What is wrong with my car fuel system (only getting 1/2 tank)?

1984 Toyota Corolla 4-AC engine FWD 4 door.

Mechanical fuel pump, no electric in-tank pump.



I've been trying to fix this problem on my own and I'm running out of ideas. I need to drive it 400 miles from So Cal to Northern Nevada.



Symptoms:

Car stalls and engine stops after between 160-190 miles (about 1/2 tank). The way it quits is definitely a lack of fuel being delivered. When I put some more gas in (even a little, like 1/2 gallon) it will start and run again, but not until it has more fuel.



When I fill the tank again after a stop it is always about 7 gallons +/- (including station gas and from my emergency canister). Again, this represents about 1/2 tank.



History:

This problem has been persistant for 2-3 month or more. A few weeks ago I discovered a fuel leak on the gas tank and had it repaired. I don't believe that the leak has returned or that there is another, but anything can happen. I haven't seen any more evidence of leakage.



Fuel pump was replaced a week ago, hoping that it was a "weak" fuel pump.



The problem persists and last night I looked at the fuel parts in engine compartment and noticed that according to the diagram the fuel supply (to pump) and fuel return lines were switched. Switched them and drove some more, but engine still gave out at 174 miles.



I looked at the fuel pump some more and tested it a bit. It turns out that the actual fuel pump (replaced recently) draws fuel from the top and returns it from the bottom. This is opposite from the diagram in the Haynes manual.



Next I tested the fuel lines from the fuel pump. I ran it out of gas (well, 1/2 tank) and put some in and drove it home. I blew down the fuel line which had been connected to the fuel filter and it did not produce any bubbles in the tank. I blew down the fuel line and it DID make bubbles in the tank.



So I tried switching the return line onto the fuel supply input of the fuel pump and it ran fine that way. But it didn't run with the line that is supposed to be the fuel line connected to the input. Well it seems like it's possible that I switched up the lines badly when I re-installed the tank. I labeled everything and I could swear that I hooked it up correctly.



I siphoned about 2 gallons out of the tank (which is about how much I had put in when it stopped) and now neither lines make bubbles in the tank. (The fuel return or fuel supply line.) The car won't run, but I know there is still gas in the tank. At least 4 gallons, which it used to be able to run on just fine.



Please help I'm out of ideas and ned to be there by the 15th.What is wrong with my car fuel system (only getting 1/2 tank)?
The fuel line might have deteriorated in the tank, and now it is not long enough to siphon fuel from the bottom of the tank up.



Is it the original line from 1984?What is wrong with my car fuel system (only getting 1/2 tank)?
Here's my theory: You obviously must have a fuel level sensor in the fuel tank, right? I'm thinking when that arm with its float gets to about the 1/2 fuel level mark, the arm is pinching off a rubber hose that feeds fuel to up to the front of the car to the engine. You've done a pretty good job of checking everything else. I'm not clear on if you had the tank out to inspect that portion of it yet, based on what you wrote. Since the problem occurs only when you reach 1/2 tank of fuel, that tells me you need to check out the fuel level sender in the tank, since it seems to be an obvious correlation. If you haven't checked it out, might want to drop the tank and look inside there to see what you can see. Hope this helps.