Quick Tips - Gas Guage Operation

One of the biggest mysteries is making sure the gas guage is working properly. Nobody wants to be stranded out of gas. Knowing what's in the tank gives that sense of comfort while driving - it's a great feeling.

Here's a quick test that will put that mystery away.

This process can be applied to all cars except those with computerized gauges.

1) Ensure your gas guage as power to it. Check the fuses to be good or put a test light on the terminal (with the ignition on)to ensure power is there.

2) Locate the fuel sender feed wire near the fuel tank. You're looking for a single tan (typical colored) wire. With the tan wire disconnected at the fuel tank, the fuel gauge should read past full with the ignition on. Wait a few moments as some fuel gauges take a time to respond. Touch the tan wire from the body to any good convenient ground and the gauge should read empty. If not, you have a wiring problem or a bad gauge.

3) If the gauge responds correctly, the gauge and wiring are OK. Next use a multi-meter to measure resistance to ground of the sender wire connection on the top of the fuel sender or the "tan" wire from the top of the fuel tank. Measurements should track the fuel in tank.

(Estimated - These are GM Figures)
Just know, with the fuel gauge at empty, you get 0-2 ohms. With the guage full, you should have a reading up to or above 88 ohms.

Full - 84-88 ohms
Half - 40 ohms, give or take
Empty - 0-2 ohms

If this doesn't check, then sender or wiring on top of the tank is bad or the sender not adequately grounded. Senders are typically grounded by a black wire which is welded to the sender and attached to the body with a sheet metal screw. Also know, some senders are grounded directly to the tank itself. If sender needs a good ground; a quick fix would be to remove one screw from the sending unit, clean the surface of the sending unit; make a lead using an "O" or donut termial on each side and install proper. Make sure your ground is to good bare metal. Use a drill with a wire brush to clean your ground surfaces.

4) If the sender checks OK but gauge and wiring don't, clean the connections, reconnect the sender wiring. Again, when removed the gauge should then read past full. Ground the tan wire on the dash side and the gauge should read empty. If not, you probably have a bad gauge or possibly a dash wiring problem.

5) If the gauge checks OK, then make the same resistance checks to the "tan" wire in wire loom. If it checks bad, inspect your wiring or run a new wire to replace. Its common to have old wiring crack and ground out on the body, creating issues unseen.

In Conclusion; the gas guage must have a good ground and good wiring to operate properly. Its always good to remove your old sending unit and clean it good with electrical parts cleaner or carburator cleaner. When you have it out, make sure the float is in good shape and is 'gas' tight.

Good Luck and Motor On!