93 K2500 /w 6.5 TD engine

The truck appears to be running just fine, but after I hit around 2500 rpm, the tachometer starts "jumping" between 2500 and 4000 rpm's. The engine speed is not changing.

Any thoughts as to what I should start checking first?

Thanks,

- Shawn

Grounds... clean them all. one on each battery, one on each side of lower intake, and braided ground straps near starter.

Also check all connections to the alternator.

If your 93 tach takes its numbers from the alternator sounds like its time for a new belt, check to see if your tensioner is as far as it can go, if so replace the belt.

I had the same thing right before my alternator quit - something to check.

:exactly:
I had the same thing right before my alternator quit - something to check.

Diodes sound suspect in alt. Do the grounds first, do the alt second if need be.

I had the same thing right before my alternator quit - something to check.

This is exactly wha happen to mine for about 6 months before the alternator just quit. I had quit chasing it and given up ever fixin it then like magic new alternator and tach worked gre8t.