fuel gauge

[dooguy]

fuel gauge on 72 k20 not working. ok when parked in fall. where to start. all other gauges appear ok

Thanks

[A1971Blazer]

https://67-72chevytrucks.com/vboard/...d.php?t=640615

[54blackhornet]

I had an inoperative fuel gauge. I replaced the sending unit, rechecked all the continuity. Eventually I determined that the needle was just stuck in place. Had the cluster out and just moved it a bit with my finger. Original gauge still works fine. Can’t say that about a lot of the new Chinese knockoffs.

[oneshotkyle]

Take the sending unit wire of sender, ground it out. If gauge moves its the sender. This was my problem ha

[dooguy]

thanks for replies. got some work to do. i have a relocated tank under bed and it may be a process to get to wire

[pjmoreland]

Originally Posted by dooguy

thanks for replies. got some work to do. i have a relocated tank under bed and it may be a process to get to wire

Initially you could just access the tan sender wire where it plugs into the fuse panel under the dash. Unplug it there and ground the fuse panel Fuel Gauge terminal to see if the gauge moves to Empty.

[old51sedan]

Originally Posted by dooguy

thanks for replies. got some work to do. i have a relocated tank under bed and it may be a process to get to wire

I put a new suburban tank under the back of my truck 3 years ago, last summer after final assembly I got the truck out and was on empty all the time. Pulled the sending unit out and the float was full of gas. Bought a new plastic float for a jeep as recommended by folks here, solved my problem.

[dooguy]

Originally Posted by A1971Blazer

https://67-72chevytrucks.com/vboard/...d.php?t=640615

thanks for link

[1970cstblazer]

Make sure the tank is grounded to the chassis.

[pjmoreland]

It should be a tan wire that plugs in at the end of the fuse panel.

[dooguy]

thanks for the picture locate, I will check it out

[dooguy]

the gauge is registering E now. when grounding out would gauge peg hard to left (empty side)

[pjmoreland]

Disconnecting the tan wire from the fuse panel with the ignition on should cause the needle to move way past Full to around the 3 o'clock position. Then grounding the fuse panel terminal should move the needle back to Empty. If it acts that way, then your gauge is likely good.

[dooguy]

gauge cks good. thanks for the pic.
guess i need to make sure wire from fuse panel to tank is good. tank and sender not very old. I'm hearing alot of parts we are getting are from China and not good quality

[oneshotkyle]

Originally Posted by dooguy

gauge cks good. thanks for the pic.
guess i need to make sure wire from fuse panel to tank is good. tank and sender not very old. I'm hearing alot of parts we are getting are from China and not good quality

Run a cheap piece of wire to sender to try or just take the 2 minutes and remove the sender to test

[dooguy]

Originally Posted by oneshotkyle

Run a cheap piece of wire to sender to try or just take the 2 minutes and remove the sender to test

looks like wire from fuse pnl to sender is good. it would be a quick job to remove sender if it wasn't located on top of fuel tank and pu bed sitting over the relocated fuel tank was removed

[71CHEVYSHORTBED402]

Originally Posted by pjmoreland

Disconnecting the tan wire from the fuse panel with the ignition on should cause the needle to move way past Full to around the 3 o'clock position. Then grounding the fuse panel terminal should move the needle back to Empty. If it acts that way, then your gauge is likely good.

Good stuff Moreland.

[pjmoreland]

Since the gauge returns to Empty when you have the sender wire connected, that tells me the sender wire is providing a path to ground. Your tank is likely adequately grounded. My guess, as others have already mentioned, is that your sender float has filled with gas and has sunk to the bottom of the tank.

[PbFut]

Grounding the wire at or just in front of sender would have eliminated a few steps. I agree. You have a bad sender. Either a result of a faulty float or potentiometer in the sender. Either requires pulling the sender to verify. You can put a ohm meter on the sender. Swinging the float arm should move your meter from 0 to 90 ohms.

[RustyPile]

Six years ago when I bought my '71, the fuel gauge did not work.. The brass float had rotted out and sunk to the bottom. I installed an LMC sending unit and the gauge worked perfectly. 3 - 4 months later, the gauge quit working again. The solder joint on the float had failed, the float filled with gas and subsequently sunk. LMC provided me with a replacement sending unit. A few weeks later it failed. I returned the sending unit and LMC issued a refund. I bought a sending unit from Classic Industries, and examined the sending unit to see if I could determine the reason for the solder failure.. The float fitted tight in the "loop" of the arm. I removed the float and opened the loop enough that the float was loose but well captured.. This all happened in 2018.. Today that same float/sending unit is in my truck, working perfectly..

As you know, solder doesn't have much structural strength. I believe the loop fits the float too tightly, causing stress on the solder joint, and it will eventually fail. Loosen the loop , releasing that tension and the premature float failure issue is resolved.