67-72 Chevy Truck fuel gauge diagnostics 101

[jjzepplin]

Originally Posted by jjzepplin

So I went and filled it up today. Bad news. Reads just over 1/4 tank. More than before but dagnabit! And as an added bonus now it burps gas upon fillup again for some stupid reason. SHAZAM! On the other hand the new front sway bar makes it ride fantastic. Think a rear is on the way.
I did not do any testing yet but will keep you all posted.

Allrigty. Went out and tested the sender today to find it is reading 90 ohms-hmm. Went inside the cab and pull the sender wire and it reads 90 ohms- hmm. Pulled what I thought was the ground clip for the gauges and nothing happened to the gauge.
Is there more than one ground clip?
This gauge and sender tested fine out of the tank. Why would it be any different inside the tank?
The only difference I can find is the tank sender ground was a jumper wire.
I have a ground wire on the tank that previously was not hooked up but it is now.
Sound like a ground issue?

[TBONE1964]

Originally Posted by jjzepplin

Allrigty. Went out and tested the sender today to find it is reading 90 ohms-hmm. Went inside the cab and pull the sender wire and it reads 90 ohms- hmm. Pulled what I thought was the ground clip for the gauges and nothing happened to the gauge.
Is there more than one ground clip?
This gauge and sender tested fine out of the tank. Why would it be any different inside the tank?
The only difference I can find is the tank sender ground was a jumper wire.
I have a ground wire on the tank that previously was not hooked up but it is now.
Sound like a ground issue?

JJ,

The tank is full? If you are reading 90 ohms testing the sender, that would tell me the tank is full and the float is up all the way. If you were reading 22.5 ohms, then I would say the float is stuck at 1/4 tank or the sender is not working correctly

The little ground clip for the cluster is just an extra ground as a back up. The ground for the cluster is in the connector I believe with out looking it up is in the number 7 location. It is a black wire.

If you have a ground issue at the cluster, the temp gauge and/or lights would not work correctly. They all share a common ground.

What will happen now if you hook your jumper ground back up? Try it and see what happens. Are you still reading 1/4 tank? That would indicate to me that your ground is good. If you pull ground, the gauge should roll over to 3 o clock.

Keep us posted and have a good holiday,
Tom

[jjzepplin]

The tank is indeed full.
The ground clip removed does not change the gauge reading.
Maybe pull the big cluster plug and jiggle around?
I am going to try the jumper wire at the tank.
Is that what you mean?
I tried the ground clip to a known ground and nothing.

[TBONE1964]

Originally Posted by jjzepplin

The tank is indeed full.
The ground clip removed does not change the gauge reading.
Maybe pull the big cluster plug and jiggle around?
I am going to try the jumper wire at the tank.
Is that what you mean?
I tried the ground clip to a known ground and nothing.

Are you talking about the ground clip near the cluster? It is always good to have it hooked up but I don't think it is related to your problem.

Yes, the jumper ground at the tank but like I said, If you have a bad ground there, that will make the gauge read past full.

It sounds like you have confirmed the sender is good and the test worked.

Do you have another loose fuel gauge with the resistor on it? If you do, try to give it 12v and a ground and unplug the tan wire from the fuse panel and hook it directly to your other gauge and see what that gauge does. This is going to tell you if the gauge resistor is keeping the gauge from reading past 1/4 tank. Let me know if you need help figuring out where to hook the jumpers on the back of the gauge.

I know this is a PITA but think you have/had multiple problems with your fuel gauge not reading correctly.