Rev counter output RB26dett HELP!

[Dayna]

ok, I've got a RB26 transplanted in my cefiro, its been in there for a while now.

I run aftermarket Autometer guages, tacho, speedo, etc etc

The Tacho output off the computer is not working and has been tried on 4 different computers, including the Power FC which i am now running.

I have been using one of the Crank angle sensor wires in the mean time, but i have problems with the rev counter dropping after it reaches 6500rpm back down to 5500rpm then goes back up. It is rather anoying and finally i've had enough.

Now I have tested the tacho wire in EVERY single wire connection of the computer. Just to make sure i've exhausted posibilities, thats how i found the crank angle wire to kind of work.

The engine runs perfectly fine, so every wire that is needed for motor to run fine is connected. Any other wire off the computer is not connected. ]

My question is: Is there another wire that makes the tacho output wire work.

I have taken my tacho into another store that calibrates and alters tachos/speedos etc, and they reckon the tacho works perfectly and should read the 5 volt signal that the computer gives.

I believe a wiring connection is at fault and the computer is not outputting a signal. Would anyone know of anything that may help my cause!!

Cheers

Dayna

[blind_elk]

From memory, pin 7 on the ECU is the tacho signal.

[Dayna]

I know what the tacho output wire is, and have also tested EVERY other connection on the computer.

I am a professionall installer of wiring in vehicles. I do not know the full system diagram of the computer. would anyone have it?

D

[PlasticStan]

I have taken my tacho into another store that calibrates and alters tachos/speedos etc, and they reckon the tacho works perfectly and should read the 5 volt signal that the computer gives.

The ECU doesn't output a 5V signal on pin 7, it's an open collector output that is grounded to generate the rpm signal.

Cheers.

Simon.

[Sumo]

I would be more inclined to pull a negative pulse from the ignition. How the older vehicles used to do it by pulling a varying voltage from 1 phase of the altenator.

I've never taken much notice where the factory tacho on my rb25 has been picked up from... Plus not having diagrams sucks.

Cheers

Sumo