*** tacho still doesnt work!!!!

I've gotten out a multimeter and sussed out all I can without taking the dash out. I also have a spare loom so I decided to tear it apart and trace where each wire goes.

I started at the ECU plug, Pin 101 (it's a 3 plug ECU, being a 90-93 6G72 so I've been lead to believe). This wire splits into three, one goes to the tacho send signal from the PTU, one goes to the instrument cluster, well it goes to a plug that THEN goes to the cluster, and the other I'm not sure of, by looking at hte wiring diagrams it goes to the transmission control unit?

Now my car is manual, the loom I had grafted into my stock loom (my car was 5 speed manual stock) was an auto loom and the ECU is obviously from an auto. Would this be causing the problem? Is there some way it could be thinking it's an auto thats just in neutral so it starts? But there's no signal from the auto so it's not registering an RPM, as I'd assume it'd need the RPM signal to change gears?

I also can't find this plug in my car, nor can I find where he's run that wire, if he's run one at all.

If he's not run one..could that also be the problem...will I need to wire it into something?

Anyway, I have checked for continuity between the wire to pin 101 and the instrument cluster connection on my dash. In my Mitsu service manual it says that pin 45 is the one for the rpm signal to the tacho. This is wired up correctly when I checked continuity. It also says that 46 is earth and the power comes from pin 40.

I've scanned the diagram so you can see what I mean. The scan is the rear view of the cluster, so the connections in the dash will be mirrored:

http://home.swiftdsl.com.au/~monstr/clusterdiagram.jpg

All those connections check out fine.

I checked for continuity between the tacho send wire from the PTU and the wire into pin 101 and thats checked out, I also checked between the pin 101 wire and the plug that goes to the dash just to make sure (and between the plug and the pin 46 in the dash) they all checked out fine.

I just don't understand why it wont work...It's all connected up right (so I believe) the only thing I can think of is this a/t wire needs something done to it.

The guy put a fuse in my fusebox for the A/T transmission too..so I removed that..no difference.

Is there something on the ECU that I need to wire out to make it realise it's manual?

Thanks heaps, this is driving me insane. I'll post some more wiring diagrams of the auto and manual clusters in my magna if it'll help.

Again thanks to anyone who can help me out, Im on my last tether, if I cant get it now..I never will.

Oh and I think this auto problem might be the cause of my check engine light coming on too...


This is a post I made on www.3si.org/forum/ but the retards there won't answer me. Was hoping maybe someone here might have an idea

I can't remember if you have said you have changed it before, but is the tacho unit/drive mechanism ok, if all outputs and signals are ok then thats all i can think of at the moment

Yep all outputs are fine, I checked al them with the multimeter

Then it could be the tacho itself

Not that either, I put it in my old man's KR (the blue one you've seen) and it worked fine.

Just been talkign to another mate, he put a resistor in between the input signal and the ground and that made it work. He said the input voltage was too high.

So Im gunna give it a go

Cool, if you need to borrow any parts from a manual my TS is not doing anything at the moment

Cheers man..much appreciated :D

I may have some time later to help you out.


So when you say you have checked the outputs from the dash wiring loom with a multimeter, does that mean you were in fact receiving a tacho signal? What I mean is for example using a digital multimeter set to 'current' and with the engine running, you should be getting the tacho reading on the multimeter itself. Or have you so far been checking just for continuity?


I don't think the wire that is supposed to go into the A/T box matters, but I'll have to grab the wiring diagram out and check it for myself. Hmm, do you have the wiring diagram for your engine loom?

This is first gen 4 cylinder, so it may not be valid.

What voltage is the pulses that the tacho's getting? If it's usually splitting the voltage to the (non-existant) automatic transmission computer, it could be too high, as was suggested. Try a dropping resistor, and see what that does.

Tried a resistor pot between the tacho signal and earth on the back of the tacho...made SFA difference.

Also I've checked voltage and continuity. It all works as it should...there's just something not right.

Can you scan in the wiring diagram for the ECU from your original TR non-DOHC?

Even better if you happen to also have the wiring diagram for the ECU for the new ECU that works with the DOHC.

I have a suspicion that the wiring for your non-DOHC ECU is closely related to the 4cyl ECU's, and if that is the case, then I can see why you have a problem.

Will do when I get the chance, thanks!