You might want to run it down to E (keeping a can of gas with you) and refill to see if it even goes to E. Could be a sticky float, misadjusted, or the instrument regulator putting out a higher voltage, etc.

Pull the sender unit out and test it?(You can test gauge reading vs float stroke fairly easy assuming your bolts come out easily UNLIKE MINE which required vice grips on two)

 

A bit off topic, but I got bit by a fuel cap once. The car was fine for a couple of months after putting on the cap but I took another job which required me to drive around quite a bit in Oklahoma summer heat. I'd go run a call and come out to find the car seriously flooded. The next time I'd come out and have to crank the daylights out of it before I'd get any fuel into the carburetor.
At first I thought it was vapor locking. I had clothes pins clipped all over the fuel line. I even rerouted it but just couldn't figure it out.

The penny dropped when I forgot to get gas one morning. Normally I'd get gas at the Sunoco station about 1/2 a mile from my apartment. I went straight to school. That afternoon was particularly hot. I had gone about 20 miles when I decided I'd better stop for gas.

I got out, put my key in the locking cap, turned it and FWOOMP! The cap and my keys blew right out of my hand landing about 20 feet away. I'm sure I stood there like a cow staring at a new gate for a while. Then it dawned on me what was happening. .

The new locking cap had a gasket on it. I dug around in the trunk and sure enough tthe factory cap didn't.

If I drove it just far enough for the heat from the engine and fancy new exhaust I'd had put on it, warmed up the gas tank it would build pressure. It was ok as long as I was driving it, but if I turned the car off, the pressure was too much for the needle valve in the carb. It would leak past and flood the motor.

If I drove it far enough to use a decent amount of gas it would draw a vacuum on the tank as it cooled and suck the fuel all the way back to the tank as it cooled.

I hacked the gasket off the cap right there at the gas station.

Problem solved.

 

Not off topic at all Hillbilly...and interesting info. I am going to keep an eye on this now that I have read this. But my previous gas cap had an gasket (looked tired and cracked) and the new one does too. I guess we will see!

Thanks!

 

The vented gas cap has a gasket to keep gas sloshing out. You should see a small hole on back of vented cap.
Actually, I looked at my old cap. It has two holes near the tabs that holds it on the filler tube. They connect to four holes around outer edge. I'm going to try this cap on mine. I have been using a pretty chrome cap I think was on donor cap. I see no holes in it but was able to blow through it on a filler tube. Maybe old cap would vent better. I have had a lot of carburetor issues so who knows.

 

This is the vented gas cap i have from LMC.
There is a little one way valve in the center to let air in and it has a spring that pressure has to overcome to escape when there is tank pressure.


Valve in middle

Rubber seals against filler and to the gold backing plate but allows ventilation to pass between the gold backing plate and silver back side of the cap

 

My chrome cap is different. It has a spring but no center hole. Apparently, with cap screwed down the vent opens. I can put it on an extra filler tube and hear sir blowing out with cap tight.

 

My new cap looks exactly like the one Dennis has. And seems to have solved the issue I was having.

Next on the list is to figure out the float issue!

Thanks all!!

 

Read through Red60's F250 saga. Use the way back nachine. Around post 120 and the resistor around 140. He is very detailed about all his repairs. I think you will find a lot of items of interest.

 

So before i did the gas tank swap (from behind the cab to under the bed) I had similar issues with gas gauge not reading correctly. One thing I found out is that when you replace the sending unit, Although I thought I was putting a stock unit in, turned out that the reading was incorrect. Ford use 73 - 10 ohm resistance for their tank/gauge pre ‘85. I found a resistance substitution box on amazon and checked my gauge... it was still working, then i checked the sending unit and it was way off... so apparently they sell original replacement sending units with generic ohms like 240-33. Once i replaced the tank and used the correct 69 mustang stock sending unit at 73-10ohm, the gauge read fine... (I also ended up using modern gauges with fuel set at 73-10ohm).

The resistance substitution box was like $34.00 which takes all the guess work out of what is sending what to where.