Fuel Guage
Thread Starter
Instructor
Joined: Jun 2012
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Fuel Guage
My fuel gauge isnt reading correctly.
I have checked the gauge itself is working correctly.
When i remove the pink wire off the sender unit the gauge goes past full, to about 4 o'clock.
When i put it back on it goes to near enough full when the tank is probably only half full.
I have checked the gauge itself is working correctly.
When i remove the pink wire off the sender unit the gauge goes past full, to about 4 o'clock.
When i put it back on it goes to near enough full when the tank is probably only half full.
Racer
Joined: Feb 2009
Posts: 330
Likes: 9
From: Las Vegas Nevada
My fuel gauge isnt reading correctly.
I have checked the gauge itself is working correctly.
When i remove the pink wire off the sender unit the gauge goes past full, to about 4 o'clock.
When i put it back on it goes to near enough full when the tank is probably only half full.
I have checked the gauge itself is working correctly.
When i remove the pink wire off the sender unit the gauge goes past full, to about 4 o'clock.
When i put it back on it goes to near enough full when the tank is probably only half full.
Last edited by Lil" Red Corvette; Dec 2, 2012 at 12:45 AM.
Racer
Joined: Feb 2009
Posts: 330
Likes: 9
From: Las Vegas Nevada
Can you measure the continuity between the black wire at the sending unit and the frame? Also, can you check to see if there is any voltage on the pink (tan) wire at the sending unit with the wire disconnected? My schematic shows that the two wires on the sending unit are tan and black. Hope you get this figured out because mine is doing the same thing. Where is the sending unit on yours. I can't see mine at all from under the car. I think I would have to drop the tank to get to it. I have to pull the rear bumper cover soon for another reason. Maybe I can get to it from the back.
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
Take an ohms reading on the sending unit and see what it is putting out. 0- empty, 90 full. If the sender is putting out 80-90 at 1/2 tank then I'd look hard at the sending unit as the issue.
You might take a look at the link below.
Corvette Fuel Gauge and Sending Unit Testing 1977-1982
And your gauge works just the same as this one.
You might take a look at the link below.
Corvette Fuel Gauge and Sending Unit Testing 1977-1982
And your gauge works just the same as this one.
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Racer
Joined: Feb 2009
Posts: 330
Likes: 9
From: Las Vegas Nevada
Yes, sounds like it. Are your tailights and things working on the back of the car? Not sure exactly where it is at but somewhere back there you have a main ground. Your goal is to be able to read 0 ohms (continuity) between the black wire and the frame. Right now your sending unit is trying to find a path to ground through your gas tank. This increased resistance will add to the 0-90 ohms that your sending unit provides to the circuit. This will cause exactly what you are describing. When your tank is half full the sening unit should be at 45 ohms. If the circuit path to ground is 40 ohms (just for example) you have a total circuit resistance of 85 ohms so the gauge thinks the tank is almost full. Hopefully this is your only problem. Please let us know what happens when you fix that ground. I'm especially interested because my car is doing the same thing.
Last edited by Lil" Red Corvette; Dec 2, 2012 at 10:22 PM.
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
Brady
When you touch the pink wire to the ground wire it should give you the same reading as when you ground the pink wire out.. or empty. The ground is the problem and Red is on it.. If.. when you touch the pink wire to the ground it goes to 4... you don't have continuity.. so the pink wire is sending open circuit to the gauge.. (or in different terms.. if the ground is wire is bad and you touch the pink to it.. it is no different than if you just pulled the pink wire off) Make sense?
The black ground wire doesn't run to the dash.. it runs from the gauge unit to the central ground bulk that all the rear lamps use. So a quick way to know if this is your problem is to run a test jumper from the ground terminal on the sender to the frame. Then check your gauge again and see what the reading is. This is why Red is asking you if you have tail lamps..
Do you have a multi-meter? If not.. I would pick one up for testing issues like these.
When you touch the pink wire to the ground wire it should give you the same reading as when you ground the pink wire out.. or empty. The ground is the problem and Red is on it.. If.. when you touch the pink wire to the ground it goes to 4... you don't have continuity.. so the pink wire is sending open circuit to the gauge.. (or in different terms.. if the ground is wire is bad and you touch the pink to it.. it is no different than if you just pulled the pink wire off) Make sense?
The black ground wire doesn't run to the dash.. it runs from the gauge unit to the central ground bulk that all the rear lamps use. So a quick way to know if this is your problem is to run a test jumper from the ground terminal on the sender to the frame. Then check your gauge again and see what the reading is. This is why Red is asking you if you have tail lamps..
Do you have a multi-meter? If not.. I would pick one up for testing issues like these.
Last edited by Willcox Corvette; Dec 3, 2012 at 12:03 AM.
Thread Starter
Instructor
Joined: Jun 2012
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I havent had chance but will get to it tomorrow.
I know when i tested continuity between the black wire and the sender unit frame i had an open circuit.
I have tail lights that are functioning.....
Are the lights and this sender ground using the same point for ground??... so am i right in thinking that there is a problem between the black wire at the sender unit and where it is grounded from the harness??
Do you know where it is usually grounded if thats the case?
I know when i tested continuity between the black wire and the sender unit frame i had an open circuit.
I have tail lights that are functioning.....
Are the lights and this sender ground using the same point for ground??... so am i right in thinking that there is a problem between the black wire at the sender unit and where it is grounded from the harness??
Do you know where it is usually grounded if thats the case?
Racer
Joined: Feb 2009
Posts: 330
Likes: 9
From: Las Vegas Nevada
Checking continuity between the black wire and the sending unit doesn't matter. That probably should be open. You need to check continuity between the black wire and the frame. If that is open or not a complete short (continuity) then that is your problem. I don't know exactly where everything grounds back there but I will no soon when I start digging into mine. The tail lights bust be grounded or they would either not work or not work properly. What you are looking for is the black wire that goes to the sender being broken or not hooked to the ground point. You can take a test wire and run it from the ground connection where the black wire is usually hooked up to the sending unit straight to the frame and if the gauge starts working properly you know for sure that that is the problem.
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
Brady.. They are on the same ground!
At this point to see if this is the problem, just run a jumper ground from the frame to the sender and you'll get your answer! If you do this and the gauge works then you know the ground is the issue.
At this point to see if this is the problem, just run a jumper ground from the frame to the sender and you'll get your answer! If you do this and the gauge works then you know the ground is the issue.
Racer
Joined: Feb 2009
Posts: 330
Likes: 9
From: Las Vegas Nevada
Thanks, I spend a lot of my time everyday at work speaking a different language "engineering". I appreciate you helping me be understandable.
Btw, I made my first order the other night. I don't think I got my discount. It was before midnight my time but after Eastern time. Your price beat the place I usually get my parts from. Been kind of thinking about switching to another source. I recently looked at how much I had spent with (that other vendor) over the years and the amount almost gave me a heart attack. I brought this up to them once that I should get some kind of lifetime discount for being such a loyal customer and for basically serving my country pretty much my whole life. I guess it didn't matter to them.
Btw, I made my first order the other night. I don't think I got my discount. It was before midnight my time but after Eastern time. Your price beat the place I usually get my parts from. Been kind of thinking about switching to another source. I recently looked at how much I had spent with (that other vendor) over the years and the amount almost gave me a heart attack. I brought this up to them once that I should get some kind of lifetime discount for being such a loyal customer and for basically serving my country pretty much my whole life. I guess it didn't matter to them.
Racer
Joined: Feb 2009
Posts: 330
Likes: 9
From: Las Vegas Nevada
I found the ground on mine tonight. It is a single wire connected to the very corner of the frame on the drivers side. May be kind of hard to get to with everything together. I have my rear bumper off so mine is easy. My ground connection was not a perfect ground.
I removed the wire and the tail lights went out. To make sure that this was also the ground for the sending unit I unplugged the sending unit and did a ohm check between the ground wire and the black wire going to the sending unit and I had continuity.
I removed the wire and the tail lights went out. To make sure that this was also the ground for the sending unit I unplugged the sending unit and did a ohm check between the ground wire and the black wire going to the sending unit and I had continuity.