Tach wiring issue

[Streetwise guy]

http://www.300zx-twinturbo.com/cgi-bin/manual.cgi

Not so good a diagram, but what you want to do is trigger from any of the coils, on the wire running to the power transistor unit. There will be two wires at each coil, one of which is powered all the time from the coil relay, the other is the pulsed ground from the power transistor unit. Key on engine off, unplugged coil, one wire will be powered, the other dead. Trigger from the dead one.

The signal from the ecu is probably a digital 5 volt low amp signal. Hooking the tach directly to that would probably just result in a misfire.

Your tach will accept a didtributorless signal, as in one pulse per two engine revolutions, I hope.

[Tristan Smith]

Thanks, Bonespec, Streetwise and Greg.

This is what I suspected, so now I have to do my homework and see what will work. I appreciate your help.

[DavidM]

Don't know if you got it fixed Tristan. A quick search of "tach install" over on twinturbo.net shows people using the wire sited in the installation instructions. There's even a shift light install in the tech section using that wire. Maybe post over there and see if anybody has any ideas.

There is a power transitor unit (PTU) wire like Greg said. There's a little loop of wire that sticks out near the electronics on top of the motor. This is where a lot of people clip inductive pick-ups for timing lights. That's the PTU wire. You could try splicing into it and see what happens.

David

[Tristan Smith]

Hey David,

I put an oscilloscope on the ecu tach output wire the other night. No signal whatsoever. So I think that there is an issue with the ECU. I am going to try to track that down in the next week or so, and see if I can get my hands on another ecu to see if that is the case. It would be nice to get this issue cleared up.

[DavidM]

Weird. I know on the 240 the signal that feeds the tach is the same signal that feeds the coil. The stock tach on my 240 went bye-bye before Barber so I was just looking at the wiring diagrams to put in another one.

I haven't looked at the diagrams for the 300 to see if it's the same deal. I'd think the car wouldn't run if that was the case, though, if you're not seeing anything on that wire.

Good luck.

David

[Tristan Smith]

The ZX has a coil on plug set up with a power transistor unit. It get's trigered by the crank angle sensor. The ecu (I believe) then sends that signal on a seperate wire to the tach (the yellow and red one just like the 240sx). The car runs fine, but so signal at that wire.