Dialed_In

iTrader: (3)

'88 L98/700R4.

I'm having trouble tracking this problem down. With the engine running, the tach bounces between 3000 and 4000 RPM. I just had the engine apart and while I was at it I removed the entire engine harness, stripped all of the tape and loom, inspected and repaired any damage I could find. I thought I would find the problem that was leading to the tach issue but I didn't find anything.

Has anyone had this problem before?

Dialed_In

iTrader: (3)

I should mention it's got a new cap, rotor, plugs and wires and runs fine.

HawkZ28

iTrader: (2)

Bad connection at the coil for the tach signal? Hows the printed circuit board look?

Dialed_In

iTrader: (3)

Connection is tight at the coil and distributor plugs. Haven't pulled the cluster out to look at the circuit board.

RBob

iTrader: (1)

Hit the electronics board here at TGO. Up in the sticky's is a long thread on fixing the tach driver board. A resistor goes bad which is easily replaced.

RBob.

HawkZ28

iTrader: (2)

I had to do the same fix on my tach that RBob is talking about- it was reading way high, but didn't bounce like you're describing. My bad for pointing you in the wrong direction. I didn't realize that was another symptom of the diode going bad.

FWIW, it's a really easy fix. If you've gone through your wiring harness, the fix will be pud for you.

Dialed_In

iTrader: (3)

Great, thank you both. I will get busy.