C4 Tachometer
Thread Starter
4th Gear
Joined: Aug 2013
Posts: 4
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C4 Tachometer
My tachometer on my 1991 C4 has not worked since I bought it. I read somewhere that it may be the filter. I tried to jumper across the filter wires but somehow must have screwed up since now my "one to four" light is on all the time. Does anyone know how to 1) get the light back off 2) help me to get the tach working
Cruising
Joined: Mar 2013
Posts: 14
Likes: 0
From: Tomball Texas
There is a plug under the distributor, the connector is brown in color. Check that, if thats plugged in then the tach portion of the distributor is bad or dash cluster is messed as well. My 91 is having the same problem.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Maybe the circuitry changed on later L98s (I doubt it), so...
The tach signal that the dashboard uses comes from the distributor cap. It's the white wire. That goes to the tach filter and then to the dashboard.
The tach signal that the dashboard uses comes from the distributor cap. It's the white wire. That goes to the tach filter and then to the dashboard.
Safety Car
Joined: Jan 2004
Posts: 3,556
Likes: 13
If you have no tacho at all, you should use a DVM to see if you have continuity on the wire from the coil (dist cap ) to the cluster connector
Then when you get it working you may find other problem common to 90/91 GM tachos
http://forums.corvetteforum.com/c4-g...ch-repair.html
Then when you get it working you may find other problem common to 90/91 GM tachos
http://forums.corvetteforum.com/c4-g...ch-repair.html
Team Owner
Joined: Sep 2003
Posts: 25,366
Likes: 2,732
Use a scanner and see if there's a tach reference available on the scanner. If it works at the ALDL then the issue isn't at the distributor. If the A/C is C68 you could also use the digital readout on the A/C control to check the RPMs. If it's a C60 car there's nothing other than using the ALDL. Without checking the FSM I believe this is the correct procedure for using the C68. I don't believe I've used it for 6 or so years. This single post should be correct:
http://forums.corvetteforum.com/1577429729-post3.html
http://forums.corvetteforum.com/1577429729-post3.html
Team Owner
Joined: Sep 2003
Posts: 25,366
Likes: 2,732
See the link in post# 5
Last edited by WVZR-1; Sep 6, 2013 at 10:29 AM.
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Burning Brakes
Joined: Mar 2010
Posts: 1,094
Likes: 68
From: Providence RI
my 1991 tach flutters around like crazy...when i datalog on datamaster, the rpms show up correctly. It's not your tach filter...the cluster needs to be worked on. Do all of the other guages work? My oil temp guage doesnt get above 105* even though that too displays correctly when i log my car.