Neverending rev counter problem..

[Shmallpaul]

Wondered if anyone could help me figure this one out, had a totally non working rev counter since I bought my pre-facelift 325I.

Things I have tried:

- Replacing SI batteries.
- Replacing entire clocks. (both clocks work fully except for the rev counter)
- Continuity between black wire in instrument cluster to c104 3 pin connecter and to ecu. all fine.
- Replaced whole ecu (not to try and fix this problem new one is chipped but worth mentioning!)
-Check C101 loom for any loose connections etc. all fine.

Any other ideas? Crank position sensor possible for this one? Engine runs sweet as a nut otherwise.

Driving me mad!! Just gonna bolt a tacky aftermarket one on the dash at this rate!!

[milescook]

Fuses? Sorry someone will say and I've learnt my lesson the hard way not to discount them

[jimjim]

I had this problem in a 316i I had. If i remember right look under the passenger side footwell under the carpet and about 3 or 4 big wires join there and they corroded.

[jimjim]

i think they were green and red or yellow and red, cant remember exactly

[Shmallpaul]

Did check all fuses when I first found the problem (10,21?) and were ok. Will check tomorrow again though cos has been a while!

Will also check wires but as all my carpets aren't present pretty sure I have checked every plausible wire around the car and under the dash!!

[Brianmoooore]

You've done everything that is relevant to a working tacho! There are no fuses that affect the rev. counter that don't affect other obvious things in the car, and the rev, counter signal is derived from the same signal that operates the fuel pump and provides sparks, so there can't be any sensor problems.
If you have continuity on the black wire from the ECU to the cluster plug, and have infinite resistance from this wire to earth, then there's nothing left but to retrace your steps.

[Grrrmachine]

If all the main components have been replaced, I'd be checking the loom for micro-splits, possible shorts along the route or loose/cracked pins in each plug. The wire may have continuity when tested with a meter, but if the plugs aren't making proper contact when connected then nothing will work.

[Shmallpaul]

hmm ok cheers guys, will have another crack this weekend see if I can find anything else! Pain in the arse..

[Speedtouch]

I take it you have seen the Zone Wiki guide on this:

http://84.45.115.78/e30zonewiki/index.php/Instruments

"However, on older vehicles (earlier than 1987) the simpler engine management system provided tachometer and fuel rate data through a separate plug, not the main loom. If your pre-facelift car has Tachometer issues, try to locate the small three pin plug and socket above the pedal area, and ensure that it is connected properly."

[Shmallpaul]

Yeah randomly started it up for the weekend, rev counter suddenly decided to come to life! 2 months or so of using the car and never seen even a flicker, played around with cabling under the column until i found a cable that when moved would make it go on and off, a 3 pin connector (not the c104) near the top under the clocks.

Finally have working revs! now only another 300 problems to fix

[Speedtouch]

Congratulations, Paul!

P.S. If you're happy with the ECU, please feel free to leave some feedback on E-bay.

[Shmallpaul]

Ah yes mate will do.. usually forget these things

[Speedtouch]

Many thanks, fella.