tach not working

#1

Well, it’s sorta working. When I start the car it works for about 2 seconds and
then drops down to 0 and works no more. Any ideas?

thanks,
Steven

#2

Batteries? The tach, fuel econ (vac) and I think the temp all run off the battery pack on the circuit board. If it’s just the tach, then it may be a little harder to diagnose. I just went through this frustration on mine and it turned out to be a bum circuit board (the one across the bottom of the cluster). The only thing that didn’t work was the tach/vac gauge.
Through my research, I found out you can use any of the parts out of any dash to fix it. The only thing that determines the tach sweep is the removable module in the bottom right of the cluster facing the driver. You can use an eta tach, just have to change the ‘paper’ face to the correct numerals.
It’s been said that the different brand name clusters don’t swap parts, but we didn’t find that to be the case, and I think that myth is ‘busted’.

#3

I have parts for 2 clusters if parts are needed. 2 working circuit boards as well

#4

I’ve got new batteries for the SI board. I’m going to charge them overnight
and install tomorrow. I’ll post results…

Steven

#5

let us know…where and what kind of batteries did you get?

#6

I replaced the batteries (on a different SI board) and still the same symptoms. I believe that this is related to other electrical gremlims that I’ve found. First was two weeks ago when I got ready to load the car on the trailer to take to paint - it would not turn over. Since the car was an auto, I quickly figured out that the Neutral safety relay was not clicking in. I tried a new relay - that did not work. I then removed the relay and put a jumper in to get the car started. That seemed odd to me since the car had started fine earlier that morning.

Now this morning, I noticed that my defroster fan is not working. Well it is working, but just like the tach. It works 1-2 seconds after startup and then quits with the tach. There is no lights on the SI board either.

The gas gauge is not working either…

Any ideas?

P.S. Pelical Parts has a detailed write up on how to change batteries on SI boards. I got to AA NiCd batteries from Radio Shack as replacement for the Varta batteries.

#7

As crazy as it sounds, verify all the ground connections in the Bentley Manual.
Actually loosen then retighten them and look for corrosion.
Look at the fuse block as well. I recall there was a car at VIR, (Jon Macavoy) I think that had some corrosion/wiring issues in the fuse block under the hood.

#8

Steven540i wrote:

[quote]Now this morning, I noticed that my defroster fan is not working. Well it is working, but just like the tach. It works 1-2 seconds after startup and then quits with the tach. There is no lights on the SI board either.

The gas gauge is not working either…
[/quote]

Check fuse #10 – it sounds exactly like my symptoms (do your water temp and MPG gauges work?)

then die… then the tach would sometimes work above 3k rpm (I’m glad I put a second tach on the a-pillar bar). Turns out that my giubo had chewed through my reverse switch wiring, which was blowing fuse #10.

#9

Found it after trying the different SI board to no avail.

thanks,
Steven

#10

Steven540i wrote:

[quote]Found it after trying the different SI board to no avail.

thanks,
Steven[/quote]
Great…fuse 10 is the culprit then. I need to put that in the memory banks.