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S50 vibrates power loss above 4.5K

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    S50 vibrates power loss above 4.5K

    So my S50 idles and runs well. It's totally driveable around town. No codes.

    But with heavy throttle (WOT and lots of part throttle), it losses power and starts to vibrate violently above 4.5K. It is intermittent, sometimes it pulls hard and fast to redline.

    I was doing pulls on the freeway tonight to better characterize it and that seemed to exacerbate the problem because for the next 15-20 seconds it would stumble with even light throttle application.

    Things that I think could be related:
    -Big K&N filter directly on the MAF
    -Bad O2 (but I read that it goes into open loop at WOT)
    -Bad fuel pump (it's an Eta and the pump under the car is noisy)

    It has new OEM Bosch copper plugs, I think the ECU temp sensor is working, stomp test works so TPS/WOT switch seems to work, idles well so I don't think it has a vac leak, rebuilt 17 lb injectors.

    It's running on a 413 Red label ECU with a 506 tune with EWS deleted. I experienced the same problem on a completely unaltered 413 Red so I don't think it's tune related.

    I searched and didn't get much...
    Last edited by M3PO; 07-11-2014, 12:10 AM.

    #2
    I'm guessing something to do with the VANOS unit
    '87 325ic, powered by S50.

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      #3
      Little bit of an update. I drove it to work and it doesn't seem to do it when the car is in open loop (ie when it's cold and at WOT). I thought I was WOT last night but maybe not. I think the floor mat was in the way.

      That points to a bad O2 sensor.

      I'm also getting an occasional miss at idle.

      I'll report back when I change the O2 (have a few laying around).

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        #4
        No change with the "new" O2 sensor.

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          #5
          My guess would be a bad coil. When your putting the car under load the coil keep up. Check all your boots for cracks. If the boots have cracks the ignition can leak out and not get to your spark plug.

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            #6
            My vote is for bad coil too. I had a misfire problem that only happened under load on my E36.

            Originally posted by ROLLingKING
            i have a bronzit and plan on making it look sweet.
            Originally posted by slammin.e28
            Moral of this story?

            If you drive your e30 on stairs, you're gonna have a bad time.

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              #7
              sounds like a fuel starvation issue to me. what kind of mods have you done? do you need bigger injectors?
              o2 sensors would only really throw a code. (and only affect fuel mileage)
              vanos units will only make you lose torque and possibly hear a rattle in the engine bay. (if its binding, it will also throw a code)

              I would looking into your coils or injectors
              PNP Adapter Harness Wiring for M52TU, M54, S54, M60, M62, M62TU, S62, M50, S50, M52, S52 & MORE

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                #8
                I looked at the coils and plugs. All of the plugs look good. One coil has a cracked boot but all others "look" good.

                The injectors are all freshly rebuilt. The car has headers and a cone filter (in the engine bay), no other mods.

                On a side note, oil can only get into the plug wells if the valve cover gasket is leaking right?

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                  #9
                  Something I forgot to mention. When I got my S50, someone had cut the MAF plug off. So I soldered a new one on. It runs like shit without the MAF plugged in so it seems to be working okay.

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                    #10
                    I've got a slight miss at idle. Occasional pop. I pulled each coil plug with it idling and every cylinder sounded the same.

                    I tried a 413 red with an M50 chip in it and that seemed to help the miss at idle but not at high RPM. It still falls on it's face.

                    Comment


                      #11
                      free things to try...

                      disconnect 02 sensor and see if it still does it.
                      then disconnect temp sensor and test it out.
                      disconnect VANOS plug and try it out
                      '87 325ic, powered by S50.

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                        #12
                        Just an update for everyone. A new-to-me set of coils seems to have solved my problem.

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                          #13
                          Well, I sort of spoke too soon. It pulls all the way to redline nicely now but I've still got a miss at idle (every couple seconds) and maybe up to 2500-3000 RPMs. Any ideas what would cause this?

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                            #14
                            Little update: cleaned the MAF and the ICV and the problem is still present.

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                              #15
                              Just to update this, changing the plugs from Bosch coppers to NGK Platinums solved my misfire at idle.

                              BUT, now I have a new problem. The car pulls like crazy when cold. Spins 1st and 2nd no problem. A couple minutes in, it will lose a lot of power and barely spins at the top of 1st. It runs beautifully, it just doesn't have the power that it should. It pulls better above 4K (VANOS related?) but is still slower above 4K than when cold.

                              -S50 with 114K miles
                              -ebay headers
                              -custom cold air intake
                              -great idle
                              -runs like crap with MAF unplugged
                              -runs like crap cold with coolant sensor unplugged
                              -noisy fuel pump
                              -dead aftermarket cat
                              -new OEM cam sensor
                              -new platinum plugs
                              -used coils (tops have cracks), new boots
                              -rebuilt injectors
                              -MAF plug was cut off my harness, soldered new one on
                              -cleaned MAF
                              -tried three O2 sensors, all the same results
                              -no vacuum leaks (I think)
                              -crank sensor ohms out correctly
                              -VANOS rattle at ~2500 RPM on engine braking
                              -413 red label with OEM M3 software (friend is a pro tuner)
                              -Unplugged VANOS solenoid, couldn't tell for sure
                              -only 91 fuel
                              -Color of plugs and O2 looks good
                              -new fuel filter
                              -poor gas mileage
                              -threw a "mixture out of range" code briefly a while back
                              -new Bosch knock sensors

                              Don't know where to go next without throwing money at it. Need your help guys!
                              Last edited by M3PO; 05-04-2015, 04:11 PM.

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