I've got a 1992 F-350 7.5L that I just took out of storage. Putting it away tachometer worked great a few months ago, and now tach shows 2500 while idling and doesn't level out at all after a little bit of time.

Are your thoughts distributor pickup sensor, crankshaft sensor, or something else?

thanks in advance

 

Or a bad oem tach?

 

I would say a bad tach. My '88 did that and I replaced the dash for another reason and now my tach registers as it should. Will your tach go above 2500 if you speed the engine up?

 

It fluctuates. Sometimes zero, 2500, 5000, and anywhere in between.

What provides tach its signal?

 

The pip inside the distributor supplies the tach signal, if it was no good, then you'd have running issues in addition to the wacky tach readings....as the pip also supplies the signal to the eec in order to determine fuel and spark timing.

 

You could try removing the tachometer module and resoldering the connections. I have done this on several of my trucks. fixed my tachometer problem every time.

 

I’m having very similar issue, mine sticks around 2500 but seems to function just at the incorrect readings. When I rev the truck it’s moves accordingly it’s just giving incorrect values. Any help would be greatly appreciated