Tachometer Issue + Dash Grounds

**MitchW** · #1 (**permalink**) 10-03-2006, 01:09 PM

I finally got around to pulling the dash and it was far easier then I thought it would be. I pulled the connectors and tightened the contacts and used contact cleaner but my tachometer is still mostly dead. It'll only go up to about a 1000 rpm on the highway. I've already cleaned the connectors and grounds under the hood.

Are there some grounds inside the dash I need to look next and where are they located?

Is there anything else I can do?

Mitch

**alfaparticle** · #2 (**permalink**) 10-03-2006, 07:07 PM

My tach is useless too. I read that there is a calibration potentiometer that develops a bad contact resistance. You probably have to work it around a bit then set it to give correct readings against a calibrated tachometer.

What is involved in getting the dash off to give access to the tacho? I am interested in getting mine right.

Ed Prytherch, Columbia SC
88 verde

**Gubi** · #3 (**permalink**) 10-03-2006, 07:33 PM

This site has a procedure for pulling and adjusting the Milano tach.

http://www.alfaclub.org/techstff/tacho.htm

**kredden** · #4 (**permalink**) 10-04-2006, 06:49 AM

The only grounds I know of back there are behind the fuse box, see Where are the grounds under the dash on drivers side?

Kevin

**MitchW** · #5 (**permalink**) 10-04-2006, 10:08 AM

I forgot to mention a couple of items that make me suspect the grounds first.

The tach will occasionally start reading higher. Close to correct at idle but lower above that.

Secondly the fuel and temperature guages read higher with the lights turned on. If I work the instrument light resostat you can watch the needles go up and down.

Lastly the speedometer reads correctly in the morning and the 5-8mph slower in the afternoon regardless of the temperature.

I'll look for the ground behind the fusebox and I suppose I may as well clean the fusebox as well.

**alfaparticle** · #6 (**permalink**) 10-04-2006, 12:26 PM

Hey Mitch,
Those are cool symptoms. My ARC sometimes flashes in synch with the music from the radio. Only on a Milano!

Ed Prytherch, Columbia SC
88 Verde
79 Spider
74 GTV

**MitchW** · #7 (**permalink**) 10-05-2006, 07:56 AM

Not so cool from my view. Not being able to trust the guages makes me nervous. Is that high temp reading overheating or just a glitch? Am I legal when I'm driving past that radar unit or not? Am I about to run out of gas?

**Gubi** · #8 (**permalink**) 10-05-2006, 09:51 AM

Quote:

Originally Posted by MitchW

Is that high temp reading overheating or just a glitch? Am I legal when I'm driving past that radar unit or not? Am I about to run out of gas?

**alfaparticle** · #9 (**permalink**) 10-05-2006, 10:12 AM

Mitch:
If your grounds are good then you may have a high resistance in a 12 volt supply circuit that causes voltage variations at the instruments. Could you run a temporary direct wire from the battery to the instruments (switched so that you don't drain the battery)? If it "fixes" the problems then you will know where to focus your efforts.
Sorry if my humor was off base.
Ed

**MitchW** · #10 (**permalink**) 10-05-2006, 10:24 AM

I didn't mind your humour but I am a bit frustrated. Thanks for the suggestion I'll give it a try.

PS: My daughter also thinks the ARC flashes with the beat of the music. When my radio wasn't working I tried a portable radio and it picked up interference that was the same frequency as the ARC. Probably the alternator.

**MitchW** · #11 (**permalink**) 10-09-2006, 07:42 AM

Yahoo sucess! I cleaned up all the contacts behind the fusebox (didn't find any grounds) and my tach is alive. It still reads about 300rpm low at 3000 but that should be easy to adjust when I get the chance.

I did dicover that I've been short shifting using my ear. What's amazing is how much torque there is down low, especially listening to the discussions on the AlfaBB. My Verde has the S cams and slightly advanced timing and I don't think I'll find many places where I can hit red line. OTOH my other Alfa is a Spider Jr. with 1300 glorius cc's (you can hit red line just about anywhere without worrying about being too illegal).

Mitch