Outer Limits 4x4 Board

Hi all,
I'm desperate for any more ideas. I've posted at the Patrol 4x4 forums and had 1 response which was great but didn't help.

Problem: Tacho is dead, unresponsive.

It stopped right after I had a set of glow plugs put in and they replaced a bulb in the dash when i first bought the car (2 years ago, been without tacho for ages). The day after when i noticed it stopped, i took it back. They pulled the dash out and fiddled around, replaced some more globes and couldn't get it to work again. Great.

I've had my own mechanic look at it twice, can't figure it out.

I've been testing it all weekend now and i'm stumped. The tacho wire has 3V or less at the ECU, but has 12V or less at the back of the plug which plugs into the dash.

The needle appears to be fine. It's doesn't stick as far as i can see. I've pulled the tacho gauge out and checked it over. Not much to see there really, all appears fine, no broken solders. Plug is fine, not broken or anything else.

When the engine is running, I've wound the needle around with my finger. It physically feels like it has some resistance up to about 4100rpm then flicks back to 0. Over 4100rpm it flicks down to the redline. Not sure if that's right but it feels fine.

The only thing i can think of it the little silver motor/coil thing in the gauge is stuffed.. but jesus, what are the odds?

Hoping someone here has a few more things i can test and check out before i go buying possibly un-needed parts.

Cheers!

Not sure if the GU is the same as the GQ. I drowned my GQ, and it took out the glowplug controller, which also controls the Tacho. I had to replace the computer to get the glow plugs working, which had burnt out as well, and then the tacho worked again.

Yep, tacho is controlled by ECU unit.

You can check the input from the sensor by disconnecting the plug fron the sensor near the injector pump. Place a multimeter across the two pins that come from the sensor behind the injector pump timing gear. Put it on AC and you should see about 2 - 2.5V peak to peak. If your meter has frequency function you can see the pulses increase with engine rpm. You should see 6 pulses per injector pump revolution.

That being ok, you can then look at the ECU, Tacho or wiring in between.

If you remove the tacho, a gauge place can check it out for you easily and wont cost much.

It sounds like your ECU just needed replacing to get the tacho to work?

AFAIK the GU and GQ are different in as far as tachos and senders etc.. but i will check out the glow plug controller or equivelent.

Cheers m8.