Fuel Gauge or Sending Unit Problem, Please Help...

Heres the problem. I just replaced both my fuel sending unit and fuel gauge and can't get it to work properly. I've already replaced the wiring and checked the grounding. Furthermore, I connected the sending unit to the gauge and jumped a ground wire as well. When the sending unit is set to full, the gauge shows full, however when I move the sending unit to empty, the gauge shows beyond full and pegs.

If I connect the guages sending unit terminal to ground, the gauge reads empty.

I ohmed out the sending unit and found that the unit reads 30 Ohms when full and 245 Ohms when empty.

The gauge responds to 30 Ohms Full and 0 Ohms empty.

What needs to be replaced, the guage or the sending unit? Both of these that are in the truck now are brand new and it appears that these are mis-matched.

The truck in question is a 1953 Reo M35 with a OA331 Gasser Motor.

The sending unit has the following numbers stamped on top of it:
4393286
19207S0CN12298209
57733

Thanks for the help.

Tyler

Here is part of your answer.

Think thats it. Must be a faulty sending unit. My sender is 30 - 245 Ohms. Thanks very much for the help! Will get another sending unit on order right away...

and the rest of the answer is that the sending unit is ORD 7526037, AC 1517364, RC 633H1 (REO), and SD 914449... Studebaker... have fun... RAM

Question: I have a 1968 Jeep M-35A2. My fuel guage is unresponsive - needle at empty.

Good wiring , guage and sending unit are "new" . Can "Cranetruck" or anyone provide a "most logical step method" objective: working fuel guage.

Little time - none to waste on ineficcient procedure.

Thank you.

fuel gauge problem

Masterchief,


Military fuel gauges are pretty simple things. They're a series circuit which means that the current from the battery goes thru the gauge to the sending unit and back to the battery in a single loop. The gauge deflects depending on how much current is flowing thru it. This is controlled by the sending unit, a simple variable resistor.


Positive voltage is applied to the gauge, usually thru the ignition switch. It goes thru the gauge over to the tank sending unit. If you connect the positive lead to the gauge and leave the other terminal open the gauge will read maximum. If you ground this lead the gauge will read minimum. If this doesn't happen the gauge is bad.


You can check to make sure you have good wiring between the gauge and sender by grounding the sending unit gauge at the gauge and checking the sending unit end with an ohmeter. When it's grounded your meter should read 0 ohms to ground. When it's not grounded it will read inifiity. If it reads 0 ohms the wire is good.


The last part of the system is the sending unit itself. they are a variable resistor who's value changes as the float goes up and down. With your ohmeter, read the value of the sender with the float up and then again with it down. It should be a smooth change in resistance. If the meter jumps up to infinity then the resistance windings are bad or the contact spring isn't making contact. I did have a unit in my 151 that actually had an open wire inside between the resistor and the external contact but that's fairly rare.


Read the resistance between the tank and the frame with your meter. It should be 0 ohms. A bad connection between the tank and the frame caused by rust will play havoc with your readings. Vehicles like the HMMWVs and Corvettes have supplemental ground wires because their bodies don't guarantee a good connection to ground.


Good luck


Kurt