Tachometer question???
Thread Starter
Racer
Joined: Aug 2011
Posts: 455
Likes: 7
From: Lewes Delaware
Tachometer question???
The tach on my '79 L48 is all the way to the right when the car is off. When I start it, the tach will jump up to the 12 o'clock position but returns to the full right spot after it starts. Does this sound like an electrical board problem? If so, I'm guessing Willcox can install a new board and recalibrate? Any help/suggestions appreciated.
Burning Brakes
Joined: Jan 2012
Posts: 943
Likes: 73
The tach on my '79 L48 is all the way to the right when the car is off. When I start it, the tach will jump up to the 12 o'clock position but returns to the full right spot after it starts. Does this sound like an electrical board problem? If so, I'm guessing Willcox can install a new board and recalibrate? Any help/suggestions appreciated.
Burning Brakes
Joined: Jul 2014
Posts: 831
Likes: 54
From: Arlington TX
The tach on my '79 L48 is all the way to the right when the car is off. When I start it, the tach will jump up to the 12 o'clock position but returns to the full right spot after it starts. Does this sound like an electrical board problem? If so, I'm guessing Willcox can install a new board and recalibrate? Any help/suggestions appreciated.
Thread Starter
Racer
Joined: Aug 2011
Posts: 455
Likes: 7
From: Lewes Delaware
Burning Brakes
Joined: Jul 2014
Posts: 831
Likes: 54
From: Arlington TX
Yeah.. the tach filter. Just bypass it and see if anything changes.
Burning Brakes
Joined: Jan 2012
Posts: 943
Likes: 73
Is it possible gravity is bringing the needle over to the full right after it starts? Did this problem just start? If the tach was ok, then started acting up, I don't think the needle position needs resetting. Tach boards do go bad as well as the unit pictured on the intake manifold.
The problem with the fuel gauge may be with the sender. It's been a long time but I think I disconnected the sending wire at the tank and the grounded it to see if the gauge read correctly.
The problem with the fuel gauge may be with the sender. It's been a long time but I think I disconnected the sending wire at the tank and the grounded it to see if the gauge read correctly.
Thread Starter
Racer
Joined: Aug 2011
Posts: 455
Likes: 7
From: Lewes Delaware
Is it possible gravity is bringing the needle over to the full right after it starts? Did this problem just start? If the tach was ok, then started acting up, I don't think the needle position needs resetting. Tach boards do go bad as well as the unit pictured on the intake manifold.
The problem with the fuel gauge may be with the sender. It's been a long time but I think I disconnected the sending wire at the tank and the grounded it to see if the gauge read correctly.
The problem with the fuel gauge may be with the sender. It's been a long time but I think I disconnected the sending wire at the tank and the grounded it to see if the gauge read correctly.
I'll try grounding the fuel gauge sending wire and see if that has any effect. Thanks for the suggestions and input.
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Thread Starter
Racer
Joined: Aug 2011
Posts: 455
Likes: 7
From: Lewes Delaware
I had time today to look around for a tach filter but there isn't one. The spot where yours is bolted to the manifold is empty. There is one white wire coming directly off of the distributer...maybe that's it tach wire?
Le Mans Master
Joined: Dec 2006
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(Yes, tach is white)
Former Vendor
Joined: Aug 2006
Posts: 76,656
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
The tach on my '79 L48 is all the way to the right when the car is off. When I start it, the tach will jump up to the 12 o'clock position but returns to the full right spot after it starts. Does this sound like an electrical board problem? If so, I'm guessing Willcox can install a new board and recalibrate? Any help/suggestions appreciated.
Willcox
Former Vendor
Joined: Aug 2006
Posts: 76,656
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From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
There is a video on our site about testing the fuel gauge and how to know what the issue is based on what the gauge does. Plus there is another page on there for helping you find the issue.
http://repairs.willcoxcorvette.com/1...el-gauge-test/
http://repairs.willcoxcorvette.com/w...it-testing.pdf
Thread Starter
Racer
Joined: Aug 2011
Posts: 455
Likes: 7
From: Lewes Delaware
If your fuel gauge is all the way to the right... you are missing ohms input to the gauge. Pull the sending unit wire from the sender and ground it out... if the gauge goes to empty then you have a fuel sending unit issue.
There is a video on our site about testing the fuel gauge and how to know what the issue is based on what the gauge does. Plus there is another page on there for helping you find the issue.
http://repairs.willcoxcorvette.com/1...el-gauge-test/
http://repairs.willcoxcorvette.com/w...it-testing.pdf
There is a video on our site about testing the fuel gauge and how to know what the issue is based on what the gauge does. Plus there is another page on there for helping you find the issue.
http://repairs.willcoxcorvette.com/1...el-gauge-test/
http://repairs.willcoxcorvette.com/w...it-testing.pdf
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,850
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
This is what you should have. By-pass the filter and plug the tach straight to the distributor and see if anything changes.
Thread Starter
Racer
Joined: Aug 2011
Posts: 455
Likes: 7
From: Lewes Delaware
It appears that the PO already did that (no tach filter found). So, my guess is that your first diagnosis of a bad board is correct. What is the cost if I send in my tach for your guys to install a new board and calibrate? Also, would I need a filter?
Burning Brakes
Joined: Jul 2014
Posts: 831
Likes: 54
From: Arlington TX
Not necessarily. It is indeed not mounted to the manifold. But It could be hanging loose on the back side our down below. But I will say that it is looking more and more likely to be a "grounding-out" issue.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,850
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Since the car is a 1979 removal is pretty easy and there are other diagnostic test you can perform before you send in the board.
First if you remove the tach / speedo lens cover from the tach / speedo housing and then remove the bezel. Once completed remove the three tach retaining screws... Here, go read this, it will walk you through the entire process.
1978-1982 Corvette Tachometer Testing, Removal, Board Installation
Once you have the tach out you should verify power and ground on the three tach clips.... Use another ground source to test the power terminal, then use the ground clip to test again. This will verify that you have power and ground at the tachometer. Once you have done this then test continuity from the signal clip to the connector that plugs in to the filter (or distributor if by-passed). This will verify the signal wire is good. You pass all three of these test then you do need a board.
Keep in mind a board is not a fix all and as the tach ages so do the internal analog movements so it is possible for you to purchase a board and not get fixed. If you send the tach in to us for the repair we can test the movement before we install a board and know if the issue is the board or movement.
Tach board installation:
1978-1979 Corvette Tach Board:
First if you remove the tach / speedo lens cover from the tach / speedo housing and then remove the bezel. Once completed remove the three tach retaining screws... Here, go read this, it will walk you through the entire process.
1978-1982 Corvette Tachometer Testing, Removal, Board Installation
Once you have the tach out you should verify power and ground on the three tach clips.... Use another ground source to test the power terminal, then use the ground clip to test again. This will verify that you have power and ground at the tachometer. Once you have done this then test continuity from the signal clip to the connector that plugs in to the filter (or distributor if by-passed). This will verify the signal wire is good. You pass all three of these test then you do need a board.
Keep in mind a board is not a fix all and as the tach ages so do the internal analog movements so it is possible for you to purchase a board and not get fixed. If you send the tach in to us for the repair we can test the movement before we install a board and know if the issue is the board or movement.
Tach board installation:
1978-1979 Corvette Tach Board:
Thread Starter
Racer
Joined: Aug 2011
Posts: 455
Likes: 7
From: Lewes Delaware
I checked that. The white signal wire exits the wire harness near the firewall and runs directly to the dist (nothing in between).