OK Fellers,
85' GT, 2.8, Auto

Tach hasn't worked since I took ownership. (Needle doesn't move, jump, or look at me longingly. It does nothing. Kinda like an elected official now that I think of it.)

This project is moving up my priority list so I figured I'd start a thread and gather what info I could from the experts.

So considering I'm not a mechanic by trade, my technical / mechanical level may be considered average. I know enough to be dangerous.

Troubleshooting -
Do I start at the distributor / tach filter?
Or the opposite end at the tach itself?
I read that a common occurrence is oxidation causing issues at the filter. I'm guessing that's the easiest place to start. BUT - if there's no corrosion / continuity issue, is there a meter reading to look for? Idle, rev, etc?

Detailed responses greatly appreciated.

Thanks in advance guys.

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Bakeys
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[i]'85 Fiasco GT[/]

Only 2 reasons why it's not working.

1. not getting signal
2. it's dead

Check the wiring at the tach filter.
You can also bypass the tach filter and see it that makes any difference.

The tach may not be getting a good connection in the cluster.
Pull it out and put it back in a couple of times so the contacts rub.




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My World of Wheels Winners (Click on links below)

3.4L Supercharged 87 GT and Super Duty 4 Indy #163

[This message has been edited by fierosound (edited 08-28-2016).]

The tach, if it is getting power, should put the pointer on the zero mark when the key is turned on. So if the tach pointer is not on zero and doesn't move key on, look at replacing the tach. If the tach just stays on zero all the time then this won't help you.

Fyi - buying a used tach - many (most?) tach boards have gone out of accuracy over the years. When looking for a used tach look for the seller to verify its accuracy if possible. Also 4 cylinder and 6 cylinder tachs are different, some tachs have the oil pressure gauge as part of them and some tachs are back lit while others are not. So consider all of those when purchasing.

Also if needed - I can calibrate an off tach or alter a 4 cyl tach into a 6 or 8.

[This message has been edited by phonedawgz (edited 08-28-2016).]

Maybe you can be an early tester for the new tach circuit board..
New board is crystal accurate, and you can add a button to show tach memory (highest RMP for 1/4 mile runs, etc).
https://www.fiero.nl/forum/Forum2/HTML/138292.html
I have the software partly done, and a new board will be ordered to take on the GT.. so not quite ready, but if you can work with me, I can be ready for you to test in say 4 weeks.
Wanna be a guinea pig?
(Edit) assuming that you have a signal at the dash from the ingition..

[This message has been edited by Chris Eddy (edited 08-28-2016).]

OK, it's been a busy Sunday for me. Pardon the slight delay in responding.

quote "...connect the mating coil from the J-33431 tester to the connector just removed."

OK, now if only I had me a J-33431 tester.
But I see there's some power involved so I think I can wing it with a multimeter.

quote The tach, if it is getting power, should put the pointer on the zero mark when the key is turned on. So if the tach pointer is not on zero and doesn't move key on, look at replacing the tach. If the tach just stays on zero all the time then this won't help you.

Then this won't help me. Needle is stationary. NO movement whatsoever.

quote Wanna be a guinea pig? (Edit) assuming that you have a signal at the dash from the ingition..

Ummmm, I dunno.
Let me do some troubleshooting first and see what I come up with.

Thanks all for the replies. Could be a few days before I get under the hood again. But I'll try to keep y'all posted.

I suggest a test of the tach meter itself, which if you have an ohmmeter, is easy..
Take the movement out of the instrument panel.
There is a PC board on the back of the tach, remove the hex nuts on the posts and remove it.
On the tach movement, there is a common post and two coil connections. The common is not the center post, it is one of the other two.
You should read somewhere between 200 and 240 ohms from common to each coil, or 400-480 ohms across both coils.
If one of those two coils is open circuit, the needle will not move.

Good advice Chris!
I'll give that a go if I get a signal from the tach filter.
May take a while before I get to it though.

Thanks!