While I was diagnosing my failing fuel pump (replaced pump only w/ airtex 3240 Awsome!!), I turned the inertia switch on/off a few times.Then I noticed that the fuel gage was reading empty.While replacing the pump I tested the resistance of the sender and it was smooth from 0 (full) to a little over 1K(empty).Anyway the gage is still pegged on empty, but if i raise(turn off) the inertia swith the gage goes to full. Also i can't rember if it did this before but with the ignition swich in the ON position with the engine not running it goes to full, but as soon as it cranks it immediately goes back to empty(BTW there's half a tank of fuel in it). I feel like flipping that switch caused this and I hate to buy a new sending unit & pump and it not fix the problem. Any ideas on how to further troubleshoot???

 

I've got the exact same problem. I've had the pump out several times to check the sending unit. I'm sure it's an electrical issue, but I can't find any problems. It drives me crazy.

 

I've fixed the problem with the fuel sender / gauge. One of three things done seem to have cured the problem. First, I removed the fuel pump / sender assembly and repositioned it. The feed hoses sit at about one o'clock. I noticed that if i moved the unit before the retaining ring was threaded tight, it would affect the gauge. I'm assuming that the float was fouling the side of the tank. I then made sure that the unit was pushed in far enough to make an audible "snap" when it was in place. Second, I made sure that the threaded retaining ring was really tight, and the access panel cover door was positioned to not hit the sending unit plug. I noticed that if not positioned correctly, the cover would hit the top of the plug and push it down. This was accentuated by over tightening the panel cover when it was being put back on. This cover has a rubber gasket fixed to it that is fairly squashed, on my truck, so it's probably flattened on most older vehicles. Third, I thoroughly cleaned both harness plugs with electrical contact cleaner. This would be the one at the sender as well as the one located in the left hand rear wheel well. The gauge is now accurate, and stays accurate.It may be worth addressing these items when a fuel pump replacement is done. Now, on to the next headache, fuse-able links....