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No tach or MPG gauge, but OBC MPG works...

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    #1

    No tach or MPG gauge, but OBC MPG works...

    This morning I went out to my car, and the tach and MPG gauge both were not working. I tried tapping the cluster a few times (hey, works for the temp gauge!), then traced the wires from x20/c101 (It's an m50 swap), back into the c103 (it's an 85 325e with the 3 wire connector at the glovebox). All connections seemed good. I didn't have my multimeter on me to check for voltage, nor am I sure what kind of signal/voltage to check for.

    The OBC is still accurately calculating MPG, and I know that is somehow tied into the system. According to the schematic, the fuel rate output signal goes into the cluster, then out to the OBC. So if the OBC still works, the signal to the cluster has to be good. Did the gauge just fail? I am going to try swapping in a spare cluster, and if that works, I'll try swapping just a new tach into this cluster. If anyone has any other ideas in the mean time that don't involve just throwing more parts at it, let me know.

    Here's the tach schematic:


    85 325e m60b44 6 speed / 89 535i
    e30 restoration and V8 swap
    24 Hours of Lemons e30 build
    Tags: None
    #2
    A bad SI board can cause those symptoms.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

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      #3
      Pulled the cluster apart. It had the replacement SI board with lithium batteries, everything looked great. Measured 3.1 volts across each battery.

      Swapped in another lithium SI board from a spare cluster that measured 2.8 volts across each battery, now everything works fine.

      Weird.
      85 325e m60b44 6 speed / 89 535i
      e30 restoration and V8 swap
      24 Hours of Lemons e30 build

      Comment

        #4
        It appears that the SI board had a failed component. Usually when I see that it is on a board where the batteries have leaked.
        The car makes it possible, but the driver makes it happen.
        Jim Levie, Huntsville, AL

        Comment

          #5
          Originally posted by jlevie View Post
          It appears that the SI board had a failed component. Usually when I see that it is on a board where the batteries have leaked.
          Yeah, either that or maybe a bad connection that was temporarily fixed when I took disassembled and reassembled the cluster. The board had no signs of corrosion. I didn't test each individual component or anything, but I didn't see anything out of the ordinary like a blown capacitor or melted resistor.
          85 325e m60b44 6 speed / 89 535i
          e30 restoration and V8 swap
          24 Hours of Lemons e30 build

          Comment

            #6
            Sort of off topic.

            Car: 87 325ic with 89+ engine/ecu harness and Miller W.A.R. chip.

            All's well, but, tachometer does not work.
            did s.i. batts, swapped in a cluster w/ working tach and nothing.

            So, stuck at matching small ecu connectors to small cluster connectors near obc side, colors and plugs are not same., it would really help if some one would post...

            a) A pic of cluster's small single connectors attached to green port
            b) A pic of pre 89 325i ecu harness smaller connectors.

            or prehaps is the w.a.r. thing interfering?., I screwd-uo, but where? I'm waffleswaffleswaffleswafflesfused

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