340 fuel guage

Is there a way to check the sending unit and fuel gauge on a 340? I am having to remove the tank to fix a pin hole and I want to get the fuel gauge operational.

thanks
bass
53superC

A fuel gauge work by way of the sender changing resistance so you can apply voltage to the gauge and it should move from one side to the other when you do that. As for the sending unit you can move it while hooked to a VOM set in ohms and the reading should go up and down in resistance

The sending unit actually provides the ground for the guage -- if You ground the wire at the sending unit it should raise the guage to full -
- if it dont move the guage is bad -- considering it is being fed 12 volts to start with -good luck -- Roy

When I restored my Farmall 240 a few years ago I installed a grounding strip or buss bar from the aviation world behind the dash out of sight and view and grounded everything I could that needed a dedicated
ground to that strip. The strip in turn was grounded directly to the ground on the battery which eliminated most of all the items trying to be grounded through the chassis and it's many various components.
Rust, dust, dirt and corrosion are the main players in disrupting a good direct ground through the chassis on these old tractors. As I recall the fuel tank sending unit was originally grounded by it's
connection to the fuel tank while the dash gauge was grounded to the dash panel with a small pointed shape piece on the gauge unit which was held against the panel by slight spring tension. A good clean
unrestricted ground is absolutely necessary to have a functional fuel gauging system on your tractor. Your problem, if you are lucky, is just a grounding problem and after cleaning the tank unit and gauge
unit and doing a bench test it just might be functional by providing battery current and a ground system to your items. One word of "CAUTION", the gauge unit can only be hooked to 6/12 volt power on the
correct terminal on the back side or your dash gauge unit will be quickly toast. The other terminal on the back is to the tank sending unit which reads the resistance that measures the fuel tank level. Make
sure you label the current side of your gauge unit when removing from the tractor so as not to get them mixed up when replacing back on the tractor. You will also notice there are some insulators on the
mounting studs which contact the mounting bracket which must be retained and kept in place when installing back on the tractor. Good luck in working through your issue and if you find a new or replacement
fuel sending tank unit is needed post another thread as I found a source in my endeavors as it most likely won't be available from CaseIH if needed, Hal.

The sender in the tank provides a ?variable? ground.
Unhook the wire at the tank sender and turn on the power to the gauges. The gauge should register way full or way empty.
Then ground the wire you took offf the sender to the block or frame.. The gauge should swing the opposite way that it was?from way empty to way full, or vise versa.
If things work OK so far, the gauge, wire and power supply is fine. I would take a chance and assume the sender is good.
Or you can remove the sender from the tank and hook up the wire. Ground the sender mount back to the tractor. (Better yet, right to the appropriate battery post). Swing the float up and down. The gauge should respond. If it doesn?t, the problem is in the sender.
In my experience, it?s almost always the sender that goes bad. Sometimes th tank is not grounded well to the tractor frame (and appropriate battery post) so there is no path for the sender to complete the circuit.

You may also check the float .I have not removed the fuel sender on my 240 , but most sending units have a copper float or cork float . The copper can get pin holes that let the float fill with gas and sink giving an empty indication . Cork can deteriorate and fall apart and the float will sink . In the case of copper I have used an old carb float to attach to the arm .Sometimes you can find the correct float at the parts house .