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Ye Olde 4000rpm stutter - FIXED

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    Ye Olde 4000rpm stutter - FIXED

    So I have hit all the things I can think of. This story actually starts over a year ago, when my ix developed this stutter and it progressively got worse. In fact, it may have had a 4000rpm stutter and then it acquired a new stutter that promptly got so bad I couldn't drive the car.

    I swapped:
    AFM
    TB/TPS
    Engine Harness
    DME
    CPS
    Injectors
    Cap and Rotor
    Ignition Coil
    Ignition Wires
    (maybe some other things)
    and then the item that actually fixed things, The Harmonic Balancer that the CPS reads off of.

    But it didn't fix it 100%. I've lived with it for a year now and decided to chase it again. I thought maybe the distance of the CPS is off, but that thing couldnt be any closer to the balancer. Unless we're talking valve clearance levels with a feeler gauge.

    The CEL comes on, it only happens at full throttle. I don't need to lift, it's a momentary hard jerk and then it keeps pulling. The engine pulls hard. It's not consistent. Last Saturday on 20ish WOT pulls, it only did it on first one. Today it did it on all of them. Today I replaced the injectors, the dme, and the afm again. No change. I unplugged the O2 sensor and TPS, also no change.

    I swear it has to be an inconsistent ground or electrical connector somewhere, but hitting random things does not change anything.

    Searching does not produce anything that I haven't already tried. But still, please throw your ideas at me.
    Last edited by Kershaw; 10-05-2016, 09:27 PM.
    AWD > RWD

    #2
    O2?
    1986 LTW M52 (First project 2015- )
    1998 e36 328ic/5 -
    Roundie alpina pig cheekā€™d (1969)
    1967 2002 parts car
    1994 318iS junked.

    Comment


      #3
      Have you checked fuel delivery per Bentley (not pressure)

      Sounds exactly like my 325i before my pump blew

      Comment


        #4
        I know you said you replaced the engine harness, but was it with a new one?



        TLDR?

        jlevie put 3 used engine harnesses in his car for a similar issue to yours and none of them fixed it. Only a new harness was the solution. Might be worth getting a cheap oscilloscope and checking the CPS signal like he did. You can get an oscope for a hundred bucks on Amazon these days.
        Last edited by Cephas; 11-18-2015, 11:32 AM.

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          #5
          Fuel pump is a 2 year old 255lph unit. I can't remember if I swapped that last year. I'll check it again.

          It was not a new harness, but it was a working harness when it was removed. That said, maybe it's worth buying a new harness. I don't want to know what an IX specific harness will run me. Isn't a new CPS $60? This CPS was new when I put it in last year.

          edit: Maybe I can pull my engine harness and duplicate a new one... After reading more of Jim's saga (and our past PMs) I really think I have the same issue as him. It's persistent and consistently pops up no matter what else changes. Thanks for that link, it made me remember his PMs from last year when I thought I had it fixed.

          edit2: It seems that this issue is only related to the cps wiring on the engine harness. Maybe I can just replace those wires. I might give that a shot this weekend.
          Last edited by Kershaw; 11-18-2015, 02:17 PM.
          AWD > RWD

          Comment


            #6
            Updates: I think I fixed it but I've said that before.

            12/9/15: I replaced the CPS and routed it properly. I had my old CPS (which was new last year) mounted over the distributor, next to the pulse sensor. I thought maaayybbe I was getting some sort of interference at specific frequencies. So I routed it properly and zip tied it back because I don't have that cover in place. I started it up, drove it for 10 minutes, it ran great, I thought the problem was fixed. A few hours later, after rush hour died down I took it out onto some back roads. Immediately the problem was present again. Fffuuuu

            12/10/15: I replaced the harmonic balancer, fuel pump relay, and alternator/ps belts. Also I ran to Home Depot to buy new bolts and I ended up buying a new shop vac. Home Depot, not even once. Took it out for an extended 30 minute back road drive. Drives great, but a CEL does come on. However, it's still running the 380 DME/matched AFM with a basic turbo tune on it, so I'll be putting my 173 and old AFM back in today. But I think this issue is finally fixed.

            Items it took:
            3 engine harnesses
            3 CPS
            3 harmonic balancers
            4 DMEs
            3 AFMs
            1 fuel pump
            1 fuel pump relay
            8 cans of brakekleen (cause hey, if you're in there...)
            1 alternator belt
            1 power steering belt
            6 m8x16 bolts
            4 m6x10 bolts
            4 m6 washers

            And I'm sure I probably missed a few items. To conclude, I am not actually sure what item or combination of items fixed the issue.
            AWD > RWD

            Comment


              #7
              Update 12/11/15: not fixed.

              Fuck everything about this.
              AWD > RWD

              Comment


                #8
                Is your CPS an OE or OEM unit?
                Lorin


                Originally posted by slammin.e28
                The M30 is God's engine.

                Comment


                  #9
                  Yes.

                  I think it's just time for a different engine management solution.
                  AWD > RWD

                  Comment


                    #10
                    We should get together and compare 4k stutters.

                    Instagram: Reichart12

                    Comment


                      #11
                      You missed the meet yesterday!
                      AWD > RWD

                      Comment


                        #12
                        I realized that every time the car ran well, the battery had been unplugged for awhile. I don't know if that means anything, but I'm writing it down to document it. I'm going to try reground as many things as I can. I'll try to test this theory soon.

                        Anyone know why adding random grounds would be bad? Like strut tower to valve cover or something similar.
                        AWD > RWD

                        Comment


                          #13
                          You and me both except my stutter is randomly at all RPMs, sometimes making it undriveable. My problem started a year ago this month. The car was cutting-out/stuttering (a bit worse than now) so I changed the fuel filter and that fixed it... apart from a very rough idle on warm starts. After a while, the stutter started developing again to the point I'm at now where I can't drive the car. The idle is really bad when cold and when warm, sometimes even stalls and doesn't turn on unless I give it 3-4 cranks. I've changed: timing belt, tried on 2 AFMs, changed fuel filter twice, fuel pump, spark plugs twice, distributor cap and rotor, O2 sensor, intake boot, some fuel lines, and the car has absolutely no vacuum leaks (just checked today). I'm out of options at this point. I'm getting like 8 mpg highway so it's not like I could just ignore the problem. I'm as stuck as you are... I gave it to a mechanic today and he tweaked around with some shit, patched up any vacuum leaks there could be and took out all the front pulleys belts and tweaked around with the timing. The stutter is (apparently) gone but the idle and mpg are worse than ever.

                          Comment


                            #14
                            Maybe unrelated but how about an engine temp sensor. Hard to get to without pulling the fuel rail but is something the dme relies on to determine fuel.

                            Comment


                              #15
                              Originally posted by uturn View Post
                              Maybe unrelated but how about an engine temp sensor. Hard to get to without pulling the fuel rail but is something the dme relies on to determine fuel.
                              Changed that too

                              Comment

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