Ok, I have a 85 rx7 with a standard 12a that runs great with only one problem. I can drive for approximately 20 minutes and the tach stops working. All four plugs are firing and the car runs perfect with the tach not working. Timing light shows that the trailing is working perfect.

I replaced the all plug wires, the tach, wiring harness, all relays under the hood, both ignitors, both coils and the distrubitor.

After the car sets for a couple hours the tach starts working again. Any suggestions would be appreciated.
Thanks

 

That's funny, I have the OPOSITE problem. My tach won't work for the first 15 minutes or so, and then will work partially. After about 20 minutes it works just fine. Strange.

 

You've done everything I could possibly think of... I can't think of anything that the tach could even be influenced by. That sucks man.

 

Well, I don't know what else to try. I give up. Thanks

 

Hmm.. Maybe you have heat issues. I read a post a while back where someone recommended wrapping all the wires under the hood with heat tape. He was tuning and the wires' resistance was changing on him because of the heat. Just a thought...

Everything else you've changed is the whole system afiak, so something must be influencing an otherwise perfectly functioning system.

 

Thats the only thing that would make sense... heat issues. But that still shouldn't happen. Maybe it's just a coincidence that it works on startup and you have a bad connection or something? You could always swap out the trailing ignitor anyway, even though its working. Sometimes stupid things like that fix the problem. Besides... how much are ignitors? Like 1.50 or something rediculously cheap.

 

I've replaced the ignitors a couple times, but I'll try insulating the wiring.

 

Try it, but that really shouldnt matter. If its because of heat, you have something not right under that hood

 

Sounds like the little voltage regulator for the gauges is going into thermal runaway.

 

Where is it located?

Sounds like the little voltage regulator for the gauges is going into thermal runaway.

 

I believe it's on the back of the instrument cluster PC board on RX7s. It'd look like a little metal box. If you swap out the whole pc board, I'll bet your problem goes away.