TACH acting weird
Thread Starter
Heel & Toe
Joined: Jul 2009
Posts: 16
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TACH acting weird
1978 Corvette
When I turn off the car the TACH moves past the 70 rpm point and is "stuck" until I either hit a bump or rev it up hard one time. Nothing too bad, just annoying. What's the fix? :-)
Kim
www.millersservices.com\toys\toys.htm
Was going to post pic but it won't give me that option?? Grr
When I turn off the car the TACH moves past the 70 rpm point and is "stuck" until I either hit a bump or rev it up hard one time. Nothing too bad, just annoying. What's the fix? :-)
Kim
www.millersservices.com\toys\toys.htm
Was going to post pic but it won't give me that option?? Grr
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,853
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Hi Kimmiller-
After you rev up the engine does the tach start working fine?
It sounds like something is spiking the signal going to the tach. It could be loose wire at the distributor, or another wire loose and spiking the tach circuit.
The tach when turned off should hold the last RPM reading it had. When you turn the key to the on position it should go to zero.
I would check the wires at the tach filter. This is the little capacitor bolted to the intake manifold on your car. It will be on the driver side and it will have a running up to the tach connector on the distributor cap. Check the wire at the distributor, check the wires where they go in to the filter, and check them at the harness connection.
This could also be a problem in the connection at the back of the speedo tach cluster housing. Possibly one of the fingers on the printed circuit is loose and hitting the tach signal wire. I’ve not done any testing for this symptom!
You can eliminate or prove the tach as the problem by removing it from the car and hardwiring it. I did a video on U tube that will show you exactly how to do this. If you hardwire the tach and get the same symptoms, then it is in the tach board and not the car.
On your car tach removal is a 10 minute job! You simply remove the lens cover from the speedo tach housing and then remove the three bolts that are holding the tach in the housing. This will allow you to pull the tach out from the front without taking anything else loose. It is very easy. Post again if you feel up to the task! I’ll post you the U-tube link and you can see how to hardwire it for testing.
Willcox Inc.
Hardwire the tach on these post when removed.
Here is a page if you want to remove the speedo and tach housing to get to the connector on the back.
http://willcoxcorvette.com/repairand...lp.php?hID=146
Here is a link if you need to install the tach board.
http://willcoxcorvette.com/repairand...lp.php?hID=252
Here is the board install video.
After you rev up the engine does the tach start working fine?
It sounds like something is spiking the signal going to the tach. It could be loose wire at the distributor, or another wire loose and spiking the tach circuit.
The tach when turned off should hold the last RPM reading it had. When you turn the key to the on position it should go to zero.
I would check the wires at the tach filter. This is the little capacitor bolted to the intake manifold on your car. It will be on the driver side and it will have a running up to the tach connector on the distributor cap. Check the wire at the distributor, check the wires where they go in to the filter, and check them at the harness connection.
This could also be a problem in the connection at the back of the speedo tach cluster housing. Possibly one of the fingers on the printed circuit is loose and hitting the tach signal wire. I’ve not done any testing for this symptom!
You can eliminate or prove the tach as the problem by removing it from the car and hardwiring it. I did a video on U tube that will show you exactly how to do this. If you hardwire the tach and get the same symptoms, then it is in the tach board and not the car.
On your car tach removal is a 10 minute job! You simply remove the lens cover from the speedo tach housing and then remove the three bolts that are holding the tach in the housing. This will allow you to pull the tach out from the front without taking anything else loose. It is very easy. Post again if you feel up to the task! I’ll post you the U-tube link and you can see how to hardwire it for testing.
Willcox Inc.
Hardwire the tach on these post when removed.
Here is a page if you want to remove the speedo and tach housing to get to the connector on the back.
http://willcoxcorvette.com/repairand...lp.php?hID=146
Here is a link if you need to install the tach board.
http://willcoxcorvette.com/repairand...lp.php?hID=252
Here is the board install video.
Last edited by Willcox Corvette; Jul 27, 2009 at 07:59 PM.
