Fuel Gauge Fun

[erikhillard]

not sure why the photos preview flipped, but if you click on them they display correctly

Heya.. for a long time I've had the usual 3/4 fuel gauge activity when full. Changed the tank sending unit more than once over the years and no change. Changed out some wiring the last time to make sure grounds were solid. Swapped in a dash voltage regulator and removed the wound wire radio thing.

When I pull the black ground wire off the sending unit and touch it to the red center wire/post on the sending unit the fuel gauge pegs to Full. So to me that tells me the wiring from the tank to the gauge is all good and the gauge should be fine too.

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The fuel tank is definitely not a 1968. Has vents that I had to seal up a long time ago. Clearly from a later model. Now I'm starting to think that the sending unit is just the wrong one for the tank?

The tank with venting tubes that had to be connected up so it wasn't venting into the cab. I'm using a vented gas cap.

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Why? Well today the gauge was reading 1/4 tank. I put in the new voltage regulator cause I was in there replacing wiper gaskets. Went to the gas station and filled the tank until I could see gas. 14.8 gallons! Gauge now reads 3/4. WTF, how can it be 14.5 gallons between 1/4 and 3/14? Its a ~19 gallon tank from what I recall?

After topping off the tank

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[cep62]

Have you ever taken the unit out and worked by hand ?

If it works that way , you can bend the float arm to raise the level.

[erikhillard]

I feel like I did at some point when swapping the sending unit. Guess I could pull it out and try that. But my thought was if the tank is so full that I can see gas in the filler neck, how can the float not be maxed out? Thats why I was starting to think I have the wrong sending unit in the newer tank?

[cep62]

how can the float not be maxed out?

The float can be maxed out , but it might not be pushing the sending unit all the way.
If you bend the float down , when it comes up the sender is going farther towards full.

so if it works out of the tank , that might be the solution.

[erikhillard]

Thanks for the clarification. I'll give that a shot today.

[erikhillard]

Nope, with sending unit float maxed height the gauge stops at 3/4. There were some poorly sauntered connections on the sending unit and I made them secure but no difference.

Again, if the black ground touches the center red of the sending unit, the gauge goes to full. Does that mean the sending unit is bad?

I wonder if sending units are available at local auto parts stores. I believe the previous two I've ordered over the past ~10 years were likely from LMC or Dennis Carpenter.

[erikhillard]

With my voltmeter..

get 5V when power unhooked from sender unit and clipped to power wire and ground wire.

get 2.5V when power hooked to sender and clipped to sender post and ground wire.

[basketcase0302]

"cep62"

how can the float not be maxed out?

The float can be maxed out , but it might not be pushing the sending unit all the way.
If you bend the float down , when it comes up the sender is going farther towards full.

so if it works out of the tank , that might be the solution.

I would have bet money on the float arm needing tweaking also.

Try getting an ohm reading from the sending unit and see it it compares to the specs here:
http://www.fordification.com/tech/fuel- ... -units.htm

I'd also be very surprised to see ANY new replacement sending unit from DC to be defective, (maybe LMC-but not DC).

[erikhillard]

"cep62"

how can the float not be maxed out?

The float can be maxed out , but it might not be pushing the sending unit all the way.
If you bend the float down , when it comes up the sender is going farther towards full.

so if it works out of the tank , that might be the solution.

I would have bet money on the float arm needing tweaking also.

Try getting an ohm reading from the sending unit and see it it compares to the specs here:
http://www.fordification.com/tech/fuel- ... -units.htm

I'd also be very surprised to see ANY new replacement sending unit from DC to be defective, (maybe LMC-but not DC).

With the sending unit OUT of tank and arm all the way up, gauge only goes to 3/4 full. Bending it is not going to help at all here. When I bypass the sending unit tho, gauge goes to Full.

I was looking at the Fordification group on Facebook and found someone with a similar issue. He got another sending unit that looks much more like the original ones and it works fine. The newer looking one on the right (which looks like what I got from DC) gives him a 3/4 rating while the old one works great. I'm ordering up another one from NPD and will see what arrives.

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[basketcase0302]

Erik,
Understand about the arm, (I was just agreeing that is a common found issue like CEP62 stated above).

Hard to believe that DC would be selling us Chink crap, (just went through TWO china aftermarket fuel relays before finally getting a Motorcraft which solved the issue). NPD rocks, I built almost my entire last truck using them.

[390FE1972]

Let us know if this works out for you, I am going thru the same thing! I have replaced the fuel sending unit with a new one and having the same issue. It will be good to know what works for you.

Regards

[erikhillard]

Let us know if this works out for you, I am going thru the same thing! I have replaced the fuel sending unit with a new one and having the same issue. It will be good to know what works for you.

Regards

Where did you get your new one?

My NPD order is supposed to arrive today and I'll get right on the swap as long as its not raining. The NPD site didn't have a photo of the unit, so I've got my fingers crossed its the older looking repro style and not the newer design I got from both LMC and DC over the years.

[erikhillard]

IT WORKED! The sending unit from NPD goes to full. First time in 15 years I had a working gauge. And basically it was because the two sending units I bought over the years were just not the right one I guess?

Highly recommend getting the repro one from NPD if your gauge says 3/4 and your testing shows the gauge goes to full when you touch the ground to sending unit center post.

Sending unit in the foreground with gasket is the new repro one I got from NPD
The farther one was from DC I believe in ~2018

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[erikhillard]

Here's the direct link to the NPD part that worked for me

https://www.npdlink.com/product/sending ... ?year=1968

[The Bandit]

Glad to see that worked out for you! I on the other hand had the opposite problem. When I ordered my tank from lmc I forgot to order the sending unit as well so being that npd and DC are local to me and I was right by npd I stopped in and got one from them. I was never able to get it working properly and the one time I did get to read close to full I ran out of gas while still showing just over a 1\4 tank left in it. The one I got from DC worked out for me and I never had a problem again with it.

Good luck with you truck!