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Discussion Starter #1
Hello everyone! Long time lurker but first time poster here.

I have a problem with my fuel gauge working so I searched every forum I knew to search including YouTube and Google; I think I may be able to stump some of you gurus here...

The problem: my fuel gauge is not reading the fuel level; it only shows empty.

What I’ve tried:
1. Remove the sending unit and check resistance. Ohms read around 10 at empty and 70 at full (give or take) and the internal contact is making good contact with the resistance wire. I have confirmed this.

2. Ground the wire going to the gauge. This is the one from the sending unit in the trunk and I’ve held it to a ground; then the Gauge pegs at “Full” so I know the gauge works

3. Checked the float. The brass float floats strongly in water so I know it hasn’t sunk.

4. Confirmed clear sock. The sock on the pickup tube is very clean; I replaced this unit 4 years ago with a 3/8” size from NPD and it worked great until around 3 weeks ago. I know the sock may be unrelated but why not check it at this point.

My suspicions:
A) the float arm isn’t allowing the float to rise for some reason... haven’t confirmed yet

B) the sending unit itself isn’t making a good ground with the tank/chassis.

Any ideas? I have less than 5 gallons in the tank so I can drain it again if need be.

Thanks!
Jordan
 

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It should read 73 ohms Empty and 10 ohms Full.

Is your tank grounded?

Have you tried hooking it up outside the tank with a ground wire to see if the gauge moves when you manually move the arm?
 

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Discussion Starter #3
Thanks for the quick reply. “No” to both of those. I’ll drain the tank and test the resistance of the unit as well as ground the tank itself and post back with the results.
Thanks
JT
 

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Discussion Starter #4
Ok, sending unit is out of the tank and in the trunk; gauge wired to sending unit post and unit body is grounded. The Float arm is pinned at max and the gauge reads at just under full. Good idea to check that...

So I’m guessing either the unit isn’t grounded to the tank completely or the tank isn’t grounded to the chassis completely?
 

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That would be my guess. A lot of times new tanks have too much sealer along the mounting lip and the screws aren't enough to make a good ground.
 

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Discussion Starter #6
Ok Well this is actually the original tank. I removed and cleaned it when I put the new sending unit in 4 years ago to get the rust out but I just removed a bolt and it had no bare metal showing at all. I’m making a ground strap that I’ll install with a self tapping screw through the tank lip and connect to the chassis to see if that corrects the problem. I’ll need to pick up a new connector in the morning but I’ll keep you posted.
 

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Discussion Starter #7
Ok I put the sending unit back in the tank after confirming that it works outside of the tank and put 4 gallons of fuel in. It still wouldn’t move the needle so I added a ground strap through the tank mounting lip with a self tapping screw into a new hole. I then connected that strap to a chassis ground that I know is good. Still no needle movement. I added a new screw in place of one of the original tank installation screws after cleaning the surfaces and the hole.

I’m still stumped. Could the sending unit not be making good contact with the tank?
 

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Discussion Starter #10
Ok. A few things happened since the last post. I went to the garage and my gasket must not have set well so it was slowly leaking. I drained and removed the tank and then wire wheeled the tank lip, the trunk lip where the two meet, and the mounting hole for the sending unit including the locking ring tabs down to bare metal. I also wire wheeled the mounting screws. Then, I clipped the sending unit to the arm up “full” position under the car, hooked the gauge wire up, and then using another wire grounded the unit to the freshly wire wheeled tank at the opening.
The gauge pegged at “full”. Great!!

This means that if the arm is articulating in the tank and the sending unit is grounded to the tank, I’m operational again. So I put about 6 gallons in, turned the key to “on” and now nothing; just reading empty.

Thinking that the unit must not be grounded to the tank with the rubber ring gasket, I bridged the unit to a chassis ground that my battery is connected to. Still reading empty.

Any more ideas??
 

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I would guess that either the arm isn't moving up when you're putting fuel in the tank, or for some reason, the sender isn't sending a signal to the gauge with just 5 or 6 gallons in the tank. Have you tried filling up the tank all the way to see if that registers?
 

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Discussion Starter #12
I have not. I can try that though.

Do you know if any clever tricks to know if the arm is moving? The only think I thought of was to stick a steel coat hanger or other wire type object down in the tank and see if I could manually move the the float arm and see if the gauge moves...
 

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... then wire wheeled the tank lip, the trunk lip where the two meet,
There should be a sealant between the tank lip and the body. This is necessary to keep noxious fumes out of the car. 3M strip caulk is what's been recommended here many times. I guess the tank is supposed to be grounded through the mounting screws and not direct metal-to-metal contact between the tank and the body.
 

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I have not. I can try that though.

Do you know if any clever tricks to know if the arm is moving? The only think I thought of was to stick a steel coat hanger or other wire type object down in the tank and see if I could manually move the the float arm and see if the gauge moves...
You could do that and have someone up front checking the gauge to see if it moves. You won't know if it's accurate doing it that way, but at least you'll know that if the arm moves, the gauge registers.
 

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Discussion Starter #15
Ok so I think my car is hitting puberty; strange things are happening at inappropriate times...

I digress. I bought an extendable mirror and used it and my light to look into the tank and confirmed the float sank. Which sucks.
Now after fixing a minor distributor problem I got the car fired back up and the gauge reads just below 1/4 tank which is about right, so I go put 4 ish gallons in and....... no change; until I fire it up later at it reads just under half until i get back home and it reads just over 1/4 again.
Does this sound consistent with a sunk float to you guys?
 

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You can buy a brass float if u want to keep the original sender. Or just buy a unit. I’d buy the best one you can. NPD has several listed. Some are more linear than others.
 

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I just stumbled on your thread. You can easily test if the float is moving when adding fuel by connecting an Ohmmeter between the post on the sender & a known good ground. In post #2 TheRktmn says at empty the resistance should be 73 Ohms. So by adding fuel & reading the Ohmmeter the resistance should decrease gradually. If so this will confirm movement of the float.
 

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Discussion Starter #19
Yeah I’m draining the fuel now and planning on either replacing the float or finding the leak and soldering it up.

As far as the resistance goes, i did bench check it and the resistance was almost dead on spec so I’m confident it’s not any of the connections.

this is actually an NPD unit I bought maybe 7 years ago because I needed the 3/8 fuel pick up. I may end up ordering another float from them.

I really appreciate everyone chiming in on this! I’ll keep you all posted.
 

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See what GT_SCODE said: The float may be full of gas on not floating. It sounds like the sender itself is good. With as much trouble as everyone has with the aftermarket senders I would keep the one you have and just change the float. The new ones usually don't work with the stock gauges.
 
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