Fuel sending unit grounding wire location

[em2b96p]

My fuel gauge is pegged past full. I've replaced the FSU with a new 24v unit as well as fuel gauge. It's still not fixed. I'm guessing the issue lies with a ground issue? I have looked in the TMs and can't find it. I saw the flow chart in the TM for how to diagnose this issue. All it said is to replace the wire. But doesn't show where this wire is. I really hope I don't have to drop the tank. Does anyone know where on the Humvee the wire grounds to?

 

[Mogman]

Welcome to the forum!
Have you put a meter on the sending unit wire #58 to see if it is grounded?
Also have you cleaned all the grounding points on the back of the engine and both sides of the firewall behind the inst. panel?

 

[em2b96p]

Welcome to the forum!
Have you put a meter on the sending unit wire #58 to see if it is grounded?
Also have you cleaned all the grounding points on the back of the engine and both sides of the firewall behind the inst. panel?

Thanks for the welcome!

I am good at replacing things but not so good at troubleshooting electrical issues. I do have a fluke multimeter but not sure exactly how to use it to see if wire #58 is grounded. Can you elaborate on that process please?

I have not cleaned the ground points. I did see the one on the back left of the engine and can try and clean that. However, I have not looked for the ground point in back of the instrument panel. Is it easy to find?

 

[Mogman]

There is a bolt going through the fire wall directly in front of where the inst. panel is mounted, you have to pull the panel to get to it, there are ground lugs on both sides of the firewall.
Put your meter in ohms (the sign of the omega) touch the probes together and note the readout, many times it will not be zero, then put one lead on the ground shunt Mounted on the inside towards the front of the battery box, then pierce the insulation on wire #58 at the sending unit and the reading should be close to what you read with the probes touching each other.
You can also pull wire #28 off of the sending unit and ground the end going to the gauge, open will be ether full or empty and shorted to ground will be the other, never can remember which as many types of vehicles are different, but you should see a difference between open and grounded.

You can also pull the wire #58 connection and ohm out the side going into the harness but I prefer to test all circuits in place, thus the piercing of the insulation

 

[em2b96p]

There is a bolt going through the fire wall directly in front of where the inst. panel is mounted, you have to pull the panel to get to it, there are ground lugs on both sides of the firewall.
Put your meter in ohms (the sign of the omega) touch the probes together and note the readout, many times it will not be zero, then put one lead on the ground shunt Mounted on the inside towards the front of the battery box, then pierce the insulation on wire #58 at the sending unit and the reading should be close to what you read with the probes touching each other.
You can also pull wire #28 off of the sending unit and ground the end going to the gauge, open will be ether full or empty and shorted to ground will be the other, never can remember which as many types of vehicles are different, but you should see a difference between open and grounded.

You can also pull the wire #58 connection and ohm out the side going into the harness but I prefer to test all circuits in place, thus the piercing of the insulation

I will try all of these suggestions. I will report back with results!

 

[em2b96p]

I will try all of these suggestions. I will report back with results!

I took apart the battery cables and cleaned all the grounds and terminals.

I also cleaned the ground on left side of the back of engine. I see the ground wire for fuel sending unit #58 and cleaned it too.

Then i moved onto the ground behind the gauges. I took that bolt out and cleaned it.


I grounded the wire from the fuel sending unit and the gauge pegged left below the empty line.

I havent tested the wires with the meter yet.


Problem still exists with th needle pegged past full.

 

[Mogman]

That means ether the wire is not getting to the sending unit, the sending unit is bad or the sending unit is not grounded, have you taken any resistance readings? you should be reading between just a few ohms to ground to around 90 ohms at the sending unit wire at the gauge #28 , if not it somewhere in what I mentioned above.
If you do read from a few ohms to less than 90 at the gauge then the gauge is defective or miss wired

 

[Mogman]

If you take the sending unit input to the gauge and ground it, it should read empty, if not you have a gauge problem.

 

[em2b96p]

I found the problem! The #58 wire that connects to the fuel sending unit was severed. I found it right above the heatshield of the muffler/resonator. I repaired the wire and now it works. Im not sure how it was damaged in the first place.