Bad tach signal?

[veector]

Had this problem for some time now, I swapped out clusters but it didnt go away.  The rpm reads double what it should (idle just under 2000)  This causes the tach to roll past redline when i drive causing the entire cluster to shudder and reset.  any ideas what this could be?  

cheers,

Vic



btw 1994 Jetta TD

[Turftech]

I think the tach uses a signal from the alternator.  You might want to check it. 

[veector]

put a used alternator in a few months ago so I dont think thats the issue?  What could cause the tach to read double the revs?

[Settings]

I assume you have a gas tach. The signal from the alternator is essentially twice the frequency of that from the distributor (where the gas tach normally reads from).

There are several solutions provided on this forum from people much more knowledgeable than myself.
Start in the FAQ under 'Tach'  http://www.vwdiesel.net/forum/index.php?topic=16687.0

[veector]

Thing is though, I have a diesel tach, but a gas alternator.  if it makes any difference.  Il do some reading there too

cheers

vic

[doonboggle]

Maybe this discussion will help ...
http://www.thetruckstop.us/forum/showthread.php?14489-whats-the-difference-between-diesel-and-gas-alternators

Had this problem for some time now, I swapped out clusters but it didnt go away.  The rpm reads double what it should (idle just under 2000)  This causes the tach to roll past redline when i drive causing the entire cluster to shudder and reset.  any ideas what this could be?  

cheers,

Vic



btw 1994 Jetta TD