Fuel sending unit

[Oldjarhead]

I'm new here and really need some help. I bought a 1985 M1009 CUCV for my daughter to drive. I have been fixing problems slowly and need some advice.


The fuel gauge is stuck at the 3 o'clock position and it appears that the fuel sending unit is bad. I found a three tube unit NOS for a great price but the unit on my truck is a four tube. Can anyone explain to me if I can use this one? If so how is it done?

The volt meter is also missing and I was thinking about putting in a temp gauge. Any ideas on that?

Thanks,
Joe

 

[tamecrow]

The fuel gauge is stuck at the 3 o'clock position

Did you check the sending unit for a good ground? Very common problem on these trucks.

 

[AceHigh]

Plus one on the grounding. Replacing the unit is not too much fun. The 3 tube is what you use, the military ordered the 4 tube so one could be utilized as a siphon drain, so if you can get by without that you are good to go.

 

[blackhueys]

Yep my ground wire broke off on mine it was a pain getting my hand in over the top of the tank to fix it the broken wire but been fixed ever since with no issues.

 

[combatmech]

Plus three on the ground wire.

 

[Mainsail]

The fuel gauge is stuck at the 3 o'clock position and it appears that the fuel sending unit is bad.

So the gauge is off-scale high?

Mine was stuck at ¼ full and only moved down from there. I did the troubleshooting procedure from the FM and the results said the indicator was bad. $60 for a new one and it's fixed. You start by disconnecting the ground wire which is bolted to the frame rail just above the left rear axle- can't miss it.

Find the voltmeter- you need that.

 

[Oldjarhead]

Appreciate the info. I checked the ground wire and it is solid. Traced the wires and everything looks good. Going to crack open the instrument panel tonight to replace the bulbs so I'll check those connections.
Thanks.

 

[Oldjarhead]

Appreciate the info. I checked the ground wire and it is solid. Traced the wires and everything looks good. Going to crack open the instrument panel tonight to replace the bulbs so I'll check those connections.
Thanks.

 

[Mainsail]

What happened when you disconnected the ground wire and put the key in Run?

 

[Oldjarhead]

Disconnected the ground and the needle didn't move.

 

[wayne pick]

I had the same problem a while back. I fiddled with a volt/ohm meter, got frustrated, electrical is not my strong point, so I replaced the sender, ran a new wire and installed a small 2-1/8 guage next to the bat/volt meter. Looks like it belongs there, and it's reliable.

 

[Skinny]

This is a very simple diag that I am going to try and remember. You pull the wire that feeds the guage. With the key on it should read max full or empty, can't remember which one. Then touch that wire to a very good ground. Again, key on...it should go to the opposite side of the guage. If it doesn't do a full swing when going unplugged then shorted to ground, the gauge is bad. If the gauge does a full swing, sending unit or sending unit ground is bad.

Not rocket science, this is a simple sure fire test.

 

[FridgeBrilliance]

Small update on this one. My gauge was stuck at WAY over full and would sloooowly move, and apparently (per previous owner) immediately hit half when it was empty, with no warning. I just went out with the headlamp and checked the ground. Totally solid. Unbolted it anyways and simple green douched everything, then sanded the frame rail, washers, bolt, and ground tab until shiny. Bolted it all back together and presto. Fuel gauge works fine. So don't trust the ground even if it is solid. If it is dirty and corroded, bust it up and clean it anyways.

 

[MarcusOReallyus]

checked the ground. Totally solid. Unbolted it anyways and simple green douched everything, then sanded the frame rail, washers, bolt, and ground tab until shiny. Bolted it all back together and presto. Fuel gauge works fine. So don't trust the ground even if it is solid. If it is dirty and corroded, bust it up and clean it anyways.

Bingo.




You cannot check an electrical connection by looking at it. Especially not a ground!


You must check with a voltmeter or take it apart and clean it. An outside visual inspection is about as trustworthy as a used car salesman's promise.


I was going to say a politician's promise, but I might get in trouble for that.

 

[wayne pick]

Hea Marcus, Youre the electrical guy, Im not. I have found that green corrosion inside some wires after stripping them. Does that have an effect on the wires ability to carry voltage or continuity? The fuel sender wire was visulally intact, but no continuity, so I got pi$$ed and replaced everything LOL.

 

[Oldjarhead]

I thoroughly cleaned the grounding wire connection and frame before trying the unhook test. The gauge is well seated into it's connectors.

 

[MarcusOReallyus]

Hea Marcus, Youre the electrical guy, Im not. I have found that green corrosion inside some wires after stripping them. Does that have an effect on the wires ability to carry voltage or continuity? The fuel sender wire was visulally intact, but no continuity, so I got pi$$ed and replaced everything LOL.

Yessir! It definitely does have an effect. How much of an effect depends on how much corrosion is there. It might be not noticeable, but it will only get worse with time.

If I see green stuff, I replace the wires. It's kind of like food - when it doubt, throw it out!

 

[Barrman]

Just so people looking at this in the future will have a reference. The -20 manual has a trouble shooting section on the fuel gauge and it spells out what the gauge should do when you have the lead to the sender unhooked and grounded.

The gauge that only goes to 1/2 when the tank is full is normally a bad sender. But, always check your grounds and all connections before going to the trouble of dropping the tank.