I have a 92 F150 w/dual tanks, the front tank sender (or gauge) gave me various readings, or lately, always reads empty on a full tank.
I popped off the cluster cover and started taking resistance measurements, at the fuel selector switch..FSS, my first plan was to look for broken wires or missing grounds.
On a 92 F-series 6 pin fuel selector switch pin 5 (yellow/white) is the output to the cluster fuel gauge. If one tank always reads the correct amount then this circuit is probably OK, as is my case.
Pin 4 (Dark Blue/yellow) is the input from the front tank sender.
Pin 6 (Yellow/ light blue) is the input from the rear tank sender.

First of all, I removed the wiring connector from the FSS, this enabled me to get resistance readings from the tank senders without any voltage on the wires. Both tanks were topped off at the time I took these readings:
Front tank sender was 16 ohms
rear tank sender was 160 ohms
I happen to have a brand new Ford sender, I took readings from it on the bench, it has a resistance range of 16 ohms to 160 ohms.
As I looked at the new sender, specifically the float ball, it dawned on me exactly what is wrong. The sender uses a very thin gauge brass float and I believe it has started leaking. I have been having problems with lawnmower floats lately, they are made of two brass sections and are soldered together with some kind of lead/tin solder. The lawnmower floats are made of extremely thin gauge brass and were developing tiny pin-hole leaks, filling up with fuel and sinking, rendering the carburator completely flooded.


Then it hit me!!! There is nothing wrong with my sender electrical circuit, it is working, the float in the front tank has sunk to the bottom and is reading 16 ohms just as it should be when the tank is empty. There is a leak in my sender float, it is full of fuel and sinks.
I have noticed that if the front tank has been empty for a while, the gas gauge works for a few hours after I fill it back up. While the tank is empty the float slowly drains out, and initially works when the tank is topped off. The next day my front gauge reads empty again because the float fills up and sinks back down.

I will post a confirmation as soon as I can get the old sender out of the tank.

PS: I am sure most of you already knew this, so don't pick on me for repeating the same old stuff.

 

I actually never thought of that. You're right about lawn mower carbs doin that lol. I hate those things. Good chance that that float is fillin up. Great advice 924.

 

One more point, I may have missed and wanted to stress: The short-lived lawnmower carb floats are constructed with the same technique and material as the Ford sender float; they look identical except for the size and shape.
Also, I was thinking the Ford float could be repaired if you knew how to braze or solder well enuf to patch a pin-hole leak or weld fracture.
I have seen both pin-holes and seam fractures in the carb floats.

 

Have you been driving my truck? You described its symptoms perfectly... I just bought it so I haven't had a chance to think about it, but I won't be surprised if I needs me a float!

Thanks!

 

You're absolutely correct - in every Ford I've had with dual tanks, the front sender always stops working first. When I did the pumps in my last truck, the float in the front tank was made of plastic, and the plastic was worn all the way through where the float arm held it.

In my 1991, guess what, the front tank never reads. I'm 100% sure it's the float and not the sender. When the pumps start to go, I'll be replacing that little float with something that can't ever leak, something analagous to styrofoam and water. Now I just need to figure out what won't dissolve in gasoline over the course of several years.

 

In the old days I remember carb floats made of some kind of cork or wood. Is that any good? Is it too expensive, better or worse than a sealed brass ball.

AndyM, what truck did you have plastic floats in? I wonder if mine is plastic also? The replacement I have on the bench is brass, but I assumed my tanks had brass floats cause the Ford replacement was brass.

I wonder what stresses out the floats more...the back and forth, or random wave motion of the fuel, or maybe the vibrations from rough roads when your fuel tank is empty

 

That was a 1990. I remember noticing that the two floats were made of different material.

I'd bet the biggest source of stress would be the fuel splashing them around.

 

hmmm... braze a brass ball with residual fuel in it....

Where's the popcorn.... I gotta see this!

 

924 - I won't make fun of you, no worries. The float is either plastic or brass, more likely brass. Easy to solder, but difficult to get the fuel out of it, which is why it sunk in the first place.

years ago I put the effort into doing this... I found the leak and enlarged the pinhole with a small drill bit, then did the same on the other side, and got all the gas out I could. Then I put it in the sun for the day. THe next morning I sanded the area around the two holes, and soldered them closed with plumbing solder, and a 100W soldering iron. It floated fine from that point over.

When the floats went bad in my 93 crewcab, I just replaced the whole float assembly. For $20 or so I couldn't be bothered drilling, sanding, soldering.

The trick to fixing these floats, is to enlarge the hole a little bit, then solder.

 

Sofla David, it isn't a good idea to apply heat to a container of gasoline. But you must remember this little fact about me...When I was 10 years old we made a bomb. I drilled a 3/4 inch diameter hole about 2 inches deep into a piece of wood, filled it with gunpowder, then capped the end with some kind of plug. Our problem turned out to be lack of a fuse, in order to install the fuse, I decided we should put a small hole into the side of the big firecracker. I started tapping a nail into the side of the bomb and.....the rest is history, I'm lucky that I can see and hear normally today, I was very close to losing a hand or eye...but that incident never discouraged me. I think we went cliff diving at the quarry the next day.

 

COOL!!! LOL

worst I ever did was when I was cutting a trailer in half. It was sheet metal with a (very rotted) plywood core.... After some cutting with the grinding wheel, the wood started smoking... then the Flames started!!!!!

I sat back and watched it burn for a little bit, then called my 7 year old over with the hose to play "Fireman"... He thought it was the coolest thing in the world... he got to put out a REAL Fire!.

 

If you drill the pin hole larger, and another hole on the opposite side/end, and sit it in the sun, it will be solderable the next morning.

I wouldn't use a torch on it, but a soldering iron, no problem. Done it before with no problems.

 

What solder? Rosin core or plumbers acid core? 60/40?

 

The sender is out and I have found out why my float leaked!! There was nothing wrong with the construction of the float, the side welds were good.

The problem is what the float was hitting every time the tank was full. I removed the pump/sender assy, and observed a dent in the float, the float was covered in varnish from years of submersion in fuel, except one corner, it was shiny and dented as if it had been banging against something.
I moved the float back and forth while it was still attached to the pump and discovered that when the sender was in the up or full position the corner of the float was touching a metal line that is part of the internal pump.
The new sender I bought from Ford also did this. I fixed the problem by bending the float arm just a few degrees, the arm is metal rod about 8 inches long with almost a 90 degree angle about mid-length. I had to increase the angle just a few degrees so that when the arm and float were in the full position the float was about 3/8's of an inch from the metal line it used to contact.
Before installing a Fuel sender make sure the sender moves back and forth without contacting the pump assy. The float needs to move freely in the tank also. The float can be installed onto the sender arm two ways. One way is with the majority of the float body away from the sender, this is no good because the float will bump into the side of the tank. If you pull a new sender out of the box make sure your float body is closest to the sender and not touching the pump at any point .There is a groove around one end of the float and the arm rod loops around it, the float can be removed and switched so that the majority of the float is in close to the pump. Do not bang the arm while installing the assy, either. The float is the first thing that is fed thru the gas tank hole when installing the sender/pump assy. It is easy to bend the float arm, and cause yourself more trouble.

I filled up my front tank today and the front gauge is reading exactly on the "F" mark.
I am glad I stopped going to Bill Marsh Ford , this was their handy work, they replaced the sender 8 years ago( under warranty), and it failed in less than 3 months. I hate all Ford Service Departments , I never had anything fixed correctly by any of them. If you want anything done right DIY!!!

 

Plumber;s solder, acide core. Electronic solder will last about 3 days submerged in gasoline.

Ask me how I know that ;-)