Tach is reading zero
Thread Starter
Heel & Toe
Joined: Jun 2008
Posts: 16
Likes: 0
From: Arlington WA
Tach is reading zero
We have rebuilt a 1976, 350 auto, all new wiring and distributor. We have not driven it yet, still trying to sort all the kinks out in the shop first. When it idles we are not getting a tach reading. It just stays on zero. We have brand new wiring and distributor. Any suggestions?
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
If you're sure you don't have a cable drive tach, then I would start with the fuses.
After that, I would suspect a ground for the tach circuit, and after that I would suspect the circuit itself.
After that, I would suspect a ground for the tach circuit, and after that I would suspect the circuit itself.
Racer
Joined: Apr 2007
Posts: 443
Likes: 0
From: Rexton New Brunswick
Does anyone know an easy way?
Thread Starter
Heel & Toe
Joined: Jun 2008
Posts: 16
Likes: 0
From: Arlington WA
No nothing moves when it's running or when we increase the trottle. I do notice that when I turn the key just so the power comes on and not the car, the tach goes up to the 5 rpm mark.
Drifting
Joined: Nov 2003
Posts: 1,634
Likes: 4
From: Northern NJ
St. Jude Donor '04 & '05
The radio noise filter that's located on the back of the intake manifold. here's a pic w/the filter circled. Try bypassing it and see if that helps.
As far as the tach itself, It is not unusual for the factory tach boards to go bad. There are a couple components that commonly go bad. However sometimes the chip on the board goes bad too, and that chip is now an obsolete part and no longer available. Replacement boards sometimes work, but often don't read correctly.
Are there any darkened/burnt spots on the printed circuit board itself? If so the board is probably repairable. The pic below shows a fellow forum members tach board before it was repaired.
It looks like a goner but ones that look like this are typically the ones that can be repaired.
If you want more info on possibly repairing it, please feel free to PM me.
Good Luck!
As far as the tach itself, It is not unusual for the factory tach boards to go bad. There are a couple components that commonly go bad. However sometimes the chip on the board goes bad too, and that chip is now an obsolete part and no longer available. Replacement boards sometimes work, but often don't read correctly.
Are there any darkened/burnt spots on the printed circuit board itself? If so the board is probably repairable. The pic below shows a fellow forum members tach board before it was repaired.
It looks like a goner but ones that look like this are typically the ones that can be repaired.
If you want more info on possibly repairing it, please feel free to PM me.
Good Luck!
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Drifting
Joined: Nov 2003
Posts: 1,634
Likes: 4
From: Northern NJ
St. Jude Donor '04 & '05
Team Owner
Joined: Apr 2001
Posts: 54,204
Likes: 180
From: S.W. Ohio. . . . . . NRA Life Member
they are electronic starting 1975.
If you suspect the noise filter.... you can temporarily bypass it as a test.
If you suspect the noise filter.... you can temporarily bypass it as a test.
Last edited by Mike Mercury; Jul 8, 2008 at 12:23 PM.
