1990 Tach
Thread Starter
5th Gear
Joined: Jul 2005
Posts: 5
Likes: 0
From: Linton Indiana
1990 Tach
Hello all
I've got a '90 Corvette that I've had for about a month. The tachometer is acting up or just doesnt work. I dont know much about tachs and cant really find much info in the manuals. Here's the gripe, upon startup tach maxs out and returns to zero. No further action after that. Any help is surely appreciated. Thanks.
Dave
I've got a '90 Corvette that I've had for about a month. The tachometer is acting up or just doesnt work. I dont know much about tachs and cant really find much info in the manuals. Here's the gripe, upon startup tach maxs out and returns to zero. No further action after that. Any help is surely appreciated. Thanks.
Dave
Melting Slicks
Joined: Aug 1999
Posts: 2,240
Likes: 42
From: Baltimore, MD USA
Most likely the tach filter or the Dash Cluster is bad.
To determine where the problem is, you need to look at the tach signal with a scope. Should see a square wave at the output of the tach filter and the frequency increases with engine rpm.
If you don't have a scope I suggest you replace the tach filter.
If you look at the distributor cap on the driverside there is a bump out on the side of the cap. There are two push on connectors. I believe there are some letters etched in the Distributor Cap. One is marked Battery, the other wire a white one is marked Tach. If you follow the white wire, it goes to the tach filter.
The tach filter looks like a small cylinder with a metal bracket that bolts to one of the engine to transmission bell housing bolts.
Go to this site and you can see a picture of it.
http://www.corvettecentral.com
Search on part #393125
To determine where the problem is, you need to look at the tach signal with a scope. Should see a square wave at the output of the tach filter and the frequency increases with engine rpm.
If you don't have a scope I suggest you replace the tach filter.
If you look at the distributor cap on the driverside there is a bump out on the side of the cap. There are two push on connectors. I believe there are some letters etched in the Distributor Cap. One is marked Battery, the other wire a white one is marked Tach. If you follow the white wire, it goes to the tach filter.
The tach filter looks like a small cylinder with a metal bracket that bolts to one of the engine to transmission bell housing bolts.
Go to this site and you can see a picture of it.
http://www.corvettecentral.com
Search on part #393125
Last edited by Hooked on Vettes; Sep 13, 2005 at 08:05 PM.
LS/MFT
Joined: Jun 2000
Posts: 5,874
Likes: 0
From: Cary IL
St. Jude Donor '09-'10-'11-'12
Originally Posted by Hooked on Vettes
If you follow the white wire, it goes to the tach filter.
The tach filter looks like a small cylinder with a metal bracket that bolts to one of the engine to transmission bell housing bolts.
The tach filter looks like a small cylinder with a metal bracket that bolts to one of the engine to transmission bell housing bolts.
Sorry I went out to my '90 in the garage, and sure enough, there's a filter between the distributor and the C100 connector. Not only not shown in the wiring diagram, not mentioned as a possible issue in the tachometer diagnosis on 8A-82-14. I even thot I had all the updates. I wonder if there's one for this?
