Help.... The rev counter has shown no signs of life since I got the car a few months back. I've checked continuity of the wire that goes from the Digiplex (terminal 10) and it's fine. I've also swapped the Digiplexs from top to bottom and with the help of this forum, replaced the SAK215 chip, cleaned and lubricated the innards of the rev counter. As of this morning I also fitted a tested pre owned rev counter - still nothing. I'm getting 12v (rising to 13 when the engine is running) on the green/white wire on the back of the rev counter, using the black wire as ground. The feed from the Digiplex - brown/black wire reads 0.13 - 0.15V, this doesn't change with engine speed, but I'm not sure it would as I believe that the ECU sends pulses as opposed to increasing the voltage. The car starts and runs fine (albeit on axle stands), so I'm at a loss to think what can be causing the problem. Anyone have a clue where I can go next with this? The digiplex units aren't really known for the rev counter output failing, and for 2 to fail on the same car, while giving the same output voltage seems very unlikely. The speedo is also not working (and I think the odometer as well). Again, good voltage on the rear terminals and the wiring seems to be fine. From previous posts I suspected the speed sensor on the gearbox was at fault, so I new one was fitted today, but still no life. The clock has power, as does the odometer. I'm now stumped with this one as well...
I did, and it didn't throw up anything out of the ordinary. To double check I'm attaching a length of wire from the negative on the back of the rev counter directly to the battery, just so I can rule it out. The dashboard lights all work as normal, as do the guages. I managed to get hold of 3 SEN8D crank sensors for £40 delivered, so I'm swapping them all out next week, as I've read that one of them is used to supply the data for the rev counter via the ECU. Also, since posting, I've been at the dash with the multimeter again. Weirdly the odometer circuit board is getting a 12v supply - both permanent for the clock and switched for the speedo, but the output (green wire) that supplies the speed sensor is only putting 7.5v out. I would thought this should be 12v?
Going out on a limb here, but I think that some multimeters will read the pulses as varying voltage because they see more pulses as more voltage over time, being unable to react quickly enough to "see" individual pulses. I suspect you might be able to see this with an oscilloscope, but hopefully someone that really knows will speak up. Because neither the tach nor the speedo work makes me think it is something common to them, though. The ground suggestion is a good one. It does appear that the lights and instruments share the ground, so if the lights work, the mystery deepens...
If your engine runs and you have throttle response, your sensors are alright. One is supplying rpm data to both ecus, the other two are dedicated TDC sensors to each of the ecus.
I don't know for sure... It could be that the speedo sensor runs at the a stabilised, reduced voltage to protect it against car charging system voltage spikes. With the green supplying voltage, the red black should display a voltage variation of about 5V when you turn both rear wheels in the same direction, depending on the wheel position. Here two reference points for testing - green supplies 10.9V in my car: Image Unavailable, Please Login Here the resistance of 4.3 Ohm between green/white and green at the odo: Image Unavailable, Please Login
Thanks for this - it's really helpful My plan of attack is to hook up a temporary 12v supply to the speed sensor on the gearbox, by unplugging the supply side of the connector, and running a fused supply from the battery and seeing what voltage I get on the red / black when the rear wheels spin. If I recall correctly I was getting less than 1v when I checked. I'm beginning to suspect something on the odometer PCB has gone bad. Thankfully my neighbour is a bit of an electronics whizz, as I don't fancy shelling out for a new odometer £££
Thanks Afterburner, I've got that as a saved page on my laptop after spending a few hours trying to avoid shelling out £350 for a new sensor!!! I can't see anything on the schematics that would kill it with 12v - but I'll get my neighbour to take a look for me first. The reason I'm confident that 12v will be fine, is that there's a few threads on the forum about the speed sensor with one of the checks being that 12v is present on the feed side of the sensor on the gearbox.
So.... Rev Counter: All 3 crank sensors replaced, the old ones were dirty but all had a resistance of around 680Ohm so were fine. No surprise that the rev counter still failed to work, the car starts and idles great (as it did before). I then cleaned the earthing point next to the Digiplex boxes and ensured the multiplugs were fully seated for the 50th time, but no improvement. Finally I ran a wire directly from the battery negative to the above earthing point, and to the negative post on the rear of the rev counter, still nothing. The wire from the ECU to the rev counter has been tested for continuity and is good. I cannot think of anything else other than a faulty ECU - but it seems unlikely both would have the same uncommon fault, or 2 duff rev counters - the first in the car when I bought it, the second sold to me as used, but tested and working. Speedo: Didn't get chance to run 12v directly to the sender - the missus gave me 'the look' when I mentioned heading back into the garage.... The schematics on the data sheet mention a 12v supply. My guess is that the speed sensor requires a stable supply hence it's routed through the PCB, rather than just a straight switched supply, which may be susceptible to variation and spikes.. I've had a look at the PCB and looks like one of the capacitors has been swapped in the past and the rheostat for dimming the lights is completely missing 12.2v on the green / white switched - good 8.6v on the light blue / red permanent supply - Bad 7.4v on the green, which slowly falls to 0v after the ignition is cut. I'm getting around 15,000 Ohm between the green and green/white. Looking at the above I'm wondering if a capacitor has gone bad. I also can't figure out why I'm only getting 8.6v on the permanent supply either - I can only think it's my error with the probe somehow, as the same circuit powers the door lights and they are all working fine, as is the clock. I'll revisit it tomorrow... Image Unavailable, Please Login
To have instrument illumination without the dimmer president, you must have a connection between the pink and yellow somewhere. Can you find it?
Can you switch out the tach with someone for a test? Puzzling that it shows no live. Have you spayed contact cleaner and moved the pot inside it left and right?
So now I'm really confused. Went back square 1 with the tacho. Swapped Digiplex units back, checked all wiring and still nothing. Then ran a wire from terminal 10 on the lower Digiplex directly to the tacho (removing the black/brown wire on the tacho first) and it worked! Tried it again shoving the wire into the back of the connector against the black/brown wire on the top Digiplex and it worked again. Removed the jumper wire connected everything up and nothing. That suggests there's a continuity issue with the feed wire from the Digiplex to the tacho, but I've checked it again and I'm getting 0 resistance. Thinking that there's some interference somewhere I've tried tracing the wire from the tacho to the Digiplex. I've unplugged all the connector blocks in the passenger footwell (rhd) and had a look for anything untoward. What I have found is that when I attach one end of my multimeter to the brown/black wire at the tacho (disconnected from it) I'm getting readings from several pins on one of the connector blocks. Surly this cannot be right?
Do you know where the wire from the Digiplex goes? I've got half the dashboard out looking for the elusive brown/black wire, but I can't find it anywhere... I dont want to run a wire all the way to the back if I don't have to. Also, using a jumper wire on the odometer PCB, I connected the green/white and green wires and the speedo worked! The green was only supplying 1.5v, so something is definately dying on that PCB. I'm sure I can find a stabalised 12v power supply and snip off the green wire from the PCB. I think the new capacitor is the 220 one, and for the lights, I can't find anything linking the pink/yellow wire, but there a few extra bits of solder on the PCB
The tach wire is connected behind the left side of the dashboard on the inner multi-plug at the firewall on the rh inner position: Image Unavailable, Please Login
Great photo - helps a lot! Odd question, but you say it connects on the left hand side of the dash - is that for a LHD (mine's a RHD)? I've had a look with my cheap endoscope and followed the connector to the right hand side, where I can see it just like the photo. The problem is that I can't get at it and don't want to remove the dash! I'm assuming it all joins up into one large loom and some of the wires head down to the back of the car.
Mine is a RHD, but the wiring loom plug locations are to my knowledge identical to all cars. Undo the lower dash bolt and you should be able to access the plugs. Those two plugs connect to the loom traveling to the back of the car behind the carpet of the left side sill then up behind the quarter panel trim and through the fire wall. Image Unavailable, Please Login Image Unavailable, Please Login
Afterburner - That's brilliant and helps no end. I wanted to trace the wire as far as possible to see if it's damaged or if a previous owner has spliced something to it. I still can't figure out why I'm getting good continuity with a meter, but the tacho is having none of it.
Did you try cleaning the potentiometer as Afterburner suggested? This usually fixes problems with the tach not reading or reading lower than actual RPM. Alden
One of the first things I tried. The tacho was faulty, as I hooked the original one up to see if i could return the replacement when I found it seemed to be a wiring problem
