low rev tachometer
Thread Starter
Racer
Joined: May 2009
Posts: 286
Likes: 11
From: LA CA
low rev tachometer
I recently got a tach from an 82 and was told it was compatible. My car is a 79, After I installed it, it only goes up to 3000 RPM's even when parked and accelerated. The needle is a lot more stable than the one I had in the car before, Reason why I changed it in the first place.
Do You guys think this unit is not compatible? The unit that came with the car used to red line... Any advise is greatly appreciated as allways....
Thank You in advance.....
Do You guys think this unit is not compatible? The unit that came with the car used to red line... Any advise is greatly appreciated as allways....
Thank You in advance.....
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
Your car has the GM H.E.I. ignition; the '82 had an ECU [computer]. 1980-82 C3's had a tachometer circuit board that is different from 78-79 models.
You need advice from an 'expert' on how to make that speedo work properly in your car.
You need advice from an 'expert' on how to make that speedo work properly in your car.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,847
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
The tach should have worked just fine! The difference in the 1978-1979 board from the 1980-1982 boards with GM was the relief cut in it for the light and of coarse the calibration.
This issue could be in the analog movement of the tach itself, the input signal breaking down at 3000, a cap on the board not bleeding off (don't ask me how I know this one), a tach filter problem, and or a few other issues.
You can eliminate just about all issues to do with the car by hard wiring the tach to the car.
Run a signal wire from the tach to the distributor, run power and a ground. While holding the tach in your hand, fire up the car and see if the tach responds the same way. If it does the problem is more than likely in the tachometer and not the car. (the only exception would then be the distributor)
I can test this for you too.. it's no charge except for the return shipping.
Willcox
This issue could be in the analog movement of the tach itself, the input signal breaking down at 3000, a cap on the board not bleeding off (don't ask me how I know this one), a tach filter problem, and or a few other issues.
You can eliminate just about all issues to do with the car by hard wiring the tach to the car.
Run a signal wire from the tach to the distributor, run power and a ground. While holding the tach in your hand, fire up the car and see if the tach responds the same way. If it does the problem is more than likely in the tachometer and not the car. (the only exception would then be the distributor)
I can test this for you too.. it's no charge except for the return shipping.
Willcox
Thread Starter
Racer
Joined: May 2009
Posts: 286
Likes: 11
From: LA CA
not jump or skips but does not red line.. By the way it does go more than 3000 RPM if I push it really hard so it is not stopping @ 3000 RPM
exactly..
Have in mind that I only ask because I do not know what is causing this... Thank You for the reply..
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,847
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
I really don't see contradiction here, I think 71 was just offering the thought of the computer controlled 82 as maybe being the problem.
The 1982 cars had a white wire on circuit 121 that plugs in to the distributor and runs from the distributor straight to the tach plug connection at the printed circuit. The only other item in line between the distributor and the tach is what is called the tach filter.
The tach boards both use the exact same signal on the 1978-1979 and the 1980-1982 but you can not switch a board from a 1978-1979 and use it on a 1980-1982 without calibration. The key here is the face of the tach is incremented differently requiring different calibration.
Willcox
The 1982 cars had a white wire on circuit 121 that plugs in to the distributor and runs from the distributor straight to the tach plug connection at the printed circuit. The only other item in line between the distributor and the tach is what is called the tach filter.
The tach boards both use the exact same signal on the 1978-1979 and the 1980-1982 but you can not switch a board from a 1978-1979 and use it on a 1980-1982 without calibration. The key here is the face of the tach is incremented differently requiring different calibration.
Willcox
