Intermittent Fuel Gauge - Electrical Issue?

[James Pope]

I have a 1971 Plymouth Satellite 318. When I bought it, it had a few small electrical things that needed to be addressed, most of which were solved by just cleaning some corroded grounding points for various lights (license plate light, for example). But there's one issue I can't seem to fix: the fuel gauge. When I purchased the car, it was dead. The temperature gauge works, so the IVR is good. Then one day, the fuel gauge randomly started working. I didn't touch the ground strap, pull the cluster, or mess with wires behind the dash. It just started working and read an accurate amount of fuel based on when I had last filled up. I thought great, no worries now. Then it stopped working after I turned off the car to get a drink, came back out and it was dead again. I suspected a bad ground at the strap at the fuel tank: took it off, cleaned it, and it worked again. Then next day it was dead once again. I tried to clean the strap again but broke it, and while waiting for a new one went for a drive - and the fuel gauge was up and running once again, without the ground strap. There seems to be no rhyme nor reason to when or how the gauge works, and I'm at a loss. Anyone with a bit more experience have any suggestions on what I should check?

 

[69a100]

Your just going to have to stay on top of it to get it figured out. My A100 did the same thing out of nowhere, fiddle farted around cleaning the fuel lines around the strap, the strap itself, etc. etc. and was working, then dead again for no reason. I did the thick wire with 2 hose clamps and removed the old strap trick and that worked for a while then died. Put in a new sender thinking it was going bad, nope, then my gauge didn't read right with the new sender. I lived with that while I did a good check out with the old sender, it's fine. Removed the new sender, cleaned the hole area for the ring, and everything else in the area again, got a new ground strap and put it all back together and crossed my fingers. All has been fine since. So make sure the round plate on the sender and it's mating surface are clean is the only thing I can think of. It's more of a nuisance then a problem to fix? The problem is you don't know where it's mucking up? Good Luck

 

[PurpleBeeper]

Yep, you've either got a loose wire or the insulation has worn off the wire going to the fuel sending unit so it sometimes gets grounded or the fuel sender is on its last leg.

Now that I think of it, what does the gage do when it isn't working? Does it go to "empty" or "full". I think there's a fuel gage test where you just ground the one wire going to the sending unit & see what the gage does. I'm not sure, but that might give you a clue.

For example, if grounding the wire in the test makes the gage go to "full" & that's what's happening to your gage when it doesn't work, then you could look for a worn spot on the insulation of that wire. I wish I could remember what the gage is supposed to do during that test!

Also, I never realized that the fuel sender lock ring-to-tank is part of the ground, but that makes sense. You just need to be SURE there's continuity between the fuel sender and the body..... add a ground wire if needed.

 

[James Pope]

Your just going to have to stay on top of it to get it figured out. My A100 did the same thing out of nowhere, fiddle farted around cleaning the fuel lines around the strap, the strap itself, etc. etc. and was working, then dead again for no reason. I did the thick wire with 2 hose clamps and removed the old strap trick and that worked for a while then died. Put in a new sender thinking it was going bad, nope, then my gauge didn't read right with the new sender. I lived with that while I did a good check out with the old sender, it's fine. Removed the new sender, cleaned the hole area for the ring, and everything else in the area again, got a new ground strap and put it all back together and crossed my fingers. All has been fine since. So make sure the round plate on the sender and it's mating surface are clean is the only thing I can think of. It's more of a nuisance then a problem to fix? The problem is you don't know where it's mucking up? Good Luck

I'll check the plate on the sender for sure next, it's just an enormous pain to figure this out. This is the last thing that doesn't work on the car, everything else works like a dream.

 

[James Pope]

Yep, you've either got a loose wire or the insulation has worn off the wire going to the fuel sending unit so it sometimes gets grounded or the fuel sender is on its last leg.

Now that I think of it, what does the gage do when it isn't working? Does it go to "empty" or "full". I think there's a fuel gage test where you just ground the one wire going to the sending unit & see what the gage does. I'm not sure, but that might give you a clue.

For example, if grounding the wire in the test makes the gage go to "full" & that's what's happening to your gage when it doesn't work, then you could look for a worn spot on the insulation of that wire. I wish I could remember what the gage is supposed to do during that test!

Also, I never realized that the fuel sender lock ring-to-tank is part of the ground, but that makes sense. You just need to be SURE there's continuity between the fuel sender and the body..... add a ground wire if needed.

The ground test for both the temperature sender unit and fuel sender unit pegs the gauge all the way "hot" or "full" if your gauges are working (prolonged grounding damages the IVR, though). And it didn't peg "full": it would read accurately, for example a few days prior I had filled up, then when it was working it read about 7/8 full. I drove it a bit and a few days later when it started working again I was on half a tank, which lined up with how much fuel I would be using. So I don't think the sender is wrong because when the gauge works it seems to be accurate. I will try making sure that it's not grounding anywhere it shouldn't, I've already checked the wires from the sender going through the trunk and through the cabin, only thing left is the connection in the instrument cluster which I'd rather not have to pull out.

 

[miller]

You just need to be SURE there's continuity between the fuel sender and the body..... add a ground wire if needed.

I can't tell you for sure, if those 'later' model cars have it, or not...but...
Yeah, sounds like a ground issue. One thing you might look at, under the car, the steel fuel line itself. Like on my 64, fuel line goes up to the body, just above the sending unit, and there is a steel clamp around the line, that fastens directly to the body. That' a positive ground, fuel line to body. Keep in mind, up front, the gauge also uses that common body ground, that's needed to make the gauge work. Of course, the ground strap you mentioned is also needed.

 

[James Pope]

I can't tell you for sure, if those 'later' model cars have it, or not...but...
Yeah, sounds like a ground issue. One thing you might look at, under the car, the steel fuel line itself. Like on my 64, fuel line goes up to the body, just above the sending unit, and there is a steel clamp around the line, that fastens directly to the body. That' a positive ground, fuel line to body. Keep in mind, up front, the gauge also uses that common body ground, that's needed to make the gauge work. Of course, the ground strap you mentioned is also needed.

I will check that ground as well. Hopefully that'll solve my issue. Most likely it's dirty, as were almost all the grounds on the undercarriage.

 

[miller]

Yup. Probably looking at a loose, or dirty ground connection. Could also be at the dash, too.

 

[James Pope]

Yup. Probably looking at a loose, or dirty ground connection. Could also be at the dash, too.

How would I look for an issue at the dash?

 

[miller]

How would I look for an issue at the dash?

Have to have an idea what your looking for...

Body/frame of the car is the main 'ground'. Okay, with that in mind, the dash itself, how it's bolted in, gets grounded. The instrument panel (or, part of it) also becomes grounded, and that ground connection is needed by many of the gauges. Gauges get ground, by how they are mounted, or a separate ground wire.
If you have, say one gauge not working, or acting up...'could' be the ground. Just figure which way it gets it's ground. You can pull the instrument panel loose, to get to the back side of the gauges...BUT...un-connect the battery FIRST!
Just use an ohm meter, to check for good ground connections. Needs to be done on bear metal, won't read through paint. Ground connections are usually made through bear bolts, and the threaded holes.

If there is a bad ground, could be rusty bolt threads, bolt just loose, and so on. If your still talking about your fuel gauge...pretty sure that gauge gets grounded through the circuit board, on the back side of the cluster. Circuit board gets it's ground connection through...panel/dash/body.

 

[tommytmopar]

You could substitute a jumper wire in your ground circuit. That way you can figure out if your ground at the tank is where you are losing ground.