Can't get fuel sending unit to work.

[ton10291]

I've purchased 2 new fuel sending units and can't get either to work. I measured the resistance out of the tank at the sending unit and at the gauge and found both to work but installed in the tank neither works. It seems like the floats aren't buoyant enough to raise the levers but checked in a tub of water they work fine. I'm installing with the connector pointing toward the rear of the truck which positions the lever and float toward the passenger's side of the truck.

What am I doing wrong?

 

[98taco3]

If you have a good gauge and a good connection between the gauge and the sending unit it may be a ground issue. Have you run a ground wire from the sending unit to to a good clean ground on the frame? Give it a try and see what happens. You can test the gauge by grounding out the connector to the sending unit on a bare piece of metal on the frame somewhere. The gauge should move when it is grounded out. Hope this helps!

 

[ton10291]

Thanks. I'll check the ground again but there is a ground from one of the sending unit mounting screws to the frame and the gauge operates fine when I test the sending unit out of the tank - I move the lever up and the gauge reads full then I move the lever down and the gauge reads empty.

It really seems like the lever is binding or the float is sunk when the sending unit is in the tank but that is really odd as I've tried 2 new sending units and see the same behavior. Also, the unit operated fine in a tub of water.

 

[David_4x4]

I dont know where or who you're getting you sending units from.

But a lot are cheap reproductions from somewhere overseas that just wont work period. A lot of places are offering these as original NOS or what not.

 

[longshot2171]

Is your new sender compatible with your current gauge?
When I got my truck it had the old style guage (metal conn) and a new fuel sender( rubber conn). At full float, it only read 1/2 full. I picked up a newer style used surplus guage and it is now almost spot on.& has all the bounce and slosh action that you would expect.

 

[ton10291]

The senders came from AB Linn and A1 Army Supply and they are identical. I thought that maybe the float on first unit was defective so I bought the second but am having the same problem.

The gauge is the metal connector style so it reads half when the lever is all the way up. I hope to replace it with the rubber connector gauge one day but I still can't figure out why the the gauge will work when I manually move the sender lever up and down out of the tank but when in a full tank the float doesn't seem to lift the lever enough to give anything but a near empty reading on the gauge.

 

[longshot2171]

Did you try running a 2nd ground line from the unit to the tank/frame?. When you say it's not working, does that mean that the guage is dead at empty. Does the needle move at all?
When you compare the new units to your original, are the float arms bent at the same angles and point in the same direction?

 

[ton10291]

Did you try running a 2nd ground line from the unit to the tank/frame?. When you say it's not working, does that mean that the guage is dead at empty. Does the needle move at all?
When you compare the new units to your original, are the float arms bent at the same angles and point in the same direction?

I gave a 2nd ground a try but no help. The gauge jumps to just above empty when the ignition is switched on and the tank is full.

It really seems to me like a mechanical problem with the sender. It's as if the float were just a little too heavy or the lever is binding when immersed in fuel.

 

[Bill W]

Usually with the holes on the sender it will only mount on the tank one way but make sure with the positon you have it installed ( connector pointing towards rear ) the the float swing arm is not hitting against one of the tank baffles and causing it not to move...just a thought

 

[longshot2171]

If you want to test to see if it is the float, pop it out and put a champagne cork in its place. make sure that the float arm is bent to the same angle and direction as the original. If not then that will effect the reading.

 

[orren]

On my truck, M36A3C, the rubber connector faces to the center of truck; might be worth a try?

Also, please let me know a good place to get a fuel sending unit replacement.

Good luck.

If you want to test to see if it is the float, pop it out and put a champagne cork in its place. make sure that the float arm is bent to the same angle and direction as the original. If not then that will effect the reading.

 

[popz76]

This is my problem as well...the previous owner had changed out the original sender and replaced it with I don' know what and ran a direct line to the gauge...read full all the time. I got a sender from Ablinn and installed it this morning using the already mentioned wire to the gauge. The sender works in and out of the tank perfectly but the second I put a screw in to fasten it down, it goes to empty. I did ground the sender as well and used a cork gasket. What next please !!!

 

[majorhitt]

First is your M 12v or 24v? Second , check ground between the fuel tank and the frame with an ohm meter, a zero reading should be obtained. The correct fuel sending unit for a M37 should read between 0 and 40 ohms. If it's higher replace it. The ohm meter should indicate a higher reading as the tank is filled and a lower reading as fuel is removed. Another thing is very good contact is important in electrical. Don't expect that the screw going through a hole is a good contact.

 

[majorhitt]

popz76 Not knowing all the if ands or butts with your case, lets say the power comes from a circuit breaker then to your gauge then to the sending unit. The gauge should be grounded and the sending unit should be grounded. The vehicle frame is the neutral wire. This makes a complete circuit, Power supply, indicator and, device. Now you said that as soon as you fasten the sending unit it drops off. This sounds like a short circuit. Look at the wires at the gauge, anything unusual? Is it that they are on the wrong terminals? You said it works in and out of the tank. How does it work out of the tank with no connection for grounding? Once more, A power wire goes to the gauge, then another wire goes to the sending unit from the gauge , no other wires needed. Make sure the wire that was run as a direct line is good not shorted to the frame. Hope this helps

 

[jimmcld]

If it quits working when you put a screw into the tank, there must be a short in the sending unit. The terminal going to the guage should not be in direct contact with a ground. It should be going through the resistance of the sending unit. Check the resistance between the terminal and the body of the sending unit with the unit removed from the tank. It should vary with the movement of the float. If that's ok, you may have one of the terminals on the back of the guage shorted to ground.

 

[popz76]

Thanks for the advice guys, I'll check it in the morning and see what happens !

 

[popz76]

Ran new wire, grounded good to the frame and I'm good to go again...thanks again all and Merry Christmas !!!

 

[timmmaaa06]

I have a question my fuel sender and guage works but is off by 15 gallons is there a way to calibrate the guage or something also the oil pressure and engine tempature seem low to if there is a way to check them. they do work but i dont know if reliabily. thank you

 

[timmmaaa06]

I have a 53 dodge m37

 

[WarrenD]

Is your truck 24V? As an aside, these gauges are not going to work like the modern ones. Mine bounce all over the place when I'm running and my oil pressure gauge and sender don't match (Have a 0-120 psi gauge and 0-60 psi sender which means my oil pressure reads 90 psi but it's really 45 psi)
You may want to check and see if your gauges are correct for the truck regarding type, voltage and range. A mechanical oil pressure gauge will verify that the oil pressure gauge is working correctly. You might have low oil pressure in the engine or it might be that you have a 0-120 sender and a 0-60 gauge (which would result in the gauge showing 1/2 of what it really is).
Senders can drift as windings short out, so I wouldn't be surprized if the various senders are on their way out.