Rev counter not working..

[Shmallpaul]

Hi Guys,

Just bought a very nice e30 325i.. fantastic car with various issues as you might expect, just one I can't figure out

Rev counter doesn't work. Temp gauge is also intermittent, i've tried the fuse (10?) and no good. I also have an entire spare set of clocks which I have tried fitting today and still same issue, everything works except the rev counter which never works and the temp gauge which does when it feels like it.

I have tried checking the cables from the connector to as far as I can follow it, and all looks fine.

Any ideas? I'm thinking either a cable is broken somewhere (any idea on typical places etc this might have failed at?) Or maybe that both my clocks have dying batteries giving the same fault? (unlikely I know..)

Any input is much appreciated!

[b12rlw]

Service indicator (.SI) board batteries???

[Shmallpaul]

Possibly, but with an entire seperate set of clocks, showing the same fault?

As the batteries are contained in the clocks its showing the same fault with a different set of batteries

[Shmallpaul]

Have put some new SI batteries in and rev counter still doesn't work.. driving me mad! any ideas people?

[b12rlw]

Have you traced the cables and confirmed their condition?

[G-Bear]

For the rev counter. Check the wire running from the diff. It usually goes somewhere within 30cm from where it plugs in. I think i've read that the connector is the same as what plugs into the head lights, so you could get a new length and plug from another e30 at a scrappy if the wire is manky..

[G-Bear]

Sorry ignore my contribution. That's for if the speedometer has failed. Early morning blearyness.

[Grrrmachine]

They can both be affected by the SI batteries, and the temp gauge issue may be the brass nut. But both signals come through the blue plug on the back of the cluster; tacho is pin 7 (black wire) and coolant temp is pin 26 (brown/violet).

Unfortunately tacho is a square wave signal so unless you have a pro-quality multimeter, you can't check it. But you can check for continuity between the dash and pin 6 (black wire) of the ECU. ECU won't work without engine speed, so that should be fine, so it's either a fault of the black wire or you've got two broken gauges.

What you'll probably find is that the black wire has been damaged at the C101 plug on the bulkhead; pin 7. So check the pin/socket for corrosion.

http://www.e30zone.net/e30zonewiki/index.php/C101

[Shmallpaul]

Temp gauge issue is resolved since putting some new SI batteries in, so just the rev counter now.

Thanks for the info on the c101, i will have a good look at this on the weekend

and yes both the rev + mpg gauge don't work, car is facelift, and is a 325 on the logbook, and have changed all the above fuses.

[Shmallpaul]

Update:

Checked the c101, and there is no black wire in pin 9, on either end of this connector. So assuming I have found my problem, black wire runs from the clocks so at some point it must just be missing..?

Any ideas/easier solutions that getting all the wiring apart to run that cable?

[Grrrmachine]

There is no reason for that wire not to exist. Can you confirm the age of the car so that we can check the wiring diagrams?

[Shmallpaul]

Its a 1987 E reg, I can't tell you exact month as its a recent buy and logbook hasn't arrived yet (did check before buying that it was a 325 though!) It has the motronic circular connector as shown http://www.e30zone.net/e30zonewiki/index.php/C101 here. All the other wires match up as per that diagram.. just no black one in pin 9!

[Grrrmachine]

Right. A 1987 is one of the earliest 325i's, and they did have slightly different wiring. Your tacho signal will be coming through on Pin 14, on a black/white wire.

I really ought to get this info onto the Wiki:



This should still go to pin 6 of the ECU, if you want to check for continuity along the wire.

[Shmallpaul]

Thanks again for the help, however.. there is no wire in pin 14 either! The only black/white wire is in pin 16, as per the above diagram

[Grrrmachine]

No wire at pin 9 I can understand, but are you absolutely sure there's no wire at pin 14? It would be very strange if so.

You're at the point where you're going to have to disassemble something otherwise. If that's the case, you're most likely going to have to remove the dash cluster to check that all the plugs are in there solidly. It's not impossible for one of the plugs to come loose (and therefore lose the tacho) when fitting or removing a stereo, so if the previous owner removed his CD player before selling you the car then this might be the problem.

[Shmallpaul]

and the other end that goes to the fuse box..

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and yeah to be honest as all the wires in the c101 are all in pretty good nick figured that this is not going to be an easy fix!

[Shmallpaul]

I think its 3. but to be honest not 100% im looking in the right place?

[Shmallpaul]

Ah thanks for the picture, yes I was looking in the wrong place, read your last comment wrong (don't ask..)

Yes the ecu plug is 2 rows, and the 3 pin pictured is connected to another 3 pin connector.

Can someone point out to me the complete route of the rev counter cable? I know its present behind the clocks, and hits a T junction and from there I don't know. If I am missing the correct cable at the c101 end, does this mean I will have to route a new one in?

At this point is it perhaps easier to chuck an aftermarket one in and mount it on the dash? its a weekend/potential track car so I'm really not bothered as long as I have a rev counter of some kind!

Also forgive me I am not as mechanical as most of you helpful people are on here, however I refuse to pay someone to fix this haha

[Shmallpaul]

Right ok, so what exactly goes through the c101 in regards to the rev counter?

and as for ecu not sure which number is relevant but 1 289 786.9 / 078 / 0 261 200 073 (this?)

[Grrrmachine]

the last number (073) corresponds with you having the oldest type of 325 engine, and matches the wiring headaches we're encountering. It also means you have the C101 style "baujahre 85 bis 87" - the first round type. If you look at the diagram, there's a white square underneath the C101 plug which outlines the C104 plug that willnz has given you a photo of. Pin 1, Drehzalsignal, is the tacho signal, which runs under the dashboard from the ECU directly to the cluster. It will still be a black wire to pin 7 of the blue plug on the back of the dash.

[Shmallpaul]

Right. So you are saying there must be a fault somewhere along the black wire which runs from the clocks, into the c104? That makes things much easier in that case, as thats not much distance to mess about with

If I try run a new wire to both points, what should I look for when buying a new bit of wire? as i said, not very car technical ;)

Thanks again for the help guys

[Grrrmachine]

what you really need to do is get the clocks out, and do a continuity test between the wire in the C104 and the appropriate pin on the dash blue plug. You'll probably find out the wire is fine, in which case one of the plugs wasn't plugged in properly, or it's a fault with the dash cluster.

[Shmallpaul]

Ok will give that a crack at the weekend. thanks again

[Shmallpaul]

Sorry guys been busy the last few weeks, just tried doing a continuity test between the black wire on the dash cluster and the black wire on the c104, and then from the c104 to the ecu connector and all tested fine..

Any ideas what else this could be? faulty ecu maybe?

[Shmallpaul]

bump, any ideas guys?