I'm stumped - fuel gauge issue

[lca'73]

OK, so here's the deal. My fuel gauge has never worked properly, but for different reasons that I thought I had fixed. Now we have put the truck back together and checked all the wiring, checked the gauge, the sending unit and grounds and it still isn't working. Here's what's happening.

We bench tested the sending unit with the gauge attached and they both worked and synced correctly, all the way empty to all the way full, the needle moving with no problem as the float was manipulated. Put it on the truck. My painter/body guy put just enough gas in it to get it on and off the tow truck to get the exhaust put on and then we took it home.

Got it home, ran it and realized the gauge was on E, but figured it was because there was not enough fuel to register. Put 5 gal in it, still nothing. Crawled under and tested the sending unit, read 46, which was pretty much right on since we had already driven it around the neighborhood a few times. Took the ground off to see if it would ping past full and it didn't affect the gauge at all. Curious if the ground in the gauge has something to do with that or if the tank itself is also somewhat grounded, preventing my little test from working.

When you start the truck you can see the needle rise from it's resting position to "E", but it doesn't rise above that. So it is getting some kind of info and is not pegged past "E" and does go back to it's resting position when the truck is turned off. It moves at the same smooth/slow speed as the rest of the gauges.

Also, another concern and question that is gas related...has your sending unit ever gotten loose after driving and started leaking gas?? As we were checking the sending unit and moving a gas line, the tank started pouring gas around the sending unit because it had gotten very loose and we know with certainty that it was tight when we put it in. Is this a concern?? Should I be checking this connection frequently?

That being said, after we lost some gas and tightened the sending unit again we checked the reading and it did go up to 51, so it is reading correctly. There are no problems with the sending unit or float. There were no problems with the bench test and it does seem to be getting some kind of info...just not enough to make it correct.

Help!

Also, I only have one tank and it is a 12 gal. so no issues with switches either.

Thanks in advance!! This one has gotten tricky.

 

[akafrankcastle]

That little rubber o-ring under the sending unit can get a little wonky when you seal everything back up. That's usually the cause of leaks back there. If you're certain it's on straight, and have done a test fill with only a few gallons of gas with no leaks, make sure your lock ring is set and you should be good.

As to the electrical issues, I can't help you there. My gauge goes in and out with the weather and, unfortunately, it's fairly low on my priority list to fix.

 

[broncorick]

Electrical wiring is a pain. If you have enough wire, bypass harness and if harness is culprit 50 yr old wiring and connectors with low voltage starts to be problematic

 

[lca'73]

That little rubber o-ring under the sending unit can get a little wonky when you seal everything back up. That's usually the cause of leaks back there. If you're certain it's on straight, and have done a test fill with only a few gallons of gas with no leaks, make sure your lock ring is set and you should be good.

Tell me about it. That o-ring can be a royal pain. I guess what worried me is that we had no problems with leaks these last few weeks and then all of the sudden it just spewed. The lock ring is good and tight now, so I'll keep an eye on it. Thanks!

Electrical wiring is a pain. If you have enough wire, bypass harness and if harness is culprit 50 yr old wiring and connectors with low voltage starts to be problematic

Sadly it's not old wiring. New harness. And yes, it is a pain. I'll try bypassing it anyway. Can't hurt. Just because it's new doesn't mean anything, I've learned that lesson many times over this build.

 

[akafrankcastle]

Tell me about it. That o-ring can be a royal pain.

I like to hit the o-ring with a light shot of spray glue and stick it to the sender. Gives it enough adhesion to keep it in place while setting the lock ring.

 

[lca'73]

I like to hit the o-ring with a light shot of spray glue and stick it to the sender.

That's funny, cuz I like to put it in a sling shot and stick it to the ceiling! ;D%);D

 

[Viperwolf1]

Disconnecting the sender ground will not cause the gauge to deflect towards max (full). You want to create more current flow through the sender to deflect the gauge. Grounding the sender wire will create more current but it also bypasses the sender.
You have excess resistance in the sender wire or sender ground.

 

[blubuckaroo]

I wonder if the float actually floats?

 

[lca'73]

You have excess resistance in the sender wire or sender ground.

Ok, so then if me removing the ground had no effect on the gauge whatsoever, then clearly the issue would be in the sender wire. I'll try bypassing and see what happens.

I wonder if the float actually floats?

Yes, it seems to work fine. When I read directly from the sender in the tank I get a correct reading.

 

[clarkaw1]

I wonder if the float actually floats?

Ditto. Are you sure the float is air tight.

 

[Action]

Tank switch

On mine sometimes I have to wiggle the tank selector switch on the dash and it will work. Just throwing it out there.
Jack

 

[lca'73]

Ditto. Are you sure the float is air tight.

Maybe I'm missing something here...would I still get a correct read at the tank with a bad float? Hooked to the gauge it's incorrect, but if I read directly at the sending unit the reading is correct which leads me to believe the actual sending unit is fine and the float is working properly, but since it keeps getting mentioned, I feel like I'm missing something. This is a new and frustrating problem, so I certainly wouldn't be surprised if I've over thought it and totally missed the obvious. ;D

On mine sometimes I have to wiggle the tank selector switch on the dash and it will work. Just throwing it out there.
Jack

Thanks Jack, but I don't have two tanks, just the one, so no switch to argue with.

 

[garberz]

Maybe I'm missing something here...would I still get a correct read at the tank with a bad float? Hooked to the gauge it's incorrect, but if I read directly at the sending unit the reading is correct which leads me to believe the actual sending unit is fine and the float is working properly, but since it keeps getting mentioned, I feel like I'm missing something. This is a new and frustrating problem, so I certainly wouldn't be surprised if I've over thought it and totally missed the obvious. ;D

If you're getting correct Ohm readings at the sender, like you mentioned, then I think you can rule out the sender as a problem. Mine was the gauge itself. If I grounded the gauge, it would run the entire sweep, but applying varying resistance, it had a huge dead spot. I replaced the gauge with an oil pressure gauge, (just changed the face plate) and it's been working fine. The fuel, oil and water temp all use the same Ohm range, just the faces are different.

Mark

 

[lca'73]

If you're getting correct Ohm readings at the sender, like you mentioned, then I think you can rule out the sender as a problem. Mine was the gauge itself. If I grounded the gauge, it would run the entire sweep, but applying varying resistance, it had a huge dead spot. I replaced the gauge with an oil pressure gauge, (just changed the face plate) and it's been working fine. The fuel, oil and water temp all use the same Ohm range, just the faces are different.

Mark

That's a huge help, Mark! Thank you!!

 

[Viperwolf1]

There is one connector in the sender wire under the hood. It's a square 4-pin connector on the driver side of the firewall. It has the orange wire in it. You could ohm test both sides to see where the problem is. My guess is the wire is damaged along the frame.