1974 Fuel Gauge

[Raymond W.]

I've recently purchased an original equipment reproduction fuel gauge from GM Restoration Parts. The replacement of my current fuel gauge was for cosmetic reasons only.

With the ignition on, the needle moves outside of the (E.....F) readings. When it stops, it's pointing at 4 o'clock. When the ignition is turned off, the needle remains in the same position. I've yet to start the car from it's 5 month winter storage.

I reinstalled the old gauge, turned on the ignition, and the needle moves to the Full mark.

Is the new gauge faulty? Do they require calibration? I would appreciate any other thoughts from those more familar with instrument gauges.

Thanks,
Ray Wells

[Jim K.]

Re: 1974 Fuel Gauge

I have a 71 and it does the exact same thing. So I am waiting for an answer to this also. The good thing is that when it drops below a certain point it reads correctly. Jim

[Jack H.]

Re: 1974 Fuel Gauge

Starting the car won't have appreciable effect except to 'peg' the gas gauge further. Circuit in '68 and later cars is identical to '62 and prior cars, only the mid-year cars had a unique fuel gauge system based on Whetstone bridge circuit topology. Here, the system is straight forward....

B+ is fed to gas gauge at the dash based on ignition switch. Wire out of gauge runs to the tank sender which is a rheostat to ground. Position of swing arm in the tank dictates how much resistance is in series with the gas gauge and dictates the position of the pointer needle.

If the gauge is reading full or beyond full when the ignition is turned on and the tank isn't full, the gauge isn't 'seeing' a correct sender resistance due to (1) shorted wiring or (2) fault ground.

[Joe L.]

Re: 1974 Fuel Gauge

Ray------

Assuming that the gauges, new and old, are being installed in an identical manner (wiring, grounding, etc.), I would have to say that there is some problem with the new gauge. The fact that the original gauge seems to work perfectly would seem to me to rule out any possibility of problems with other parts of the system.

I know of no need to calibrate or otherwise adjust the new gauge.

[Raymond W.]

Re: 1974 Fuel Gauge

In my case, the gauge is reading beyond full when the ignition is turned on and the tank is actually full. The old gauge provided a more accurate reading, while the new gauge is overstating the "full" status of the tank. The old gauge and the new gauge are under the same ground effects which makes me confused as to why the old one works, the new one doesn't? Is there a problem with the new gauge? Tests?

[Joe L.]

Addendum

Ray-----

Also, starting the car should have nothing to do with the operation of the fuel gauge. With the ignition in the "on" position, it should work as good as it's going to work. Starting the car is necessary to check full operation of the ammeter, temperature and oil pressure gauges, but it's got nothing to do with the fuel gauge.

[Raymond W.]

Re: Problem Solved

Traveled down to Dr. Rebuild today and picked up a '74 NOS Fuel Gauge. This gauge is registering the correct "Full Tank" gas measurement with the needle resting sligtly right of the line. The OER from GM Reproductions had to be faulty. Thank you Dr. Rebuild and to all others who offered me their assistance.