Multiple Questions Interrelated to Fuel Sys

1994 Toyota Camry. Given to me by a friend. I had to have the transmition rebuilt exhaust etc…incl. new gas cap.

Whenever i take the gas cap that i purchased off there is a rush of air into the gas tank. Vacuum in tank.

recently i noticed i was leaking a tiny bit of fuel in the form of drips under the car. It finally warmed up enough this weekend for me to get under the beast to do something about it. Turns out to be what i think is a fuel return line. I made this deduction because when i grabbed a hold of the rubber hose/metal tube connection it broke right off out and gas came spilling out. I had nearly a full take of gas and i scrambled around for containers to hold what would have been at least 10 gals of fuel. By the time i got back to the car the leak had stopped. I spent some time cleaning up the remaining piece of metal tube so that i could get a clamp on it. I was feeling pretty good about the repair 3 hours later when i finally got the hose clamp on. No Leak. This morning i noticed a wet spot under the offending connection that indicated I had not been as successful as i had thought. I took my truck to work. I came home at noon, the sun was shining and car was in a nice sun spot (black car) and there was a steady leak from the repair area. I wondered what would happen if i took the gas cap off. So i did. Leak stopped.


1:do i have an improper gas cap?

2: fuel return: where is the fuel coming from? i.e. returned from what?

clarification: i know the repair is probably sub par: after breaking off the piece of metal tube initially the remaining piece was welded to a lip on the gas tank with no room for hose/clamp. I had to hack saw the weld to free up enough tube to clamp to. Having done so there wasn’t much room to tighten the hose clamp once it was in place, also the flared end of the metal tube came off with the broken piece so the hose fits looser …

The hose you are describing is probably the vent hose for the tank. Follow this hose. It should connect high up on the filler pipe. The fuel return from the fuel pressure regulator enters the tank on top at the bulkhead that supports the fuel pump. The evaporative vapor recovery line is also on the top of the tank. By the way if you truely have a vacuum in the tank the leak would not be evident when you have the vacuum. Also is the Check Engine Light ‘on’?

There should be a vacuum relief valve in the cap. If you look inside the threaded area you should see a circle of holes behind which is rubber. If you apply vacuum and pressure to the threaded part you should be able to draw air but not blow it back. On these Toyotas the cap allows air in. The valving, a solenoid valve, plumbing, and the evaporative canister control and collect the escaping air/vapor.

If you need additional information, check Alldata at your library for a diagram of the evap system; how the ECM checks its operation; and what pressures the system expects.

it’s impossible to follow the hose to it’s end, it does go up though, in the direction of the filler pipe. There is almost definitely a vacuum when i remove the cap. I will cup my hands around the cap next time i take it off. Also, cap off: leak stops at least for the 2 times that i’ve tried this. Alldata? at which library? No check engine light.
it’s an aftermarket cap so perhaps it’s the wrong one…