I have an 85 Toyota pick up efi and I put a new fuel pump in and I cant put the gas cap on tight or it builds pressure and with it off it leaks gas out the overflow in the engine compartment?

Check the 15 amp fuse on your EFI. It's the bottom one close to door post. The fuse tab on mine melted and was not making contact so I cut the wires from the fuse panel and put female ends on them to accept a fuse. Works fine. I've been building these Toyota Pickups with 22R and 22RE for what feels like a 100 years. I even have a new engine I put 125 miles on still on the engine stand here in my garage. Lot's of spare parts too. I've pulled 7 of them apart in the past just to keep one on the road. You can't find them any more.

when you first try getting fuel going. you may have to turn the key on and off a few times to build up pressure. if you can hear the pump working it will change when it builds up pressure. if its not then I would say you have a line leaking. check all your connections before you have a fire

have to clean pipe line which is going from fuel tank to engine

Old post. but this is common on ALL EFI CARS.
great question and is very easy.
btw one of the best posts on the forum best of 1300.
the gas cap must have the proper vacuum breaker (ask STANT for one) if missing the cooling fuel will pull and illegal vacuuum and the gas tank will implode (crush) I have a nice photo of same car doing that.
this vacuum also stalls the fuel pump, as the vacuum builds.
this happens on cooling day not getting hotter day.
to prove this drive with the cap loose and ignore the ECU check light for EVAP failure. (pressure test fails)
loosen the cap key on, 3 times to 5 times to build pump
pressure, the pump only runs key on for 3 sec. then start it up.
the other proof of lost fuel is the test fuel test. (spray)

to google landers. i make this. post.

http://www.matrixowners.com/tsb/T-EG002-06.pdf

this sounds like your problem

Check the EFI main relay, the circuit opening relay, and the fuel pump relay. Inside the fuel pump relay there is a switch controlled by a coil. During start, the fuel pump gets full power for a couple of seconds to build up pressure. Once pressure is good, the fuel pump relay is supposed to switch (via the coil) the fuel pump to reduced power. If the coil in the relay is bad, the reduced power setting is not available and the fuel pump will run at full power all the time. At this heavy current draw, it won't be long until the EFI fuse blows. This would also give more pressure than is necessary to the cold start fuel injector which runs on a timer. This extra pressure during the time that the cold start injector is operating may be the reason the engine is flooding with fuel.

Try replacing your gas cap.
A leaking gas cap will not allow proper pressure to build in the tank

you may need a new gas cap. the cap has to seal up air tight for your fuel pump to build up pressure

remember you are messing with gas.so no fire,sparks and smoking allowed around car.dissconnect neg. on battery.then relieve fuel pressure by taking off gas cap.take all gas out of tank.undo fuel neck,both straps,hoses and any electrical conectors.take take out from under car.remove any dirt or debri from around fuel pump.there is a locking ring that needs to turn counterclockwise.remove fuel pump and bracket assembly.discard seal.clean pump flange,surface and seal ring groove.apply a light coat of grease to seal to hold in place during install.put seal in ring groove.install fuel pump and bracket carfully to ensure filter dont get damaged.make sure the locating keys are in keyways and seal stays in groove.hold pump in place and install locking ring finger-tight.make sure locking tabs are under the tank lock ring tabs.rotate lock ring clockwise intill it stops fully.put tank back in car.make sure all connections and lines are tight.put only 10gals in tank and check for leaks.put a fuel pressure gauge on the valve on the fuel rail.turn ignition on,but dont start.turn ignition on for 3 seconds then back to off.repeat this 5-10 times or until pressure is at 35psi.if you dont get 35psi or it drops back down check for leaks.if it stays at 35psi then remove fuel pressure gauge and start car.while running check for leaks.this is directly from ford motor co.verbatom.good luck.

sound like to me that u are getting air from somewhere one of your lines may be cracked or not tighttend all of the way or you may have overtightghted one of them