fuel gauge not working properly

1959 - 1978, M151, M151A1, M151A2, Technical questions and discussions, regarding anything related to the M151.
mrvtwin95
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Re: fuel gauge not working properly

Post by mrvtwin95 » Tue May 26, 2020 7:40 pm

Rick,

Yeah basically I matched the connectors to the gauge. Specifically the "grooved" plug to the "grooved" connector and the smooth plug to the smooth connector. I went ahead and bought another sending unit. I mean I get 24 volts at the unit but no "feedback". So we'll see. Thanks again for your help.


Rickf
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Re: fuel gauge not working properly

Post by Rickf » Wed May 27, 2020 4:47 am

Well, the reading on your sender is right on the money, disconnecting the wire has no effect, those two things would lead me to believe that the problem is not the sending unit. I realize you hooked up the wires according to the rubber connectors but if this is an offshore gauge that means nothing. I have seen them set up backwards before. And as George said, an open connection will cause the gauge to read full. so I am wondering if yours is even getting power.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

svramselaar
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Re: fuel gauge not working properly

Post by svramselaar » Thu May 28, 2020 12:50 am

hi

if you reed between the lines
you must take the wire from the tank element
if it stands empty take the wire from the meter (no 28 )
if it is then at full you have a short at the wire from the meter to the tank
to test you can also take wire 28 from the meter and take a new wire from the meter to the tank element
if this works you have shore a short at wire no 28

george
1976 ? M 151 A2 AMG MUTT lost in acsedent
1978 M 416 A1 ( parkhurst ) trailer
1970 m151 A2 FORD BUDD tub
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mrvtwin95
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Re: fuel gauge not working properly

Post by mrvtwin95 » Sat May 30, 2020 4:12 am

Rick,

So my new sending unit arrived and I installed. No change. The gauge reads empty. Somewhere on this forum a member mentioned to take the connectors off of the Oil Pressure gauge and connect the fuel gauge connectors. There should be a result and this will tell you if the connectors are good or not as it "powers" up the oil gauge. I did this and got nothing. Question: wire number 27 to the fuel gauge, where does it lead to from the gauge? I was thinking of checking continuity. This whole thing is crazy. BTW, i know grounding is crucial so I put and alligator clip on some metal flange on the back of the instrument panel to a bare bolt connected to the body of the jeep. Again , I am getting 24 volts to the sending unit.

Rickf
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Re: fuel gauge not working properly

Post by Rickf » Sat May 30, 2020 4:50 am

If you are thinking #27 goes to the gauge then you have your problem. #27 is a power wire that feeds the system and #28 goes to the gauge. It leaves the gauge, goes out under the dash to the connectors to the rear harness, the #28 wire in the rear harness goes to the sending unit. But you are on the right track now, checking continuity on the wire from the gauge to the sending unit is definitely high on the list. From what George is saying you may have a ground in that wire. I am still not convinced the gauge is wired right though. I don't have a spare fuel gauge here to look at and see if it is marked + and - but I seem to remember seeing that on one that turned out to have the runbbers on wrong. I may have a spare for my M37, I will see if I can find it today and get the proper orientation from it.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

Rickf
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Re: fuel gauge not working properly

Post by Rickf » Sat May 30, 2020 5:37 am

Here is something to try. Take a jumper wire and attach it to the sending unit terminal of the gauge, turn the switch on and ground the other end of that jumper. I am thinking the gauge will go to full. I looked back at the M37 troubleshooting and that is the diagnosis for the M37 and that is what has always been done for years on most cars. I don't want to say George is wrong but I want to make sure the manual is also not wrong. The gauges for all M series are the same. IF the gauge goes to full then you have a broken wire going to the sending unit.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

markrdje
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Re: fuel gauge not working properly

Post by markrdje » Sat May 30, 2020 2:38 pm

Ya I did the same as rickf said, only that I took the wire off the gas tank sending unit, grounded that wire with the mutt running watching the fuel gauge, it went to the full reading.So the gauge is working. Leaving the key on could lead to other problems if my
memory is working right.I've had alot of times with the gauges not working cuz of poor grounding.
In one of my cars I'd hit the dash to get the radio working(the speaker had a loose ground, LOL)I am just giving my 2 cents worth.
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mrvtwin95
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Re: fuel gauge not working properly

Post by mrvtwin95 » Wed Jul 01, 2020 5:32 am

Team,

Just for closure, I put a new gauge in and now it works... Thanks!

Hanselandgretel
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Re: fuel gauge not working properly

Post by Hanselandgretel » Thu Oct 15, 2020 5:26 pm

There are good troubleshooting guides in the manuals. Follow them and it should tell you which part to change or look at.

I always hook up fuel gauges and senders on the bench with clip leads before I install them. It is a lot easier to solve problems before these parts are installed in the vehicle.

markrdje
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Re: fuel gauge not working properly

Post by markrdje » Thu Oct 15, 2020 5:30 pm

That's a good practice cuz new stuff doesn't always work.
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Gary Turman
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Re: fuel gauge not working properly

Post by Gary Turman » Tue Oct 20, 2020 5:58 am

I installed a new sending unit and it was working fine at first then quit working. Turned out the float wasn't sealed good and it was full of gas. I had kept my old unit and used the float off it. All was good again. The bad float was new so that might be something to check if it just stays on empty.
1941 Dodge WC-7 Command Car
1942 Ford GPW
1968 M151-A1
1967 M416
1945 Gemco 1/4 ton trailer
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Tech3140
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Re: fuel gauge not working properly

Post by Tech3140 » Sun Mar 27, 2022 8:21 am

I also have a fuel gauge problem as well.
I replaced the fuel tank because the seam between the filler cap and tank separated Big Time.
Found the cause of that, almost ruined that tank as well.

Also installed a new fuel guage. Now this happens.
With 15 gal of fuel in the tank, it reads 1/2 full.

Everything is correct. The wire is correct, connectors are correct resistance and voltage are correct.

I’m thinking that the sender is eather bad or needs to be adjusted.

Rickf
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Re: fuel gauge not working properly

Post by Rickf » Sun Mar 27, 2022 11:27 am

With the sender out of the tank and you raise it all the way up does the gauge go to full? You will need a ground wire hooked up to the unit while doing this. If it does then you will need to bend the float arm down so that it raises the base end of the arm higher as it comes up. You can bend the arm a little down from the electrics so you do not damage them. If you still have the old unit compare them to see if the arms and floats are in the same positions.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

hambone
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Re: fuel gauge not working properly

Post by hambone » Sun Mar 27, 2022 1:11 pm

Do as Rick said but they are not known for their accuracy, more like an estimate. :lol:

markrdje
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Re: fuel gauge not working properly

Post by markrdje » Sun Mar 27, 2022 1:22 pm

I always carried a lath stick with me to be sure
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