Gas 5.4 or v-10 question on gauges 2003 era

[path1]

Not normal for mine, at least never did it before that I noticed.
Started engine today and dash light came on. The light that looks like a gas pump, indicating I'm low on gas. Then over a mile driving the light went out as gas gauge slowly raised to about the level I had in fuel tank (1/2). This is in small class C that hasn't been used much last couple years. But once a month I take it out to splash fluids around.

Going to test tomorrow with volt meter to see how much is back feeding thru alternator if any. (My cruise control does speed up 1 or 2 mph over a long stretch of road, classic sign of unregulated elec back feeding thru system. IE...shot diodes in alt. That is if ford even has replaceable diodes for these alts.) Gas is about year old but is treated with fuel stabilizer.

What do you think?

Gas is to old, even though it is treated?

Sending unit in tank sluggish a bit from non use or going out?

How long does it take for you fuel gauge to registar when you start yours, if you have same era of Ford?

Something else I'm missing?

Thanks

[Grit_dog]

Has nothing to do with old gas.
Not worth digging into imo on a 15 year old truck, but probebaly the fuel sender?
If you need things to work on, come on over. I got plenty of electrical or mechanics projects to keep u busy!

[bartlettj]

All gauges have some damping built in so the gauge doesn't flail around as the fuel sloshes. If you are worried about the alternator diodes, check the voltage and state of the batteries.

[MetalGator]

My truck will do this sometimes if I don't fill the tank to full. I almost always completely fill my tank when fueling but a few times I have just put in 5-10 gallons and my fuel gauge will read the same as before I put in fuel. It usually takes a few miles of driving for it to register correctly.

[dodge_guy]

My 01 Explorer does that occasionally. has a new fuel pump/sending unit in it. it reads normal. So I just live with it.

[MitchF150]

Yes, I think even my 97 F150's owners manual says to not have the engine running or the key on while filling the gas tank or the gas gauge will not register properly..

[time2roll]

My 2001 F150 registers the gasoline level immediately. I believe all dash indicator lights come on at some point as the truck starts to demonstrate all is working.

Ok but this is odd. Some years back I filled the truck in Las Vegas with the engine running because it was very hot. The fill up did not fully register for 50 or 100 miles. These gauges are controlled by the computer and I believe the computer must reset when the vehicle is turned off as it relates to the fuel gauge. This day it took about an hour to register and made me question if I really had it full as I headed north on highway 93 where gas was scarce 17 years ago.

Definitely check the start battery voltage before and after you start the vehicle to verify alternator function.

You could try filling the tank (engine off) and see if the level indicator improves. Otherwise I think you are looking at a new fuel level sending unit. I don't know the diagnostic on this item. If you take it into the shop they will appreciate if it is low on fuel.

[MitchF150]

Most gas tanks, even new ones, still use a physical "float" to measure the level of gas in the tank.

Having one sit for awhile, it could stick for a bit..

Even on my 13 F150, if I have about a 1/4 tank of gas left in the tank (36 gallon tank) and park with the truck nose down for any length of time, my low fuel light will come on..

Once I park on level or nose high, the light goes out and the level on the gauge rises again.

Even going up or down long grades will change the gauge and the "Miles to Empty" reading on the dash...

Good luck!

Mitch