Fuel Gauge Issue

[Clarkie]

Hi all. My 1985 Sierra Classic that I own again after selling it 11 years ago has always had a problem with the fuel gauge, even when I first bought it 30 years ago. The gauge works properly on occasion, but most of the time it read well past full.

I ran it out of fuel literally about a half-mile from home. The truck came with a new fuel sending unit when I bought it back, so I thought it would be the perfect time to change out the sending unit since I wouldn’t have to drain n the tank.

Well, once I dropped the tank, nothing appeared to be wrong visually, so I cleaned up where the sending unit bolts to the frame to ensure it was getting a good ground, bolted the ground wire of the new sending unit to the frame, plugged the power wire to the sending unit, turned the ignition key to the run position, and moved the float of the sending unit up and down while I watched the needle on the gauge. No movement of the needle at all.

Next, I left the ignition in the run position, and tested to see if there was 12 bolts at the power wire by putting the positive probe in the power wire connector and holding the negative probe to the frame of the truck. It would read anywhere from 0 to about 6.5 volts with each of the many attempts to get a reading.

I then looked up under the dash to see if I could see anything amiss, but I couldn’t really find anything.

The fact that it used to work intermittently, tells me that sometimes it was getting good power or good ground (or both) on occasion.

I don’t know what my next step is. Any suggestions?

 

[Dmack]

You can test the sender with an ohm meter. Pos to.the stud in the sender, neg to the body. Moving the float arm should give you a varying reading, I think from 0-90.

If the sender is working, I would try replacing the wires. Gauge reading at 3 o'clock means an open circuit. 9 o'clock means grounded out.