Author Topic: Tach Question (Read 4186 times)

dubdiesel1 · « **on:** May 03, 2009, 07:58:02 am »

Guys, here is another tach question. The tach in my 91 Jetta TD will only come up to 250 RPMs, when engine is running, when the key is turned off the needle falls back to the peg. Every now and then it will begin to read accurately for 20 or 30 miles, before it falls back to 250 RPMs again.

I have checked and cleaned all the wiring from the "w" connection into the car and replaced the spad connections in the harness which attachs to the altenator and the wiring harness to insure clean connections.

The tach worked fine until the altenator stopped charging and I had to replace it. I have tried two new rebuild altenators, which both charge ( around 13.7 volts), but with both new altenators I am having this same tach problem.

Is it possible that I could have gotten two rebuild altenators from the local parts store which will charge, but will not be sending the correct signal to the tach?

I dont think the problem is in the dash itself. All lights, speedo, fuel gauge, etc works perfect except for the tach.

Any thoughts?

jettabrendan · « **Reply #1 on:** May 03, 2009, 09:40:02 am »

My cars do this while the belt is squealing. Your belt might be toast or too loose. Rev it while its in neutral and are if it catches. My money is on your belt.

jettabrendan · « **Reply #2 on:** May 03, 2009, 09:48:09 am »

And make sure your blue exciter wire is hooked up to the right prong.

dubdiesel1 · « **Reply #3 on:** May 04, 2009, 05:13:56 am »

Belts is new an tight. Problem is in the Altenators, both new and neither one is charging. Drove the car 30 miles yesterday and the tach fell to 0, checked the new altenator with a mulitmeter when I got home and it is not charging at all.

Should have the third replacement on tuesday.

Vincent Waldon · « **Reply #4 on:** May 04, 2009, 08:00:17 am »

Two dead ones in a row does sound a little strange though.

Does the "Batt" light on the dash come on when you turn the key to "on", and then go off when you start the car ?

If not, your alternator is not receiving the necessary excitation voltage from the cluster and won't be able to start generating electricity on its own. This will also mean that the tach won't work.

dubdiesel1 · « **Reply #5 on:** May 04, 2009, 11:43:41 am »

The battery light does come on when the key is turned on and it stays on after the engine starts until the normal throttle blip.

Vincent Waldon · « **Reply #6 on:** May 04, 2009, 11:59:46 am »

Okey dokey.... that means the wiring to the alternator is fine.

Hmmmm... third time's a charm ?! :wink: