Gas guage Q's

[xfsketch]

72 chevy 350 4 blt main

Hey guys I have been experiencing some major gremlins in my electrical wiring all over this truck. The truck sat for a while & the PO unhooked everything. So far the oil pressure guage and the speedometer are all I have working. I pulled the dash cluster and sprayed the wire harness with some electrical cleaner and did the same for all the connections from front to rear, even on the firewall. I will post the other issues I have in a seperate topic. RIght now I need help with my gas guage. I read online that the stock tank on my ride is 20 gallons. Yesterday I put $35 in the truck right after it ran completely out of gas and the guage only read 1/4 a tank. YES gas prices are very high and I only put 11.5 gallons in it. My questions are as follows.

1. Is there a reserve amount of gas so when your on E you still have a few gallons left in the tank? Because I should have a half a tank but it only reads 1/4.

2. Could it be a ground issue? If so where is it located?

Any help is appreciated. Ive read most of the posts on gas guage probs and havent found one that has the same thing goin on.

[49studebaker]

My first thought is that possibly the float is water logged. I've seen them fill up with gas (ok, gas logged), which of course makes them heavier. If you were to take the sending unit out of your tank and manually move the float from top to bottom you will know if that's the problem by watching your gauge. It'll need to be grounded while you do this. Or remove the float and you can tell by shaking it. Also, if you have an ohm meter, it should read 0 ohm's and go to 90 ohm's as you lift the float. If it registers at all, my guess is that your wiring is fine. Hope this helps.

[xfsketch]

Thank you 49... I will try this tonight if I get a chance. I think you may be right because why would it work at all if the ground was bad it wouldnt read anything. I will post my results tomorrow on this thread. Thank you for your quick reply!

[Longhorn Man]

Personally, I would just top it off and see what it does. I've never seen two trucks work the same when it comes to the fuel guage. That may just be a quirk to your truck.

[cdowns]

these gas gauges are just rough estimates no scientific accuracy// best way to tell how long your truck will run on empty is to have a 2gallon can of gas with you and run around town on empty when the truck starts sputtering and stalling you've got your answer

[Longhorn Man]

well...2 gallons, if you know you'll run out within a few blocks of the gas station.
I actually ran out of gas, walked to the gas station, got a 1 gallon can, and walked back...drove 1/2 way to the gas station, and had to walk there again with the can for another gallon.
For the record, that was with a jacked up carb, and the engine was cold, and sat for a week and some one drained the entire tank when i wasn't looking.

[xfsketch]

Originally Posted by 49studebaker

If you were to take the sending unit out of your tank and manually move the float from top to bottom you will know if that's the problem by watching your gauge. It'll need to be grounded while you do this.

I took the sending unit out and heres what it looked like. I checked the float for holes (none that I could tell). I see a gas line where it looks like it stays. While I had it out I hooked the wire back up to it and held the float up the guage went to full, but it stuck there. No matter which way I moved it there was no change. Once I put it back in the tank it read 1/4 again. What do you guys think?

[Woelf90]

You said that you clean the wires in the dash, do all the other gauges still work? The reason I ask is that I have 77 and I replaced my oil pressure, temp, and amp gauge and now my fuel gauge doesn't work anymore. What I have since found out is that the other gauges (i.e. the ones that are now gone) have resistors on them that brings the amps down for the fuel gauge.
Speaking of which, does anyone know where I can get an aftermarket fuel gauge that is straight wired to the sending unit?

[VetteVet]

http://www.6066gmcguy.org/Electrical-02.htm

[xfsketch]

Originally Posted by Woelf90

You said that you clean the wires in the dash, do all the other gauges still work?

I took the guage cluster out but didnt unhook anything but the wire harness that comes from behind the gas guage. I assume this is the wiring harness for all the guages except the speedo and oil pressure.
I just found out yesterday that my temp guage isnt hooked to the engine block so thats why that one dont work.
Thank you

[xfsketch]

Originally Posted by VetteVet

http://www.6066gmcguy.org/Electrical-02.htm

Thats a nice link for troubleshooting the gas guage. Thank you!

[VetteVet]

You're welcome. It's good to see that someone actually looked.