fuel gauge question
Thread Starter
Burning Brakes
Joined: Dec 2004
Posts: 825
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From: Hanging out back with the dark horses. Wa.
fuel gauge question
81 Vett, new tank, sending unit, gauge looks good, new printed board.
filled new tank 25 gal. gauge reads 1/4. pull sending unit wire at tank goes to full. pull ground wire at unit and it does nothing. power off does nothing.
Ground issue?....I'm lost here
filled new tank 25 gal. gauge reads 1/4. pull sending unit wire at tank goes to full. pull ground wire at unit and it does nothing. power off does nothing.
Ground issue?....I'm lost here
Instructor
Joined: Jun 2010
Posts: 199
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sounds like a ground or a short issue mine did that till i recently dropped the tank and took a wire brush to the ground terminal and cleaned it up it was a rusted mess mine wasa 77 though.
maybe also a break in the wire to the sending unit when you move it your closing the break.
maybe also a break in the wire to the sending unit when you move it your closing the break.
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Now do the other half of that test,"ground the sending unit wire", the needle should go to empty. If the needle does go to empty your wiring and dash gauge are OK.
If grounding the sending unit wire "does not" send the needle to empty then you probably have a dash gauge or cluster wiring problem.
If grounding the sending unit wire "does not" send the needle to empty then you probably have a dash gauge or cluster wiring problem.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,851
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
I think this will help you a ton! And Roger 
actually had a huge amount of input on this I wrote it for the 68-76 cars.
Corvette Fuel Gauge and Sending Unit Testing 1977-1982
Also, just a side note to this: Two things come to mind that should be mentioned but I'm hoping number 2 is not your problem. Number 1 can be eliminated with a ground test.
1) In All Cases, if the resistor on the back of the dash unit is missing or defective the highest reading the gauge can produce is slightly higher than 1/4 of a tank.
2) Another one from the been there done that file (twice actually in the past two years). The gas tanks on the 78-82 cars have a bladder lining in them. This bladder can crack and allow fuel to move between the steel tank and the bladder. When this happens the bladder can push outward and interfer with the float on the sending unit.
But as Roger mentioned, you need to ground out the gauge and see what it does first. This will eliminate the resistor on the back of the gauge.
actually had a huge amount of input on this I wrote it for the 68-76 cars. Corvette Fuel Gauge and Sending Unit Testing 1977-1982
Also, just a side note to this: Two things come to mind that should be mentioned but I'm hoping number 2 is not your problem. Number 1 can be eliminated with a ground test.
1) In All Cases, if the resistor on the back of the dash unit is missing or defective the highest reading the gauge can produce is slightly higher than 1/4 of a tank.
2) Another one from the been there done that file (twice actually in the past two years). The gas tanks on the 78-82 cars have a bladder lining in them. This bladder can crack and allow fuel to move between the steel tank and the bladder. When this happens the bladder can push outward and interfer with the float on the sending unit.
But as Roger mentioned, you need to ground out the gauge and see what it does first. This will eliminate the resistor on the back of the gauge.
Last edited by Willcox Corvette; Jul 28, 2010 at 05:05 PM.
Thread Starter
Burning Brakes
Joined: Dec 2004
Posts: 825
Likes: 0
From: Hanging out back with the dark horses. Wa.
Now do the other half of that test,"ground the sending unit wire", the needle should go to empty. If the needle does go to empty your wiring and dash gauge are OK.
If grounding the sending unit wire "does not" send the needle to empty then you probably have a dash gauge or cluster wiring problem.
If grounding the sending unit wire "does not" send the needle to empty then you probably have a dash gauge or cluster wiring problem.
New tank, no bladder in it.
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,851
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Well that's good news.. go upload this, it's free and I think it will help you if grounding the gauge results in an empty gauge. But the 1/4 tank thing keeps telling me it's a resistor problem.
The only way this would not be true would be if the gauge just happened to be in that position when it was shut down and you have a dash gauge grounding problem. If the dash ground is missing from this gauge it will kind of just stay where it's at with no movement. Again, your grounding out test will eliminate this as a problem if the gauge functions with the ground out test.
http://willcoxcorvette.com/repairand...lp.php?hID=277
Willcox
The only way this would not be true would be if the gauge just happened to be in that position when it was shut down and you have a dash gauge grounding problem. If the dash ground is missing from this gauge it will kind of just stay where it's at with no movement. Again, your grounding out test will eliminate this as a problem if the gauge functions with the ground out test.
http://willcoxcorvette.com/repairand...lp.php?hID=277
Willcox
Last edited by Willcox Corvette; Jul 28, 2010 at 06:51 PM.
Thread Starter
Burning Brakes
Joined: Dec 2004
Posts: 825
Likes: 0
From: Hanging out back with the dark horses. Wa.
Well that's good news.. go upload this, it's free and I think it will help you if grounding the gauge results in an empty gauge. But the 1/4 tank thing keeps telling me it's a resistor problem.
The only way this would not be true would be if the gauge just happened to be in that position when it was shut down and you have a dash gauge grounding problem. If the dash ground is missing from this gauge it will kind of just stay where it's at with no movement. Again, your grounding out test will eliminate this as a problem if the gauge functions with the ground out test.
http://willcoxcorvette.com/repairand...lp.php?hID=277
Willcox
The only way this would not be true would be if the gauge just happened to be in that position when it was shut down and you have a dash gauge grounding problem. If the dash ground is missing from this gauge it will kind of just stay where it's at with no movement. Again, your grounding out test will eliminate this as a problem if the gauge functions with the ground out test.
http://willcoxcorvette.com/repairand...lp.php?hID=277
Willcox
Thread Starter
Burning Brakes
Joined: Dec 2004
Posts: 825
Likes: 0
From: Hanging out back with the dark horses. Wa.
I think this will help you a ton! And Roger actually had a huge amount of input on this I wrote it for the 68-76 cars.
Corvette Fuel Gauge and Sending Unit Testing 1977-1982
Also, just a side note to this: Two things come to mind that should be mentioned but I'm hoping number 2 is not your problem. Number 1 can be eliminated with a ground test.
1) In All Cases, if the resistor on the back of the dash unit is missing or defective the highest reading the gauge can produce is slightly higher than 1/4 of a tank.
2) Another one from the been there done that file (twice actually in the past two years). The gas tanks on the 78-82 cars have a bladder lining in them. This bladder can crack and allow fuel to move between the steel tank and the bladder. When this happens the bladder can push outward and interfer with the float on the sending unit.
But as Roger mentioned, you need to ground out the gauge and see what it does first. This will eliminate the resistor on the back of the gauge.
actually had a huge amount of input on this I wrote it for the 68-76 cars. Corvette Fuel Gauge and Sending Unit Testing 1977-1982
Also, just a side note to this: Two things come to mind that should be mentioned but I'm hoping number 2 is not your problem. Number 1 can be eliminated with a ground test.
1) In All Cases, if the resistor on the back of the dash unit is missing or defective the highest reading the gauge can produce is slightly higher than 1/4 of a tank.
2) Another one from the been there done that file (twice actually in the past two years). The gas tanks on the 78-82 cars have a bladder lining in them. This bladder can crack and allow fuel to move between the steel tank and the bladder. When this happens the bladder can push outward and interfer with the float on the sending unit.
But as Roger mentioned, you need to ground out the gauge and see what it does first. This will eliminate the resistor on the back of the gauge.
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Race Director
Joined: May 2006
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From: Dayton, Ohio
If you grounded the sending unit wire and the needle went to empty and ungrounded the wire and the needle went to full the resistor should be OK.
Sounds to me like your problems are at the tank.
Sounds to me like your problems are at the tank.
Thread Starter
Burning Brakes
Joined: Dec 2004
Posts: 825
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From: Hanging out back with the dark horses. Wa.
No... it went to 1/4 again. if I pull the sending unit wire off it goes to full. ground it ..goes to E, hook it all up the way it should it stays at 1/4. info willcox gave shows possible reistor issue... I think
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,851
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Ok.. so it didn't pass the grounding test at the tank. Have you had the cluster out of this car before?
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,851
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
That's what I took it as... kind of confusing though.
Thread Starter
Burning Brakes
Joined: Dec 2004
Posts: 825
Likes: 0
From: Hanging out back with the dark horses. Wa.
still having issues with the fuel gauge. drove the car some to burn off some fuel. Now the guage is moving even lower 1/4 tank reading. tank has about 1/2-3/4 of fuel.
sending unit issue? it new also
sending unit issue? it new also
