My Corvette is fuel gauge challenged?

[Michael G.]

Good evening Corvetters,

My 1963 Corvette is currently fuel gauge challenged. I recently filled my tank full for the 1st time after 2+ year restoration. I observed the fuel gauge registered only 3/4's of a tank. The sender unit was replaced during the restoration and original harness is still being used. I've since removed the sender from tank, reconnected the wires and checked range of motion of the float. Nothing changed at gauge. All lights at rear appear to be working properly which use the same ground as sending unit as I understand. Any thoughts here would be appreciated. Thanks in advance.

Mike
#28614

[David K.]

Re: My Corvette is fuel gauge challenged?

My '67 does the same thing. (or something similar, I think)
Mine goes from full to 3/4 full, as the float moves from full to empty.
I hooked my gauge up in a buddy's '67, (with known working fuel gauge), and it worked fine. I hooked a known good gauge up to my wires, and it didn't work either.
I'm not certain, but I believe I wired a gauge straight to the sending unit on the tank, (not going through the wiring harness) and got the same results.
I measured the resistance at the sending unit as the float moves up and down, and found it to be wrong. (I beleive the SM has the correct resistance values)
I checked the wiring/grounds from front to back, and have concluded it is the sending unit.
I have yet to replace it. Wish I had when I had the tank out, but I didn't know it was broke then.
I would be interested if you found your problem to be something different.

[David K.]

Re: My Corvette is fuel gauge challenged?

My '67 does the same thing. (or something similar, I think)
Mine goes from full to 3/4 full, as the float moves from full to empty.
I hooked my gauge up in a buddy's '67, (with known working fuel gauge), and it worked fine. I hooked a known good gauge up to my wires, and it didn't work either.
I'm not certain, but I believe I wired a gauge straight to the sending unit on the tank, (not going through the wiring harness) and got the same results.
I measured the resistance at the sending unit as the float moves up and down, and found it to be wrong. (I beleive the SM has the correct resistance values)
I checked the wiring/grounds from front to back, and have concluded it is the sending unit.
I have yet to replace it. Wish I had when I had the tank out, but I didn't know it was broke then.
I would be interested if you found your problem to be something different.

[Jack H.]

Re: My Corvette is fuel gauge challenged?

The fuel gauge system used in mid-year cars is unique as it's based on a Whetstone bridge circuit topology. All that boils down to making the gauge INDEPENDENT of absolute battery voltage and branch circuit current flow.

Since this was a departure from how earlier gas gauge systems functioned (AND different from how later, Shark era, systems worked), the Corvette Shop manual (and Chassis Service Manual for '66 and '67 cars) specifically addressed the situation by giving the service technician a schematic diagram AND a troubleshooting table listing gauge symptom vs. what to look for as a problem source.

That's where you ought to start in troubleshooting your car, vs. hit & miss.... Don't have this info in your support library for 'baby'? Shoot me an email and I'll reply with an attached file containing the info....

[Jack H.]

Re: My Corvette is fuel gauge challenged?

The fuel gauge system used in mid-year cars is unique as it's based on a Whetstone bridge circuit topology. All that boils down to making the gauge INDEPENDENT of absolute battery voltage and branch circuit current flow.

Since this was a departure from how earlier gas gauge systems functioned (AND different from how later, Shark era, systems worked), the Corvette Shop manual (and Chassis Service Manual for '66 and '67 cars) specifically addressed the situation by giving the service technician a schematic diagram AND a troubleshooting table listing gauge symptom vs. what to look for as a problem source.

That's where you ought to start in troubleshooting your car, vs. hit & miss.... Don't have this info in your support library for 'baby'? Shoot me an email and I'll reply with an attached file containing the info....

[Gerard F.]

Re: My Corvette is fuel gauge challenged?

Mike, David,

Review the following post from the archives, and try the resistence test on the sender contained within.

https://www.ncrs.org/forum/archive18.cgi?review=151025

The test was for a 67 although I think a 63 is the same. You will at least know whether it's the sender or something else.

There is also lots of other posts further back on the subject.

Jerry Fuccillo
#42179

[Gerard F.]

Re: My Corvette is fuel gauge challenged?

Mike, David,

Review the following post from the archives, and try the resistence test on the sender contained within.

https://www.ncrs.org/forum/archive18.cgi?review=151025

The test was for a 67 although I think a 63 is the same. You will at least know whether it's the sender or something else.

There is also lots of other posts further back on the subject.

Jerry Fuccillo
#42179