Tach Stuck at 2000
Thread Starter
Le Mans Master
Joined: Dec 2005
Posts: 8,564
Likes: 950
From: Communist Colorado
Tach Stuck at 2000
1982 ....Did some research on it, seems like the circuit board is the issue. Fuse is good, filter has been replaced. Funny thing is, although erratic, it was working.... mostly.... did a full tune up cap/rotor plugs, wires, FF.... now its stuck at 2000.... I double checked the connection at the distributor cap and its good also,,, Anything Im missing?
Le Mans Master
Joined: Sep 2002
Posts: 5,236
Likes: 898
From: Myrtle Beach SC
Back in the day I worked with Wilcox on his new tach boards for both 78-82 and the 75-77 boards. The view then was that 95% of the time the problem was the board. Here's an article from the C3s best mag ever, the Corvette Enthusiast on the topic of tach boards, with relevance to today. 
http://www.hunt4cleanair.net/Articles/tachboards.pdf
http://www.hunt4cleanair.net/Articles/tachboards.pdf
Thread Starter
Le Mans Master
Joined: Dec 2005
Posts: 8,564
Likes: 950
From: Communist Colorado
Update**
Ok, I replaced the board. Still stuck at 2000. I bypassed the filter. Still stuck at 2000. I connected 12 volts, ground and signal (off the distributor, with key on) test jumpers directly through the back of the tach pins. Still stuck at 2000. Im assuming the tach itself is fried.... Anything else?
Foot Note*** Reading the above article mentioned the fragility of the tach board and sensitivity to voltage spikes such as momentarily hooking up a charge cable to the wrong battery teriminal... I di remember when I was fighting the spark plug wire shielding on the passenger side, I hit the positive stud on the starter with my ratchet and sparked it pretty good. BUT, the gauge fuse didnt blow. Im not sure if thats what might have damaged the tach... but why wouldnt the fuse blow before taking out the tach?
Foot Note*** Reading the above article mentioned the fragility of the tach board and sensitivity to voltage spikes such as momentarily hooking up a charge cable to the wrong battery teriminal... I di remember when I was fighting the spark plug wire shielding on the passenger side, I hit the positive stud on the starter with my ratchet and sparked it pretty good. BUT, the gauge fuse didnt blow. Im not sure if thats what might have damaged the tach... but why wouldnt the fuse blow before taking out the tach?
Last edited by 81c3; May 13, 2023 at 02:10 PM.
Thread Starter
Le Mans Master
Joined: Dec 2005
Posts: 8,564
Likes: 950
From: Communist Colorado
Update
Just wanted to update my thread for people who search for this topic in the future.
I replaced the tach with a new AC Delco unit from Zip. Also replaced the filter at the same time for a good baseline.
Tach is now operational and seems pretty accurate out of the box.
I notice the tach will stay at the rpm the engine was last when you shut the car down. When I cycle the key again, it goes back to zero.
I believe this is normal behavior.
I replaced the tach with a new AC Delco unit from Zip. Also replaced the filter at the same time for a good baseline.
Tach is now operational and seems pretty accurate out of the box.
I notice the tach will stay at the rpm the engine was last when you shut the car down. When I cycle the key again, it goes back to zero.
I believe this is normal behavior.
