fuel tank sending unit 52 Ford

[whb52ford]

I'm using the sending unit that came with the car. Car still 6v

Up north my gas gauge worked fine. In Florida I had issues with the heat expanding the gas and puking gas all over. Pulled the tank several times, had it cleaned, and painted it. (Vented gas cap fixed it) Now fuel gauge works only some of the time, Tried another gauge back at the gas tank and same readings. Pulled the tank and run a ground wire from sending unit to frame. Got into car, turned key on, and it went to half full (about right) and slowly goes down to a little under 1/4. Waited a couple hours and started the car. Back up to 1/2 and slowly back down to 1/4.

I'm guessing the sending unit is working since it's sending the correct signal to the gas gauge. The new ground wire made no difference, but at least now I know I do have a good ground. What is causing the gauge to drop to the 1/4? If it was the float, it would not reset itself.

Stumped

[Drbrown]

Apparently your sender is adequately grounded thru its mounting on the tank and the float and your dash gauge is functioning ok.

Since the sender sometimes sends pulses to the gauge, and sometimes does nothing, I suspect that once the ignition is turned on, the tiny wire winding in the sender unit is perhaps warming-up and either its resistance is changing or the winding warms to a point when no pulse is sent out. If you can remove the cap on the sender unit, try gently spraying some electronic cleaner on the mechanisum. I have tested my sender by removing it from tank, running a ground wire to it, and while holding it level, raising and lowering the float arm to see what the gauge reads. Its possible the wire winding inside the sender is broken at some point and pulses are only "sent-out" depending on how the float arm sits.

Otherwise, a gauge-fixer person could properly test the sender.

If at all possible, I do not recommend replacing the stock sending unit with a new/aftermarket unit. Sometimes they work; sometimes not.

Another option (a poor connection or flaw in the wire from the sender to your gauge, and its resistance may change when electricity is flowing thru it) BUT since a different gauge shows same problem when connected to sender, I think the problem is in the sender.

[19Fordy]

HOW TO ADJUST FUEL TANK SENDING UNIT FORDBARN 3/7/2019

Whb52ford: When that same thing happened to my King-Sealy 6V Ford fuel tank sending unit I did this:
1. Remove sending unit and see if float contains any gas. The brass can develop hairline cracks which allows gas to seep in and give a false reading. This is very common. Either repair the float with electrical solder (has low melting point) or install a new aftermarket brass float. Also carefully inspect the carbon resistor to make sure it's touching at both ends where the contact metal prongs are located. You can gently bend those prongs. DO NOT BREAK THAT RESISTOR as there are no aftermarket replacements. You can also drag a piece of 600 grit emery paper across the points inside the unit but be very careful not to break any wires. Reinstall sending unit and see if it works any better.

2. If above doesn't help, remove sending unit again, clamp it gently in a vise so as not to crush anything and remove the top of the unit using a brake spoon adjuster or a flat blade screwdriver resting on a small fulcrum. Pry up a little at a time all round the top where the dimples are and the top will pop off. You will see what's shown below.

3. With the unit still in the vise, use a very small flat blade screwdriver (carefully placed) so that you can rest one edge of the screwdriver against the inside of the case and the other edge inside the star wheel tooth, and turn the little star wheel adjusting screw. It does not turn easily. You can tap the screw driver VERY GENTLY with a small hammer to make it move. THE SLIGHTEST MOVEMENT WILL EFFECT THE GAUGE READING so tread lightly.

Turning the star wheel just a teeny, weeny amount will affect the gauge reading. Turning it CW will make the gauge needle read closer to FULL. Turning it CCW will cause it to read closer to EMPTY. BEFORE you make any star wheel adjustment make alignment marks so you know where the star wheel was located when you began.

4. Each time, after you adjust the star wheel, move the float arm thru its range of motion while it is lying on the rubber trunk mat or a big piece of cardboard and connected to the hot wire from the gauge and also grounded to the trunk floor latch. Use alligator clipped wires and don't let any wires touch each other. Check your gauge reading to see if it correlates to the motion of the float arm. This is a very tedious and time consuming process and you must have the patience of a toothache.

5. You may also find that you may have to also bend the float arm slightly during this process.

It took me many hours over several days to realize how the movement of the float arm and the adjustment of the star wheel all delicately interrelate. Don't rush the process. I always say that if others have done this, so can I at least try. Pretend you are an instrument maker or a fine watch maker or a gemologist working on the Hope diamond.

When you finally get the sending unit and the gauge to read sensibly, fill your tank with gas and then visually and mathematically calculate how much gas is left in your tank when the gauge reads F, 3/4,1/2 1/4 and E. Hope this helps. Didn't intend to make it so long but,I wanted to include as much detail as possible to alleviate guessing and assure success.
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[whb52ford]

Thanks for the very detailed messages. Today I filled the tank. Went to 3/4 and stayed there. Drove 45 min. Got back in car and gauge went to full and stayed at full all the way home.

Question: I found one from a station wagon. Top looks the same but arm is different. Can the arm to float be changed or is that a big deal?

[Drbrown]

I'd say try it and (1) see if it slides into tank, (2) see if do screw holes line up, (3) measure depth of your tank and outside of the tank, move float arm up and down and see how it compares to tank depth, (4) if the amount of arm travel looks similar then note how full the tank is and temporarily install the sender unit, (5) turn ignition on and see if the gauge reads at approximately where it should based on amount of gas in tank. From this point you could possibly bend the float arm to fine-tune the gauge reading.

When you do a final install, be sure to use a sealing compound that states it is gas resistant.

[19Fordy]

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I agree with Drbrown. Float arm is easy to bend. Just be patient. I would not try to remove and inter change the float arms as you will probably damage the unit mechanism.

[rotorwrench]

I learned a long time ago to first check all internal connections for condition and security prior to any readjustments. Where possible, connections should be cleaned. Now this is a general statement but it works for a lot of electrical assemblies. In this assembly, the tiny little points on the bimetallic switch can get crusty. They can be cleaned using light grade sand paper like 400 grit wet or dry with regular paper strips & compressed air to clear away debris after. This operation takes a while and care has to be taken not to damage the unit parts in any way. The rapid opening and closing of these points is what controls the pulsed current flow to the indicator gauge in the panel. This is generally all that is needed besides the good grounding and other electrical connections mentioned here and elsewhere. Adjustments can be performed after this if necessary.

[19Fordy]

That fuel tank sending wiring is so delicate I would only administer air by blowing (with your mouth) thru a straw. The straw can be paper or plastic!

[whb52ford]

Since I now have detail instructions on taking the cap off, I think I will try that and see exactly what is going on in there. I should have taken a pic of the sending unit when it was out so I can be on the lookout for one close to mine.

I learned a lot and thank you for the very valuable information.

When I get something to work with, I'll take the tank down again.

[19Fordy]

Does the unit you have from a station wagon look like this one?
https://www.ebay.com/itm/NOS-OEM-For...wAAOSwEJ1cCukY
If it does,try bending your float arm as mentioned earlier. I bet it will work. If you have a spare fuel gauge you can also easily test it as shown below. 2nd photo shows underside of unit and how float arm is attached. I would not recommend trying to separate the float arm from the unit.You will destroy it and the unit. If you really need to make the arm shorter, you could cut it and solder it in place. Look closely and you will also see 2 little metal tabs that can be slightly bent to adjust the movement arc of the float arm. Bending them a little greatly changes range of float movement and can be used to adjust the unit. These are not meant to be bent many times as they will snap off. Be judicious.