I had problems starting my car cold. Once started I had no issues the rest of the day, and I suspected of a faulty fuel pump. At this point the fuel gauge worked fine.

Last weekend I took a trip and the fuel pump failed at last. I barely got to a small town where a local mechanic confirmed the problem. We were able to get an AC/Delco fuel pump and the problem was solved. I have no more starting issues and completed the trip with no problems at all.

Here's the catch: the fuel gauge is not calibrated. When the mechanic delivered me the truck he told me that the fuel gauge was marking half a tank, but it really only had less than a quarter and that after a filling the tank fuel it would mark correctly. So I filled the tank and the needle went to the "FUEL" letters. I had to take the road again because I was already late. Got to the next town (about 130 miles) and the needle didn't move. Next day I went home (200 more miles) and filled the tank before leaving because I was nervous about much fuel I really had in the tank.

Got home with no issues and this morning going to work I see that needle is indeed moving and now is just a tad right of the Full mark. I'm guessing that I have at least half a tank of gas, and it's marking little more than full.

What can the problem be? The fuel gauge seems to be "working", but is marking wrong. I am 3 hours away from the place where I had the fuel pump replaced so it's almost impossible to get there and get the car checked by this mechanic again.

I'm thinking in disconnecting the battery for a couple of minutes and see if the computer/sensor/whatever resets itself. Will it work?

Thanks in advance!

 

Sounds like the mechanic bent the float arm on the fuel level sending unit when he installed the pump resulting in the inaccurate level reading.

 

Anything I could check, before having to drop the fuel tank?

 

Another thing just occurred to me... If there were something causing a higher than normal resistance in the fuel level sending unit circuit, it could cause the conditions you are experiencing.

This thread is specific to the 98+, but might provide some help to you:
98+ Fuel Gauge Diagnosis

 

I could see someone "bending" the arm of the sending unit if they weren't careful, and would be surprised if its not that other than electrical