Fuel Guage Gremlin

[ekgguy]

I have a 68 with idiot lights that is giving me problems. The fuel gauge reads E all the time except when the truck is off and has been sitting.

Here is the scenario:

No matter how much gas in in the tank, when the truck is running, it reads E. When the truck has been sitting for a while the gas gauge will start to creep up. The longer it sits, the higher it goes until it reaches approx. 1/2 and then stops. I have never seen it higher then that.

I have the entire interior out of the truck so tracing wires is easy. today I traced the ground wire to the fuse block and pulled the plug. Turned the key on and the gauge went way past the F mark, to about 4pm. Turned the key off and it stayed there. Plugged the wire back in and turned the key on, the needle went back to E.

It goes without saying how much I do not know about the electrical workings of vehicles.

Thanks in advance.

[VetteVet]

When you pull the ground wire off at the fuse block you should get the reading that you did.
When you ground the wire at the fuse block you should get a completely empty reading.Which is what you are seeing/ Logic says that the wire to the fuse block is grounding someplace between the fuse block and the sending unit. For accuracy the ground wire is called the sending unit wire.
Here's what you need to do first. If you have a multimeter.Take the sending unit wire off at the sending unit and at the fuse block and check for continuity between the wire and the truck at a good ground point. You should read a very high resistance near infinity. If you get near zero ohms then your wire is shorted to the truck sheet metal and one of the most common places is under the drivers sill plate where the wire runs to get back behind the seat to the fuel tank sending unit.

A quick way to test the wire is to unplug the sending unit and the fuse block and just run a wire straight from the fuse block to the sending unit terminal. Then turn the key on and you should get a reading that conforms to what is in the tank.

If the wire checks out good then your sending unit might be bad and possible the float has a pinhole in it and it has filled with gas. That would result in an empty reading because the float would be heavy and perhaps not rise with the fuel level.I would speculate that the float should rise somewhat and give an inaccurate reading even if it was full of gas.

[ekgguy]

I have tested the continuity of the wire between the tank and the fuse block and it showed 2ohms, so I replaced the wire with the same result. When the truck is on and running the gas gauge shows empty. After sitting for a while the gauge starts to creep up.

[VetteVet]

Take the wire off at the sending unit and you should get the 3:00 reading with the key on.
If you do, then take the sending unit out and reconnect the sending unit wire and ground the sending unit mounting flange on a good cab ground. Turn the key on and move the float up and down and watch the fuel gauge for movement. It should cycle from empty to full as you move the float arm. Another check to do is connect the ohm meter between the center terminal on the sending unit flange and the mounting flange and move the arm. You should read between 0 and 90 ohms with the sending unit out of the tank and no wires hooked to it.

[ekgguy]

Thanks. I will try that when I have my next few days off.

[camarodude87]

Anything????

[ekgguy]

Haven't had any time to work on the fuel gauge issue. Been working a lot lately and driving the wife's car.

I am off four of the next six days so hopefully I will get some time with it. It really sux having it sit in the driveway. I would much rather be driving it instead of a BUICK.

[SideStepper]

I don't mean to Hi-Jack this discussion,
but I have a similar problem on my 96 Chevy PU. While driving the gas gauge pegs from full, to empty & back to full again...constantly every minute & never levels out. All though the sending unit is only 4 years old, I think the signal is bad to the fuel gauge. I want to determine where the problem is. If I pull out the sending unit & move the float up & down, should I get the same 0-90 ohms on a 96 Chevy just like the older years?

[VetteVet]

Originally Posted by SideStepper

I don't mean to Hi-Jack this discussion,
but I have a similar problem on my 96 Chevy PU. While driving the gas gauge pegs from full, to empty & back to full again...constantly every minute & never levels out. All though the sending unit is only 4 years old, I think the signal is bad to the fuel gauge. I want to determine where the problem is. If I pull out the sending unit & move the float up & down, should I get the same 0-90 ohms on a 96 Chevy just like the older years?

You should get the same 0 to 90 ohms if you have the sending unit grounded which I think may be your problem.

[ekgguy]

Update:

Bought a 69-73 Camaro tank and sending unit to go under the bed. Gauge works perfect.

When we took the old tank out, the old sending unit was kaput.

[VetteVet]

::

Originally Posted by ekgguy

Update:

Bought a 69-73 Camaro tank and sending unit to go under the bed. Gauge works perfect.

When we took the old tank out, the old sending unit was kaput.

Thanks for the feedbackl