sleepydog

First post! Great sight btw... My new to me 2004 F150 STX - the gas guage recently went to empty, even though tank was 3/4 full. I toppped off tank and after a couple of trips it was acting normal again. Today I run out at lunch and notice it is at empty again. I filled it up again, and it only went to 3/4 full. Now when I turn it off the gauage pegs at Full (I mean way beyond full). When I start it up, the gauge goes to 3/4 full. Based on my searching it appears to be a ground issue - Where do I look for common wear points?

Any help is appreciated.

alsatropine

iTrader: (2)

Might be the fuel sending unit which is attached to the fuel pump inside the tank. Had an issue with this on another vehicle I owned. Trash gets in there and causes the unit to send faulty readings.

Mod (Ret.)

This may sound strange, but it may be the battery. Have it load tested.

kanga2311

I had this happen to me about a year ago. Got in the truck, saw I was almost out of gas, even though I just filled it a few days before. I thought I had a serious problem, truck getting really thirsty, leaky fuel line, until I filled up again and only got 3 gallons. I didn't really have time to figure it out, just kept track of mileage to make sure I didn't run out of fuel. Sometimes it would jump to where it should be, then back down to empty. Then it just started working again and I haven't had a problem since.

sleepydog

An update - the gauge fluctuation got even more bizarre, as it seemd to rotate itself 90 degrees clockwise (i.e. it was pointing down into the battery gauge for "full", and returning to the "F" mark of the fuel gauge when power was turned off... Go figure.

In my research I saw a post somewhere to try a can of fuel system cleaner through the tank - comment was that sulphur buildup on the sending unit would cause it to create faulty/erratic signals to the gauge. I poured a can into the tank and have run it for a day - when I got out of work and started it up to drive home, the gauge was reset to the correct orientation and appears to be functioning normally. Worked fine on the way to work this morning. Time will tell.

Thanks for the input.