fuel gauge not working properly

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

Post by Depthcharge » Fri Jun 13, 2014 3:43 pm

I just installed a new fuel gauge (24 volt) and new fuel sending unit in my M151A1 jeep. When I place power (main switch) to system the needle pegs all the way over beyond full. I have a little over 1/2 tank level of fuel. Has anyone ran into this problem before? It seems with new gauge and sending unit fuel gauge should work. Any suggestions would be appreciated. Thank you.

Steve Sr.
Springfield, Oregon


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D Pizzoferrato
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Re: fuel gauge not working properly

Post by D Pizzoferrato » Sat Jun 14, 2014 3:54 am

Steve,

Are you sure the gauge is wired correctly. The Packard connectors on the harness and gauge are molded to indicate where they mate. There is a smooth bodied connector and there is a connector with a series of bumps molded around the perimeter. Match smooth to smooth and bumps to bumps.

If the wiring is correct, you need to be aware that the M151s and A1s had notoriously poor grounding of the instrument panel. At some point, the A2s came with a grounding lead on the panel. Check panel grounding as well as fuel tank grounding.
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Re: fuel gauge not working properly

Post by Depthcharge » Sat Jun 14, 2014 6:12 am

Thanks for the reply David. Are you saying that the two wires on the back of fuel gauge might be switched? When I turn on main power switch and the fuel gauge needle pegs beyond full I took it that I had proper ground on the gauge housing and panel for gauge to work. All my other gauges work fine.

The fuel gauge needle pegged the same way with old gauge and gas sending unit. I thought the symptom of gauge pegging beyond full would be a key to the problem and that a member had run into this situation before. I am a disabled vet and it is difficult at times for me to accomplish even simple tasks. I will check for the bumps on the wires and if you have any other ideas why gauge is pegging over full, please let me know. I really appreciate your assistance.

Steve Sr.

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Re: fuel gauge not working properly

Post by svramselaar » Mon Jun 16, 2014 1:48 am

hi

the meter is working correct
if the wire at the tank gets ground (or a short to ground )the meter go at empty
if the wire at the tank is open (not connected or broken wire ) the meter go to full tank

george
1976 ? M 151 A2 AMG MUTT lost in acsedent
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Re: fuel gauge not working properly

Post by Kurt Lesser » Sat Jun 21, 2014 6:10 am

The ribbed connector on the gauge is the +24v feed to the meter. Try running a wire directly from the smooth connector to the sending unit and see what happens, you could have issues in the harness. Something else to try is use a multimeter on the resistance scale and make sure the sending unit shows some resistance value. Just because it was NOS doesn't guarantee it works. You can also check for continuity in the harness. Remember all of this stuff was made by the lowest bidder!
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Re: fuel gauge not working properly

Post by Depthcharge » Mon Jun 23, 2014 9:55 am

George hit the nail on the head. Thank you George. I checked that fuel gauge and panel plate were grounded as well as the gas tank sending unit. Then I placed my meter on continuity and checked wire from sending unit to the gauge. Sure enough, when I jiggled the wire the continuity would change, I have a break in the wire about 4" from sending unit. I spliced in a new wire and mail plug and the fuel gauge works fine. What George stated about fuel gauge pegging on full worked like a charm. This will go into my M151 Bible of important notes. Thanks everyone for you help.

Steve Sr.

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Re: fuel gauge not working properly

Post by Eddie Holland » Fri Apr 03, 2020 7:59 pm

So what is the problem when the gauge always shows empty?
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Re: fuel gauge not working properly

Post by markrdje » Fri Apr 03, 2020 11:09 pm

No gas
change user name to mark

Rickf
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Re: fuel gauge not working properly

Post by Rickf » Sat Apr 04, 2020 4:37 am

:lol: :lol: :lol: :lol: :lol: Classic!

Bad gauge or no connection would be my guess.
1964 M151A1
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Re: fuel gauge not working properly

Post by mrvtwin95 » Mon May 25, 2020 3:52 pm

Team,

It's not over! I have a fuel gauge issue too and need guidance. I have a new sending unit and a gauge that has been untested by me.
Tank is full of fuel. 8) Gauge reads empty.

1. Tested voltage at sending unit: 24.65 volts
2. Made sure connectors at gauge are properly connected (smooth to smooth etc.)
3. Checked resistance of sending unit: 2817 ohms
4. Pulled connector at sending unit...no change on gauge (reads empty)
5. Made sure panel was grounded.
6. Put another known good fuel gauge...nothing. Reads empty.

So, is the resistance too high on sending unit? When I turn the ignition on I notice a little tick or bump on the gauge (the needle).

Any new ideas? Thanks in advance!

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Re: fuel gauge not working properly

Post by Rickf » Mon May 25, 2020 5:41 pm

The tank sender should be 30-90 ohms if I remember correctly. 2817 makes no sense at all. If that is the true reading between the post and the ground terminal then the sending unit is bad. Also make sure the tank is grounded to the body, a quick way to test this is to run a jumper cable from the sending unit body to the ground terminal of the battery and see if hat changes anything. The tank gets its ground at the clamp where the tank is held down. Also make sure the wires are on the gauge correctly. I am thinking that open circuit (as in unplugged at the sending unit) should result in full reading on these.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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Re: fuel gauge not working properly

Post by mrvtwin95 » Tue May 26, 2020 4:12 am

Hmm so I tested the resistance of the sending unit by putting the Fluke between the sending unit post (with power off) and one of the bolts that is holding the tank down. I used this same bolt to measure voltage at the unit as well and got the 24.65 volts.

I also ran a wire from the gauge (smooth connector) to the sending unit but want to make sure..do I go to the post with it? or ground? I have double check correct gauge connections...good.

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Re: fuel gauge not working properly

Post by Rickf » Tue May 26, 2020 4:52 am

I would measure the resistance between the post where the power wire comes in, with the wire disconnected, to the body of the sending unit unless there is a ground wire tab on there. I have seen them with and without. Measuring voltage and measuring resistance is two totally different things so the bolt may have shown voltage but it was not showing any resistance that may have been there. You want to know if the gauge unit is good or bad before you start chasing wiring. The aftermarket sending units have a terrible reputation for being bad right out of the box. China's best!
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone

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Re: fuel gauge not working properly

Post by mrvtwin95 » Tue May 26, 2020 5:22 am

Rick,

After your comment on the sending unit resistance...I checked it again. It's reading 28 and change :D . My eyes didn't see the decimal point. But even then with the sending unit unplugged my gauge doesn't move at all and just sits at empty. Do you have any ideas on testing the gauge itself? Thanks for your help!

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Re: fuel gauge not working properly

Post by Rickf » Tue May 26, 2020 12:43 pm

Well, that reading makes more sense and it indicates a full tank. You are SURE you have the positive wire going into the positive side of the gauge and the negative wire from the gauge going to the tank? The gauge should be marked somewhere positive and negative.
1964 M151A1
1984 M1008
1967 M416
04/1952 M100
12/1952 M100- Departed
AN/TSQ-114A Trailblazer- Gone


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