Tach reads double on 1991, why??

[*89x2*]

Title says it all - tach reads 2x's what it should, at any given RPM - any ideas???

TIA!

 

[KANE]

Title says it all - tach reads 2x's what it should, at any given RPM - any ideas???

TIA!

Sounds like an electrical Gremlin...

I had a similar issue with a tach using HEI on my 1978.

I think you have a higher than usually level of voltage coming through the primary signal lead, making the value greater and the readings higher. So, you have either a bad connection somewhere or a bad tachometer.

Start checking your wires from the DIS (or HEI- the logic is the same) to the tach. Begin with the the coils- perhaps the tach lead has become damaged somehow. If it is the tach, you'll need to test it against the right voltage at any given RPM and see if the reading is correct. If the rpms are not correct at the right voltage, the "guts" in the tach are shot.

 

[Wegone]

I believe there is a resistor or filter that goes bad on the back of the tach..Anyway you will need to remove the cluster to have it fixed. Check on the ZR1 net they had an article about it. By the way had a 90 do the same thing.

http://forums.corvetteforum.com/showthread.php?t=1380190&highlight=C4+tach+issues