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M42 Almost No Start - Input Needed

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    M42 Almost No Start - Input Needed

    This is a rather unusual issue and I need some outside advice. I'm dealing with a 91 318i - I bought this to use as a donor for an early model that I'm putting together. I was aware that the car had a destroyed harmonic balancer when I acquired it. Since then, I have replaced the failed balancer with a used unit. While I expected it to immediately fire off, that was not the case. Instead, I was left with a condition which seems to mimic the timing being off - it will start and run for a second or two, roughly, and then die. Going down the rabbit hole yielded:

    a faulty air flow meter (IAT was shorted, causing the DME to believe the incoming air was 355 deg. F)
    damaged idle control valve wiring, which was repaired
    fuel pressure verified at 45psi
    timing verified (blocks on cams, pin in flywheel, index mark on balancer lines up w/arrow on oil filter housing)
    Two intake leaks were discovered and repaired
    A compression test was performed (obviously cold, 1-142 2-152 3-149 4-145)
    verified wiring to the coils to ensure the correct plug wire orientation.

    When looking at data inputs w/a scan tool, all of the values I am seeing appear to be normal.

    Any ideas? Have I missed something obvious? I'm considering DME failure as a possibility at this point, nothing else seems to add up.

    IMG_0145 by Jonathan Martin, on Flickr

    #2
    I'd look again at the damper, make sure it isn't bent and spinning out of round. Then I'd electrically and visually inspect the crank sensor/spacing from the trigger wheel.

    It's also worth verifying fuel and spark delivery if above checks out.

    Any other known recent work from the PO?

    Comment


      #3
      Spray some carb cleaner into the intake and see if it runs. Sounds like fuel to me. Perhaps the pump is building slowly to 45psi but then can't maintain.
      sigpic

      (clicky on piccy to get to thread)

      Comment


        #4
        Realized I left out a couple of things yesterday - I did ohm out the crank sensor as well, pins 1&2 were 509 ohms, 1&3 + 2&3 were open. I believe this to be correct based off of a post from M42Club. The gap between the sensor and wheel also measured out within specification.

        Recent work done by PO - fuel pump, camshaft position sensor was replaced. He refused to believe the balancer had disintegrated even though I was adamant that it had.... found the split balancer within 5min of taking delivery.

        I'll have to verify spark on every cylinder though I definitely had it on cylinder 1. That may well be my issue.
        IMG_0145 by Jonathan Martin, on Flickr

        Comment


          #5
          How did you get data input on the obd1 car?

          Comment


            #6
            Originally posted by dlmrun2002 View Post
            How did you get data input on the obd1 car?
            There are scanners that interface with the diagnostic port in the engine bay that allow for reading quite a few values.

            Comment


              #7
              Is that a plug adaptor from obd2 to obd1 or a specific scanner?

              Comment


                #8
                Originally posted by dlmrun2002 View Post
                Is that a plug adaptor from obd2 to obd1 or a specific scanner?
                Both, at least in the case of the Schwaben one I have, which is just a Foxwell Tech product that's rebranded. It may be possible to just use an adapter on a standard OBD scanner, but I have not tried it.

                Comment


                  #9
                  is the Crank Position Sensor OE BMW? I've replaced quite a few in the various M42s I've owned, and while the aftermarket ones were ohm'ed in spec, simply replacing it even with a used BMW one fixed similar problems with starting/running
                  1991 318is ---230K - DD
                  1991 318i ---- 308K - retired

                  Originally posted by RickSloan
                  so if you didnt get it like that did you glue fuzzy oil to the entire thing?
                  sigpic

                  Comment


                    #10
                    I have no idea. Ended up putting the car for sale as I decided to go V8 w//the shell it was supposed to donate to. If it doesn't sell, I'll make another attempt at getting it going. I have viewed it as suspect due to the balancer failure, I would not doubt if it proved to be (at least part of) the problem.
                    IMG_0145 by Jonathan Martin, on Flickr

                    Comment


                      #11
                      Seeing as I haven't sold this, it's time to get back on it. I'm very interested to see what turns out to be the actual problem. Recently, I acquired a Snap-on diagnostic cart w/a 4 channel scope, I'm going to pull some data this weekend and see what I get - suspecting a questionable crank sensor due to the balancer failure.
                      IMG_0145 by Jonathan Martin, on Flickr

                      Comment


                        #12
                        Mini-update: I have a DME, wiring harness, and crank sensor in route to me. They should arrive toward the beginning of next week.
                        IMG_0145 by Jonathan Martin, on Flickr

                        Comment


                          #13
                          did you make sure the spark plug wires are going to the correct cylinders? It could run with them swapped but won't run right or for very long

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                            #14
                            We have success! All of the replacement parts arrived and were installed - it immediately fired up. Upon further investigation, there were several problems at play here - the wiring harness had a significant amount of damage leading to the main relay and fuel pump relay, the DME had slight water damage, and the ICV was installed backwards.

                            Seeing as it now runs, I get to take it apart....
                            IMG_0145 by Jonathan Martin, on Flickr

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