I know this had been asked 10000 times, but i did a search and couldnt find anything helpful. My tach, when i start my car, will jump all the way up, stay for a couple seconds, then just drop alllll the way down and not move again. What are some troubleshooting options to maybe figure out what is up? Thanks for any information in advance!

Eric, 1990 Vert A4

 

According to Killebrew the most common problem is water in the bulkhead connection. Two other could be problems are a bad tach filter
or a bad ground, and if the tranny has been out lately it could be they didn't reconnect the ground strap.

 

When I had problems with my tach it turned out to be water in the bulkhead connection but mine did not behave exactly as you describe. Mine would do as you say when I started but then once underway, mine would continue to jump up and down for some time before finally settling down provided I drove far enough. It usually took 30 to 45 minutes of driving to ettle down.

 

My tach runs about 2k higher than it should, it not engine speed just electrical. I have read the solutions but I am unsure what the bulkhead is? I have had some water leak problems.
Please help, thanks

 

So how could I fix this bulkhead problem? And I've searched for a tach filter, but I couldnt find one for a 90, it only went up to 89. TIA

 

I recently replaced my tach filter. Matter of fact yesterday I opened up all the connections (you have to splice them in) which originally I used the crimp connects, I clipped them clean and solder the connections instead.

Anyway my tach filter cause or perhaps I should say it exposed a cascading sets of events. I had a number of things going on suddenly, the ECM would heat soak and start causing the engine to buck and die, a new ignition coil would not work with the new coil or another new coil but the old one would, no start with the new one start with old, and that was due to the tach filter. Once I spliced in a new tach filter, at which time I also spliced in a new ignition coil module connector, the new ignitiion coil module would now work with the coil and fire the engine. Following that I was now able to deal with the ECM issue.

Bottom line, the tach filter not only caused the ignition coil module not to work with the other components but it caused my tach to jump wildy. Peg the limits, zero then jump all over irratically.

Tach filter was something like $34. from Ecklers.

Picture from yesterday almost done two more splices to cut and solder.

Noted the picture but this is about half way done.


Finished ready to install.


After connection are made tied off the tach filter from the coolant hose.


First time when I spliced it in. Two of the leads were 6' long as they would normally route back through all the wiring harness then to the tach and to the ETBCM. One of the long wires had a spade (pink one if I remember) and the other had a pin to insert into the ETBCM connector. I spliced them instead.