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M50NV Power delivery issues when hot

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    #1

    M50NV Power delivery issues when hot

    Background:
    - '87 325e chassis
    - '91 E34 M50NV running a 402 DME
    - Modified E34 harness originally in an '88 325is for M50 swap

    I had issues revving the car at idle or while driving, so I replaced the TPS with a junkyard unit that is in spec with no dead spots, according to my multimeter. Now the car revs at idle fine, but if I am driving, it sputters. This behavior only occurs once the car is out of cold start. I have another tested & good TPS as well as another tested and verified good MAF on hand. I sprayed carb cleaner around everything intake related in small sections to check if I had a vac leak, but the intake tract seems to be sealed. I also used a smoke bomb as a ghetto smoke machine test, and I have zero leaks with that on the intake and exhaust sides.

    My guess is that my oxygen sensor is getting lazy. What else might cause this problem? The spark plugs are 7 mile old NGK BKR7Es. This is the only thing keeping me from daily driving the car again, so any and all constructive help would be appreciated!
    Tags: None
    #2
    Does it feel like it is misfiring? Coil pack could be going bad they get worse with heat.

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      #3
      I swapped coils with my roommate's M50NV and saw no change. I read in another thread that the car should run, if marginally rough, with the oxygen sensor disconnected, so I gave that a shot. Turn out disconnecting it means it drives without those power hiccups, so I'm getting an E34 oxygen sensor today.

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        #4
        You are running the M50NV MAF right?

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          #5
          Correct; I have two that test fine via the Bentley's specs.

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            #6
            Car runs fine with the oxygen sensor disconnected, but it still has the same issues with the new oxygen sensor. The green and violet wire in my harness is hot to the touch, as my roommate discovered; this is for fuel pump power. Unsure of what else could cause this problem.

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              #7
              you can try this:
              http://www.r3vlimited.com/board/showthread.php?t=192533&highlight=o2+sensor


              no guarantees though. there are very mixed feelings about the validity of this mod. I think it made a difference for me, but now since its been a while i wonder if it was all in my head...

              Comment

                #8
                Thank you for everyone whom contributed! Shiboujin fixed it by adding two new grounds and installing ground plates for the coils off his M50. I owe him those plates, and life is good.

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