Gas Gage Stuck on Full

34_chevy · February 8, 2007

New to the forum but what I've seen looks great. Anyway, I have a 1997 GMC 7.4 lt 1-ton crew cab dually. Last week I noticed the gas gage had pegged out way over past full and doesn't move at all with key on or off. Any suggestions what could be wrong and how to fix? I would appreciate it.

MikeDirntRulez · February 9, 2007

Here's a simple thing you can try....

I'm not sure who sells it but you can find out who does just by walking to where the fuel injector cleaners are in your auto parts store... There should be a product with a label on it saying "Gas Gauge Stuck?". I think Valvoline might make it.

Pick this stuff up and go fill up your tank FULL, fuller than you have ever filled it before (but dont overfill). While it is full, dump that cleaner in the tank. You probably will need 2 bottles, maybe even 3.

Drive around and see if it helps it any. If you notice that it moves a TINY bit, keep repeating this process until the floater in the tank is free and your gas gauge works.

If this does not work, then you need to drive around until all of your fuel is empty. COMPLETELY empty, to where your truck wont run anymore. That's when you need to drop the tank and possibly replace the sending unit, or free it if it is binding. If you empty the tank completely, you shouldn't have to wrestle with it too bad, and it should take you less than a couple of hours.

If you do decide to drop the tank, it would be a VERY good time to replace the fuel pump in the truck. GM fuel pumps are known for going at the worst time, so get it out of the way while you have the tank down. Trust me, you will WANT to replace the pump if you pull the tank.

Hope this helps some, let me know if you need any clarification or have any questions.

34_chevy · February 9, 2007

Here's a simple thing you can try....

I'm not sure who sells it but you can find out who does just by walking to where the fuel injector cleaners are in your auto parts store... There should be a product with a label on it saying "Gas Gauge Stuck?". I think Valvoline might make it.

Pick this stuff up and go fill up your tank FULL, fuller than you have ever filled it before (but dont overfill). While it is full, dump that cleaner in the tank. You probably will need 2 bottles, maybe even 3.

Drive around and see if it helps it any. If you notice that it moves a TINY bit, keep repeating this process until the floater in the tank is free and your gas gauge works.

If this does not work, then you need to drive around until all of your fuel is empty. COMPLETELY empty, to where your truck wont run anymore. That's when you need to drop the tank and possibly replace the sending unit, or free it if it is binding. If you empty the tank completely, you shouldn't have to wrestle with it too bad, and it should take you less than a couple of hours.

If you do decide to drop the tank, it would be a VERY good time to replace the fuel pump in the truck. GM fuel pumps are known for going at the worst time, so get it out of the way while you have the tank down. Trust me, you will WANT to replace the pump if you pull the tank.

Hope this helps some, let me know if you need any clarification or have any questions.

34_chevy · February 9, 2007

I appreciate the information. I will try the cleaner first. I'll probaly wait till it gets a little warmer before tackling the other if this doesn't work.

Thanks again,

mmmikkke · February 9, 2007

If it's stuck way-past-full, it's probably an electrical problem in your dash, and I'd hold off on using the cleaner...your truck is not that old.

Are any other gages misbehaving? If so you might have just lost an electrical ground. Look around under the carpet, near the firewall, for places where the wiring harness sends out a ground. Look for black wires which are screwed to the firewall. Also check behind the driver's side kick panel. See if any corrosion is present, or if the connection is loose. After messing around with this, check to see if the gage is now working properly. Sometimes it only takes being disturbed and then it will work fine again.

Being stuck way-past-full is the dead giveaway. If your gage never went that far up before, it's not a problem with the sending unit.

34_chevy · February 9, 2007

This is the only gage that is not working. I'll try looking for a ground. I had a guy today tell me to try this -

Unplug the harness from the tank. There should be 3 wires in the harness. Locate the wire that goes to the sending unit (usually purple, but check to make sure the wire doesn't have 12v + power with the key on). Once you have the wire to the sending unit, ground it and the gauge should go to full...If it does, then the wiring and the gauge are OK, problem's in the sending unit... Since youre gauge is alreay reading full, unplug harness and see if it goes to empty; if it does, then the sender is shorting to ground...

I'm going to try your suggestion first.

Thanks,