My tach is reading about 1000 rpm high...???

[Chuckcruzin1986]

We went through my M20 (87 engine) and it is running but it seemed to show high on the tach. We hooked up a timing light with built-in tach and there was about a 1000 rpm difference! 4000 on my tach and 3000 on the timing light. I am lost. Ideas would be appriciated.

I just thought of something. The car is a 1986 325es with a fairly "high" diff. But doesn't the engine speed and tack come from the engine sensor at the front pully sprocket? I have the 87 wiring harness and computer installed with this 87 engine.

Chuck

[eta]

Someone may have changed the cluster at some point and you know have a 4 cyl (316i/318i) coding plug behind the rev counter.

[Wh33lhop]

Diff has nothing to do with it

If you have a 4cyl coding plug, then your tach will be reading 50% too high, i.e. 4500RPM when you're really revving 3000. This is probably your issue.