need help with rpm gauge

[chudson91]

Ok i have searched and found nothing.

I want my rpm and eco meter gauge to work.

I have switched the si board(nothing). Then i purchased a known good cluster and nothing.

I have checked all the fuses and all are good.

What else am i missing???

[jlevie]

What car is this?

[chudson91]

1989 325i

[jlevie]

Is the engine wiring harness the one the car was built with? If the harness has been replaced with one from an an early (9/86-8/87) M20B25 the harness would not have the wires in it for the tachometer and econometer. If the harness is original and you replaced the SI board with a new or known good part either there is a problem with tachometer & econometer circuits or there is a problem with the DME.

[chudson91]

As far as i no the harness is original. The PO told me ever thing that he had done with it and that was not on the list.

I just dont no where to go or look from here.

[chudson91]

Is the engine wiring harness the one the car was built with? If the harness has been replaced with one from an an early (9/86-8/87) M20B25 the harness would not have the wires in it for the tachometer and econometer. If the harness is original and you replaced the SI board with a new or known good part either there is a problem with tachometer & econometer circuits or there is a problem with the DME.

Is there any way to trace it down?

And if it is the dme can it be fixed?

[jlevie]

The DME can be replaced if it is the problem. You can pull the cluster and check for the tachometer and econometer signals with an oscilloscope.

[chudson91]

The DME can be replaced if it is the problem. You can pull the cluster and check for the tachometer and econometer signals with an oscilloscope.

Ok yesterday i found a tag off of 3 wires going off the dme.

The tag is date 4-11-87 WTF

So i guess the po replace the motor and used the 87 wiring harness.

Now my ? is what can i do to fix this?

[jlevie]

it may be that you have an 87 harness, in which case the easiest fix would be to replace the engine harness with one from an 88 or later. Other wise some rewiring will be required to get signals from the DME to the cluster.

[chudson91]

it may be that you have an 87 harness, in which case the easiest fix would be to replace the engine harness with one from an 88 or later. Other wise some rewiring will be required to get signals from the DME to the cluster.

If thats the case, is there any way to find out which wires to jump. Ive looked and looked trust me. Just cant seem to find the right answer.

[jlevie]

The early harness, up to 8/87, routes the tachometer and econometer signals to the cluster via C104 off the engine harness. Later production routes those through C101. So adapting the early harness to a late is a bit of a mess. It is easier to just change the harness.

[chudson91]

well i check voltage at the blue connector(solid black wire) and i have 3.7v ac. As i hit the gas the voltage increases. Also the black wire coming off the dme is the same voltage.

So im either missing a ground wire or my gauge is messed up. Except this gauge cluster was a known good one.

[chudson91]

Ok I figured it out. I was missing my 12v signal lolol. I checked the fuse 21 and voltage. I assumed it was going to the cluster but was not.

[88e30vert]

How did u solve this problem. I'm having the same issue after I removed my remote starter harness. I don't know how this could be involved but it was a spaghetti factory of wiring under there and maybe I unplugged something by accident.

Thanks

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