Leaking gas on top of left cylindar head

Probably either a leak in the gas lines or connectors at the top of the tank, or gas leaking past the pump/sending unit gasket there.

Does the pump have wick disconnects that required a tool to remove them? There are orings in those as well as a large oring sealing the pump to the tank. Make sure the connectors click when you replace them. The pump should activate with the key on. " not started", you should be able to see if the lines are leaking or if it just your fuel fill overflow hose leading to the fill door alongside the large full hose.

the top of your fuel tank is where the fuel pump and such is installed.there sealing gaskets fail and can be hard to get sealed sometime after puel pump replacement

There are two hoses running from the filler neck. Either of them could be leaking from the top. There is also a seal on the top of the tank where the fuel pump is that can leak. If your car leaks the whole time you are putting fuel in, I would suspect the hoses. If it only leaks when you get it full, then check the seal on the top of the tank. The top of the tank can be seen without dropping the tank. Remove your back seat and you will see a cover over the fuel pump. Remove that cover and you can see the top of the tank.

First check for leaks: the tank drain valve may not be closed or has something in it causing it to stick open. Check the line from the pump to the tank and the line from the tank check valve to the pressure switch if it has one.
If there are no leaks you have either a damaged piston/cylinder assembly, usually the seal ring on top of the piston or bent or broken reed valves. You just have to remove the head and valve plate to check the condition of the cylinder and valve plate.

A 99 is most likely fuel injected, so the fuel pump is inside the gas tank. The gasket for this is a large O-ring in the top center of the tank and is unlikely to leak. Thus your leak is most likely in the line, put it up on a lift at a muffler or oil change place and look underneath for the wet spot which stinks of gas, that will lead you to the leaking spot. Gas tanks themselves can leak due to corrosion, this can be where road debris collects on top, and if you have a skid plate under the tank corrosion can build up between the plate and the tank eventually eating a hole in the tank.

Good Luck

the pressure in the tanks is not enough to "lift" the fuel up to where the seal is on the top. the tanks usually have the fuel pump and level sensor mounted in thru the top. actually if there was a leak anywhere above the fuel level in the tank it would not leak fuel but leak pressure which you would not see. it most likely is a rust thru spot on the tank, it only needs to be a small pin hole for it to leak and it can be very hard to see.

If you have oil-less type of compressor you may be leaking pressure past cylinder/piston ring or just air leak. Easy to check. Spray soapy water on all connections, first with pressure in tank and motor shut off, then once again with motor running/pumping. Repair as needed. If no leaks remove cover to motor and move piston to top of cylinder and examine condition. If you see scratches neer top of cylinder, then pressure is leaking past vinyl ring. If cylinder looks shiny and smooth and piston vinyl seal looks intact, suspect problem with reed valves or head gaskets. Parts are avilable at sears parts on the web. Good holidays expensive.

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.

you'r EVAP system is not purging the system . I suspect it is your charcoal canister located in the left side of the engine compartment located near the master cylinder its a piece of cake to change it just slides up after you diconect the lines .