erratic rev counter,any1 help?

[jagtech2002]

got an 89 318is with an erattic rev counter! some times it won't work at all yet on other occasions it with shoot right round into the red and i ain't floorin it! can any one help??

[irish320i]

have you replaced the batteries on the back of the cluster these can cause the gauges to get a bit irractic if there gone

[jagtech2002]

No i haven't replaced them, had it stripped earlier and saw the batteries you are talkin about, checked all the pcb's for dry joints, cracks etc but all seemed ok. what is the purpose of the batteries? are they in any way related to the operation of the rev counter? aren't they for the mileage memory or for the service interval indicator?

[Brianmoooore]

Are your batteries 3 volt lithium types or 1.2 volt NiCds?
The lithiums don't tend to give trouble, but the NiCds tend to go short circuit and pull down the supply voltage of the electronics in the cluster. They can also leak and corrode the electronics.
Personally I doubt if your problem is the batteries. Check pin 9 (black wire) of the C101 engine loom plug and socket.

[jagtech2002]

interesting, they are definitely the lithium batteries, i will check pin 9 of the engine harness,where can i trace it back to, in order to check for continuity? or is it just a poor connection i am checking for at the connector?

[Brianmoooore]

Poor connection. Rev counter seems very sensitive to the slightest problem at the C101.

[jagtech2002]

okay cool, I will check it tomorrow, see what i can do with the dreaded pin 9! thanks for your comments will respond t'moz with, what i hope to be some good news!!!