Intermittent tach issue in my 92 SC

[Kurt K]

I've had an issue for several years that the tach will drop to zero and a check engine light will appear when I'm driving. It never happens when the outside temperature is below 45-50 degrees....even in the summer, everything will be fine until I get to the 1st extended stop light. So I know the issue is heat related. When the tach drops to zero, the car still runs fine. I've changes the cam and crank sensors and I still get the intermittent issue.

I assume it is something to do with old wiring under the hood, but I'm not sure where to start. Or is it possible that the tach itself is the problem?

 

[MadMikeyL]

I would suspect the DIS module. If you have a spare OEM one, I would swap that out and see if the problem goes away.

 

[Kurt K]

I would suspect the DIS module. If you have a spare OEM one, I would swap that out and see if the problem goes away.

Actually, I replaced that too, but forgot to mention it.