Tacho not working

[Error404]

My tacho has given up, where does it take its signal from? anything I can check?

[Error404]

Forgot to mention, this seems to have manifested itself since I removed the drivers side dash cover to install an electric seat loom, don't think I disturbed anything, but seems likely - what could I have done down there to cause the tacho to fail?

[driftin jo]

IIRC, its pin 40 from ecu, purple wire, check this.

[driftin jo]

After a search it would seem it may be a different colour by the time it gets to the back of the tacho connector, green/ blue is implied at tacho connector .

[Error404]

Cheers mate, I've checked the back of the cluster, all seems well. I wonder if the signal wire goes through a connector at the aux relay panel and I have somehow disturbed it...

[newsh]

It does, there are a couple of smaller connectors, maybe yellow and black?, you can recognise the wire colours and sizes from the back of the cluster.

[Error404]

cool, thanks mate, I'll take a look when i get back off holiday

[Error404]

OK, I've got continuity between the 26 pin yellow dash connector and the ECU, via the oil pressure warning relay and T10 connector by the aux relay panel. So the ECU is either not outputting a rev signal or its not getting one. Is it the grey crank sensor what the ECU uses for engine speed?

Cheers
Alex

[Error404]

This is doing my head in now! Spent all afternoon chasing this fault.
I've tried 3 different engine speed sensors, no joy. Also tried a different set of clocks too.
Could this be a earthing issue? I've checked the 2 earth studs in the drivers footwell, have I missed something?

[driftin jo]

I don't think it would be the ECU not getting a signal as this would through a code.
I could be your clocks have gone **** up, one of my old Audis did this some years ago and I had to change the clocks to fix it.
Is there anyone who could lend you some clocks to try ?

[Error404]

I've tried my spare set already, no joy unfortunately.
Its odd, there is continuity between the ECU plug and the instrument cluster. That's what is making me now think it might be an earth issue maybe?
I am also getting an oil pressure warning with the ignition on and with the engine running, I am sure this is related as the oil pressure warning relay takes an RPM signal from the ECU (blue/green)

Cheers
Alex

[stocious]

is there anything from that circut passing through the fuse box under bonnet? im no sparky by any means so i dont know, but had a coupe with a fecked f/box from water. its funny to watch how much a wet bonnet can "pour" on to the lid of the f/box. other than that good look with it. my temp and mph take turns of working. like shiftwork

[Error404]

I could really do with some advise from the electrical gurus as this is driving me mad now
I have double, triple and quadruple checked all of the connectors in the aux relay panel that I might have disturbed.

I've been chasing this problem now for weeks and spent hours poring over the current flow diagrams and to be frank I'm really confused as to what I should be looking for. I can't find any early 1990 wiring schematics which have the autocheck on them, so struggling to trace wiring properly. Using these Paul put together on S2Centrol and to be fair everything I've checked so far is the same as my early 1990 car. The only Autocheck schematics though are from a 1993 ABY

From what I can see the rev counter only has 3 external connections at the cluster, the engine speed signal and 2 grounds. I have continuity between T26/22 and the ECU which is the engine speed signal, and from T26/23 and T26/8 and the chassis (earth) - all good.
So by default, I'm guessing I'm not getting an engined speed signal which is meaning the rev counter doesn't work, and the autocheck trips the oil pressure warning as it does not have a engine speed signal to compare against?

My car has autocheck, so does that mean my car will not use the J114 oil pressure warning control unit? From what I have read, the autocheck does all the control itself and this J114 is not used on Autocheck equipped cars?
Odd because I have an empty relay holder with all the right wiring going into it according to the J114 schematic, but I don't remember removing any relays

I have also checked continuity between G28 the engine speed sensor and the ECU pins 1c, 2c & 3c - all good.

How can I test the ECU is outputting the right signal?
How can I test the output of the engine speed sensor G28?

Any help appreciated

Cheers
Alex

[mcandmar]

First thing i would do is start the engine then disconnect the speed sensor to see what happens, if it changes or dies you know its doing something as far as the ECU. Ideally you would need a scope to see the signal but you may be able to do a crude test with a multimeter and passing something metallic in front of it. Its really no different to an ABS sensor.

I remember Paul looked at the vehicle speed sensor with a scope and found the raw analog signal going into the ECU gets converted to a nice clean square wave signal, which is also output to drive the speedo. Its possible the same thing may be going on for the RPM signal, but with a fault inside the ECU preventing it from generating the signal.

It is also possible the engine speed sensor may have nothing to do with it, you only need one pulse per crank rotation to drive a rev counter so the crank angle position or hal sensor could be driving it instead. Put it this way in ye olden days of points and distributors they were driven off the coil.

I think you can forget about the autocheck as its self sufficient, my CQ never had it originally and all i did was plug it in. The oil pressure warning light/beep has only ever come on from me when i cranked the engine it fired and cut, for example if you start it without the fuel pump running. My take on that is the control unit only activates when it sees an engine speed signal, other wise it would go off every time you turn the ignition on. Is it working as normal or playing up too?

[johne]

So by default, I'm guessing I'm not getting an engined speed signal which is meaning the rev counter doesn't work, and the autocheck trips the oil pressure warning as it does not have a engine speed signal to compare against?



My car has autocheck, so does that mean my car will not use the J114 oil pressure warning control unit? From what I have read, the autocheck does all the control itself and this J114 is not used on Autocheck equipped cars?



I have also checked continuity between G28 the engine speed sensor and the ECU pins 1c, 2c & 3c - all good.

How can I test the ECU is outputting the right signal?

If you can get access to an osciloscope or an osciloscope interface to a laptop you can look at the output signal from the ECU.

How can I test the output of the engine speed sensor G28?

If your car is starting and running fine, I believe G28 must be working fine. G28 is only a coil of wire so very unlikely to fail.

Given the problems I've had recently with random broken PCB tracks in my instrument cluster, the fact you've got continuity to T26 doesn't g'tee things are going to work or that there's continuity up to the tacho.

Can you try and borrow another instrument cluster and plug that in?

I'll have a look over the wiring diagrams and see if I can suggest anything more helpful.

I assume you've got a 3b and everything other than the rev counter and the oil pressure autocheck alarm work fine?

John