Can I test fuel sender unit on my 53 Merc?

Britcheflee · May 5, 2013

The fuel gauge on my old car has a life of its own - goes up and down randomly and seems to show 3/4 full even if full or half - there is easy access to the top of the sender unit in the trunk - there is a single connector from what I see with what also appears to be a little device which looks like a capacitor or something.
A new sender unit complete is not that expensive - before ordering though is there a way to test if it is working or not? if I completely disconnect should it show empty and if the wires are connected should it show full?
6 volt system.
Thanks,

Lee

Texas! · May 5, 2013

I don"t know about 1953 but on my 1958 F600 if I remove the wire to the sending unit and connect it directly to ground (12V Neg ground electrical system) the gauge goes to Full.

frrankmn · May 5, 2013

I believe the float arm is attached to a variable resistor. If you take it out and check it with your ohm meter you may find the problem area on the resistor. You may not be able to fix it but it will be educational.

Britcheflee · May 5, 2013

OK thanks - the gauge goes up and down randomly even when at rest so the fuel is not sloshing around - thankfully it looks like a pretty simple job to remove and, for once easy access through a top plate you lift up.
Have to double check I have the battery disconnected before I mess with that!!!!
Lee

Den N Ms · May 5, 2013

Britcheflee Chances are the tank is loosing ground to the chassis causing the gauge fluctuation.To check your gauge with sender wire disconnected it should show empty,and with the wire grounded to the chassis it will show full.Try running a ground wire from one from one of the sender attaching screws to the tank the frame.

JMOR · May 5, 2013

(quoted from post at 14:13:59 05/05/13) Britcheflee Chances are the tank is loosing ground to the chassis causing the gauge fluctuation.To check your gauge with sender wire disconnected it should show empty,and with the wire grounded to the chassis it will show full.Try running a ground wire from one from one of the sender attaching screws to the tank the frame.

guess Ford & Chevy just had to do things differently, once again!!! My 1962 Chevy PU is around 0 to 5 Ohms empty and ~ 40 to 50 Ohms full. Mo Ohms = mo gas.

And when key off it goes to empty.

Britcheflee · May 5, 2013

OK that's very useful - will give that a go this afternoon.

ZANE · May 5, 2013

On my 51 Ford sedan the gas gauge stopped working some years ago and I had to run a wire from one of the sender screws to a good chassis ground on the frame.

That fixed it.

Zane

Anonymous-0 · May 5, 2013

That little device you mention is a static suppressor for the
radio. Check your gauge by grounding the wire, if it goes to full
gauge is good. You can buy a new sending unit from one of
the many aftermarket suppliers. Nice thing about old ford
products. I own 8 of them from 46 - 62.

Cliff(VA) · May 7, 2013

I had a similar problem with another vehicle. I removed the sender from the tank and inspected. It was full of goop. Used carb cleaner and light soft brushing on the winding part of the variable resistor. Fixed the problem completely. Problem was still gone when I sold the car several years later.

I would try grounding as suggested below first.

Cliff(VA)

PS It looks pretty bad when you design automotive instruments and senders for a living and your fuel gauge doesn't work.

Britcheflee · May 7, 2013

I disconnected it and the two tabs which go to the top of the sender unit were very badly tarnished - once disconnected the fuel gauge stayed at E once cleaned up and re-connected the gauge went to just below F - looked inside the tank filler and the tank is full to the top - going to drive it around a while to get the fuel level down and see if it changes the needle position - it appears to have stopped the up and down movement now the connectors have been cleaned.
The two tabs were not separated by anything like a spacer - I assume it is ok for the two wires to be contacting like that? I would assume that if they are touching it is going to show full no matter what?
Two days of fairly heavy welcome rain here cleared out all the pollen and dust thank god.

Lee

Cliff(VA) · May 7, 2013

I am not quite sure what you are describing to me.

Normally there are two types of fuel senders: one with one terminal that gets the circuit return through the body of the vehicle and one with two terminals that has a wire both for the gauge and the ground return.

If your sender is a two wire type and the two terminals are shorted, you will get a F indication.

What I would do is use an ohm meter to read the resistance between the two terminals OR the one terminal and ground and move the pointer. If the resistance changes smoothly with no sudden changes the sender is probably good. If it swings back and forth suddenly, I would try and clean the sensor reostat.

Good luck!

Cliff(VA)

Britcheflee · May 7, 2013

I will send a pic if possible but pouring with rain at moment.

this one has a single connection right in the middle at the top - there is one wire which comes from somewhere from the rear of the car (which I tested and supplies power) with a round tab on it and one which goes from the connection via that suppressor and is connected to one of the screws which hold the sender in place (so I assume grounded) - both wires were connected to the middle of the sender by a single screw with no spacer in between - for some reason I cant see how this could work as surely there needs to be a spacer between the two so they don't contact and just ground out? Maybe that is why the gauge reads full all the time?

Cliff(VA) · May 8, 2013

Based on the picture you posted elsewhere, you have a "one wire" fuel sender.

The wire feed going to the meter supplies power (excitation) as well as providing a signal to the meter. The other lead to the "suppressor" filters the sender so that the gauge does not bounce around alot.

I think your problem is with all the rust on the tank. It is not getting good ground connection back to vehicle ground. My suggestion is to pull one of the screws that holds the sender in the tank. Clean it "clean bright and tight. Slip a wire with a ring terminal under it before you replace it. The other end of the wire should go to somewhere on the frame of the vehicle with a "clean, bright, and tight" connection.

If that does not fix it for you, I would remove the sender from the tank and try the proceedure I outlined above.

If you need more help my cell is five four zero, three three six, three two seven four.

Cliff(VA)

Can I test fuel sender unit on my 53 Merc?

Britcheflee

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