mcguffey4

i have changed the gas cap. i even took all the gas out of the tank. it still does it only when under a half a tank of gas . when i emptyed the gas tank th e fuel gauge showed empty. i don't know what else to check any suggestions

Highmiler

I still think that it is an issue with the pump or inlet line. A little leak in the inlet line (in the tank) will cause it to suck air when uncovered, or an intermittant/weak pump will cause the same problems; it doesn't have to work as hard if the tank is full. 90 Mustang has electric pump in tank, and fuel injection (that is sensitive to pressure drops). For Mustang, pump is under $100 (be thankful that you don't have a Honda or something), and I'd try to run the tank pretty low before replacing the pump. If you try to test, it won't run unless the computer sees the engine running (safety).
Small chance it is the pressure regulator (at the intake), but I'm not sure how it could be.
Let us know..

4eyedfreak

This is a long shot but was the car stored for any period of time? I ask because mine was stored for 11 years or so before i bought it. The guy bought it back in 83 and so fourth...but he drove it a little bit and then when he stored it he only stored with half a tank. I bought the car did some bun outs and then i had the same problem. The problem was when it was stored for so long the top of the tank rusted on the inside. My burnouts nocked the rust into the rest of the fuel on the bottom. I tried everything and then i realized it after my charcole filter (carborated car) had rust color to it. And not to mention my sending unit was a piece of rust. I replaced EVERYTHING fuel related and now its good as new. (it is new), Maybe check it out.

kartracer55

Ok, not correct me if Im wrong, but I always understood Vapor lock as being when the gas "boils" in the line turning into a vapor so the engine cuts off. Its a dead givaway when this happens because the engine will simply die when the engine reaches a certain temp in hotter weather.

No? Whats happening doesnt sound like "vapor lock" but either way its a problem.

HighMiler brings up a good point, and I think he might be on to something. Now, let me ask you this. If it cuts out, then you fill the tank and restart it, does it take a while to start or run rough for a little while? If so it would point to this being the problem, as the fuel pump will have pumped air and youll have air bubbles in the line for a while. Either way, it could be a problem with the pump/pickup... Id be more inclined to investigate this rather than the gas cap.

How can it be the gas cap? It doesnt make sense... This cap problem would be the case if you were using the first 1/2 tank of fuel, but If its always happening at 1/2 full no matter what level you started at, it probably wont have anything to do with tank ventilation... How would the ammount of vacuum in the tank possibly be the same if one day you used 1/4 tank and another day you used 1/8 tank to bring you down to 1/2 tank both times... see what Im saying?

Im no mechanic, but this is just my .02

Jim

mcguffey4

i found out the problem when i went to change the fuel pump the hose connected to the fuel pump had holes in ti so when it got below that point of the holes it would suck in air. thanks everyone for your help

Tims 88GT

kool glad u fixed it. But some one tell me how a Fi engine vapor locks?

ttoppedaerocoupe

vapor lock is when vaporized fuel is present in the fuel lines, not allowing the eingine to get the fuel required to run. When you draw a vaccuum on the tank, you will hear the hissing when you open the cap.

Tims 88GT

ok so they only way a fi car can vapor lock is if the pump dies?