Author Topic: rpm/tachometer gauge messing up (Read 3650 times)

Clintwalker85 · « **on:** April 02, 2009, 11:49:11 pm »

i got a mk3 aaz td and my rmp gauge just started messing up it will sit around 2000rpm at idle and max out sometimes when i step on the gas also i notice when i turn on the heater and lights it will go up and down...i thought it was a ground but i checked them all and added more still makes no difference any one have any tips?

burn_your_money · « **Reply #1 on:** April 03, 2009, 04:47:57 am »

MK3s are well known for having bad electronics. The gauge cluster is probably top of the list. I've taken one apart before, and it's rather complex in there.

Clintwalker85 · « **Reply #2 on:** April 05, 2009, 12:09:49 am »

anything else it might be?

Vincent Waldon · « **Reply #3 on:** April 05, 2009, 10:56:31 am »

If it's just the tach, and the symptoms change as you change the load on the alternator, then there's a good chance the problem lies with the alternator itself (since that's also where the RPM signal is coming from).

I've seen this movie once before and the issue was the alternator was starting to give out... not so much that the battery didn't stay charged, but enough that the tach output was flakey. A voltmeter on the alternator might be a good next step, particularly if you can watch the alternator output when the tach misbehaves.

Having said that... if the cluster itself shows any other strange behaviors... specifically if the speedo starts to misbehave as well, then the problem is 99.99% of the time a dying cluster and replacement is pretty much the only option... no user-maintainable parts, no schematics available, and it's never ever just a ground or solder connection. Ever. :wink:

Clintwalker85 · « **Reply #4 on:** April 06, 2009, 01:46:43 am »

ok thanks i will try that i just put in a brand new bosch alternater 3 months ago abut it seems everything affects it turn on the heat radio wipers even signal lights make the tach jump around