating rpm.

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    bump for help!

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    daily bump for help

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    You're bumping a post that is already sitting at the top. Stop. No one is around on the weekend. People will answer when they see it.

    [06-05, 19:29] OhioSpyderman: Brian, finding a woman is NOT the answer, you need to shop for a good VACUUM

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    i haven't backed out of the forum, i just have the page loaded, is it hurting anyone? i waited almost 24 hours to bump it

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    The point on a BUMP is to BUMP it to the top of the page. When it is already sitting at the top of the page it is a wasted post. It will stay highlighted as a new post until it is viewed.

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    Well, what I see in that log is your front O2 is dead and your timing is jumping everywhere.

    Step 1 is to fix a misfire if you have one, you can't move on to anything else until the car will idle correctly. I don't know what a "slight misfire" is, you either have it or not. You'd have better luck unplugging both O2 sensors during your diagnosis and running it in open loop.

    Also, 135psi seems low to me, I'm used to seeing 155 psi.

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    Yes I know the front o2 is bad, i had this problem when it was still working but on a smashed connector. Also the log is open loop, as the engine is still cold in it. The rpm fluctuating exists in open and closed loop.

    It misfires lightly every 10-15 seconds once or twice. the RPM fluctuates much faster than the timing changes in the log, but maybe i can get a more precise timing value to log? I would guess its misfiring because the engine is stumbling so much and it can't compensate for the rapid rpm fluctuation.

    I tested the compression cold, on a cheap gauge, it was exactly the same on all cylinders, i don't know what would cause an even compression loss on all cylinders evenly, I took the consistent reading as solid, the manual said 115psi was the minimum for a TT engine.

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    besides the o2 sensor, if i'm having problems in open loop, what do i check?

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