Fuel gauge malfunction

So, over the past four years of owning my truck, I have had a few fuel guage anomolies. Maybe 2 or three. Usually consisting of me filling up at a half tank(like i always do cause i still havent got around to doing the in-tank fuel mod) and the guage doesnt go back up to full. It takes an hour or so to be where it should be. Well, i fill up a couple weeks ago, and it did again. This was the first time i had seen it do it in a year or so, so i thought no big deal. Well, on the next fillup last night. Again. I get in the truck this morning and its on E and the low fuel indicator is on, which ive never even seen.

Any suggestions? Guessin maybe its time to pull my tank and check things out inside? And while im at it, do the in-tank mod?

Maybe a grounding issue? Or even a fuse?

I know mine likes to say I have less fuel then I really have going down hill and more fuel then I do have going up hill.

Travis

Tman, i know exactly what youre talking about as far as how it reacts to the incline or decline. Where would i check for a loose ground at?

You should have a cable, could be an uninsulated cable, from the engine to the body of the truck somewhere. It really screws things up if it is loose or damaged.
Jim

Jimmydee, i was asking if there was a more specific ground that i was not aware of. I will check my main ground just for safe measures though. Thanks.

The cable that runs back to the tank from the front of the truck has a (sort of flimsy) connector near the tank. When you drop the tank, you need to disconnect the line there. I noted last winter that mine was fouled up and not a very tight connection so I cleaned it real good. It is pretty hard to reach in there however w/o first undoing the tank attach bands (4 bolts) and lowering the tank some. And if you do all that, you might as well test the sending unit...it could just be going south on you which would explain the incorrect level indication and the 'out of fuel' light going on. Some folks claim you can reach in there and disconnect it, but I cannot do it.

On my 2002 F250, the sending unit voltage signal is the yellow wire with white stripe. Supposed to be the same for yours...

Here are some sending unit readings I took while diagnosing a problem with my aux tank controller. (These were taken in the cab, using a long wire that had been spliced into the sending unit very close to the connector at the top of the tank). I don't know if these are "normal" or not, they're what I have (?):

Gauge reading / Voltage measured
Completely Full: 3.25V

My truck showed no fuel about a week ago when it was about 35 outside. I jumped in the car and drove it.
Got back home it was 55 outside and everything worked great, hasn't done it any more.
Doug

Thanks for the info guys. very informative! It hasnt done it since, but next time it does, and if it continues to be an issue, I'll know where to start. Thanks again.