Fule gauge quit working

[38plymouth]

I took my p6 for a drive last night and the needle on the fuel gauge only jumped to just barely past the empty line when I started it. In the past the needle would move around alot between how much fuel was in the tank and empty. It would always eventually jump back to the right spot while driving. I figured I was almost out of gas so I went to fill it up and it only took 5 gallons. The needle will only jump just past the empty line when I turn the key. I looked at the back of the gauge and the 2 wires are really clean and tight. I won't have time to look into it further until the weekend. Does anyone have any suggestions on what to check first? I hope it's not the sender, I really don't feel like pulling the tank out.

Edited July 27, 2011 by 38plymouth

[Robert Horne]

I pulled the fuel sender out of my 37 tank. The fuel sender would not react very good with an ohm reader. I cleaned the sender contact and the small coil of wire with a soft tooth brush, and a little baking soda/water.

Carb cleaner may a good way to clean also. Fuel varnish builds up on the contact and the coil of wire. Often, just cleaning the wire connection on the sender may let it work correct.

[Robert Horne]

You can pull the sender out without pulling the tank. There is an access lid over the fuel sender unit. Your float may need replaced also.

[38plymouth]

Is there access through the truck floor?

[TodFitch]

You can pull the sender out without pulling the tank. There is an access lid over the fuel sender unit. Your float may need replaced also.

When did they start putting an access hole over the sending unit? My 33 PD does not have that which makes dealing with the fuel sending unit a real PITA.

[Robert Horne]

My 37s and 38s have easy access.

[greg g]

did you try to ground the gauge to the body of the car? or is there some interference with something under the dash? My defroster duct dropped of the difusser, and the wire stiffening coil provided an indadvertant ground when it contacted one of the terminals on the gauge. This made it read full all the time.

[Young Ed]

When did they start putting an access hole over the sending unit? My 33 PD does not have that which makes dealing with the fuel sending unit a real PITA.

My 46 pickup doesn't have one but it was a running change right near the end of the cab design. Although the WC style of truck died after 47 the cab went on with the powerwagon so maybe thats why. My 48 plymouth does have the hole in the trunk.

[38plymouth]

I looked in the trunk last night and found an access cover, I was very happy until I removed the cover to find that half of the sender is covered by the trunk floor so I can't get one sender screw out and the sender won't come out. Back when I had my dual exhaust built the idiot that did the job built it the way he wanted and not the way I wanted. His way included moving the gas tank towards the passenger side of the car so he could fit the pipes between the frame and the tank. That also means that it moved the sender out from under the access hole. I'm going to have to unbolt the rear exhaust pipes and hope they will move enough to slide the tank alittle. I don't see it working because there is almost no room between the pipes and the frame and tank. I now have another reason why I should have strangled the guy for building the exhaust his way. I did try grounding the tank to the frame and that didn't do anything. I also checked voltage across the gauge terminals and I had a little over 2 volts.

[greg g]

even if you oly have partial access you could try to see if a ground wire might work. just jumper from the one screw you ave availab el to the trunk floor and see if it makes a dfference in you gauge reading.

[38plymouth]

even if you oly have partial access you could try to see if a ground wire might work. just jumper from the one screw you ave availab el to the trunk floor and see if it makes a dfference in you gauge reading.

I tried that, I wish I could say that it worked.

[Robert Horne]

I was looking at the reading I had wrote down for the 37 sender, 10 ohm to 32 ohm,,,,,,,and my 38 sender, 11 ohm to 50 ohm. My Mustang sender, (new), 0 ohm to 50 ohm. The high ohm reading are full, and the low ohm reading are empty. My ohm reader is not very accurate.

[LAKOTA169]

When did they start putting an access hole over the sending unit? My 33 PD does not have that which makes dealing with the fuel sending unit a real PITA.

My '37 coupe doesn't have one.

[38plymouth]

I got my sender out and tested it and it works great. The problem is that the cork float isn't floating enough to raise the arm. They seemed to be soaked with gas. I took them off and grabbed a wine bottle cork and stuck that on the arm and it works really well. I think the plain cork will soak up gas though. I might try a synthetic wine cork. Does anyone have any ideas on how to fix this without buying a new sender? Is there a gas resistant coating I could use on a new cork?

[Desotodav]

I have spoken with numerous older car enthusiasts here and have been told stories of using shellac flakes (bugs wings) mixed with methylated spirits to provide a long-lasting sealant to gas tank corks for sender units. It sounds like one of those old farm tales, but it would appear that it was a common practice in the old days and was proven to work.

Desotodav

[TodFitch]

I have spoken with numerous older car enthusiasts here and have been told stories of using shellac flakes (bugs wings) mixed with methylated spirits to provide a long-lasting sealant to gas tank corks for sender units. It sounds like one of those old farm tales, but it would appear that it was a common practice in the old days and was proven to work.

Desotodav

"Was" is, I think, the operative term. Shellac is attached by ethanol. So while a shellac coated cork float was a standard and durable way of doing things in the old days it is probably not what you want to do now.

If it were mine, I'd buy a cheap universal sending unit and transplant the float to my original sender. The theory being that modern floats, whatever they use nowadays, should be resistant to issues in modern gas.

[Young Ed]

Yup head to a car parts store or a salvage yard and try to find a float. Even stop by a couple repair places and see if they are doing any fuel pump replacements. My p15 has the old float off my 94 dakota sendign unit. Been working great for years. FYI if you do buy a repo sending unit it will most likely have a plastic float anyways. The one I bought for my 46 pickup does.

[38plymouth]

I'm thinking that I would like to try the float in this thread...

http://www.gudim.com/ReplacingCorkFloats.html

Is there any reason why I couldn't drill a small hole in each end of the float so I could slide it on the arm like the original cork? I would then solder the holes shut tight to the arm so it doesn't leak.

[38plymouth]

I just ordered one of these from Ford, it cost $14.49 and they had 42 in the warehouse. I figure for that price it will be worth a try even if it doesn't work.

[greg g]

wonder how the synthetic wine cork will hold up to ethanol?? Might have to soak one in jar of gas and see.

[55 Fargo]

wonder how the synthetic wine cork will hold up to ethanol?? Might have to soak one in jar of gas and see.

Well they help up for years when used for various booze bottles, didn't they.

[Young Ed]

IDK I wish I knew of a source for the floats for my dakota sending unit. They are some type of foam and already have a hole down the center for a perfect replacement for the cork. I have had one in my p15 tank for years now.

[38plymouth]

I have looked all over for the modern plastic float. It seems like the only way to find one is to pull one at a junk yard. I don't have the time or desire to do that. I think the brass one will be much better than the old cork style.

[38plymouth]

I put the brass float on last night and it works perfect. The new float is almost exactly the same size as the old cork float. I drilled a very small hole in each end of the float and slipped it onto the wire and then soldered the hole closed over the wire. It took all of 10 minutes to change it and it fits and works perfect now. I would recommend swapping to the brass version if your cork sinks like mine did.