Fuel Gauge Problems, need some help

[Sterling]

Hello guys,

I have dual gas tanks. Here is my situation

Full to the rim, the Right hand tank when selected reads just at about HALF tank. Then it reads going down from there. Reads about the dash after empty at half tank, and really doenst go down farther from there, Ive gone to about 16/20 gallons used, but I dont dare go further to run risk of running a diesel dry.

Now the left tank (drivers side) reads about a half inch past the Full line , but doesnt move at all


I have a feeling the left tank has a ground issue with the sender, and I feel the sender or float is bad on the right.

Am I close? or has someone experienced this before and knows better?

I want to tackle 1 tank at a time, I can atleast drive it with one tank off. But want to have parts ready

-Sterling

[motornut]

over full sender off
E short
inbetween ...ground
I'd work over the switch/grounds

[hatzie]

This assumes this is the 1982 truck you've posted about... 1973-1980 are different.

It's probably the senders but...

Test the gauge first. It's easy to test and easy to change.
You'll need

1. A multi-meter.
2. A Radio Shack 100 ohm volume control potentiometer
3. Alligator clip test leads.
4. Several Male Delphi WeatherPak terminals. The connecting wire gauge doesn't matter these are to hook test leads to WeatherPak plug sockets without damaging them ( I keep a handful of mating connector pins in 40 mil plastic baggies for various connector families in my meter bag ). Delphi Male WeatherPak Terminal #12124582, 12089040, or 12089307

Follow these instructions from the Corvette guys to build a cheap Potentiometer fuel gauge tester... Note: Our 73-91 gauges are 0-90ohms like the C3 not 0-30ohms like the C1.
http://www.lbfun.com/warehouse/tech_...lGaugeTech.pdf

1. Clip the leads from your fuel gauge tester to your multi-meter and set the POT to 45 ohms.
2. Unplug the tank selector valve on the RH frame rail.
3. Insert one male terminal in socket B of the wiring harness plug you just removed from the valve.
4. Turn on the ignition. The fuel gauge should be pinned at 3:00 or close to it.
5. Clip a test lead from a frame ground to the terminal in socket B. (this wire goes to the sender terminal on the gauge). The gauge should go to E.
6. Unplug the ground from terminal B and sub one leg of your tester. Clip the other leg of the tester to the frame ground. The gauge should read @ 1/2 tank.
7. Set the POT to 90 ohms and re-install on the valve plug as before. This will set the needle at F.
8. 29 ohms is 1/4 and 64 ohms is 3/4....

If the gauge reads wonky check the wire from the firewall bulkhead plug under the brake booster to the valve plug for damage. Replace the gauge if the wire checks out.

You can check the senders at Full without removing a tank as follows.

1. Fill the fuel tanks.
2. Pins A & C of the tank valve plug are from the senders... insert Male weatherpak test pins in socket A and C.
3. Attach one meter lead to the frame ground used in the gauge test and attach the other meter lead to pin A or C.
4. Check each sender resistance with your meter set on 1K scale. It should be @ 90 ohms.
5. If a sender reads open or too high check that tanks' frame to sender ground.
6. If the sender reads too low then it's probably just bad.

[Sterling]

Thanks Hatzie, Ill drive my truck over to our heated warehouse (its around 0 F outside) and give those tests a try. Updates to follow