Air in fuel line before pump?

I just replaced the pump on my truck because it kept cutting out but after sitting fo rafew minutes it would run fine agian the cut out. so i was going for a test drive to make sure everything was ok and it did it again,and again. so i look under the hood and the fuel filter it full,then i loosened the clamp on the inlet side of the pump and could hear air whistling and it was bone dry,stuck it back on and ran fine for a mile then did it again. anybody have any idea on whats going on?

 

Probably vaporlocking in the pump. Had a 69 camaro that did that until i plumbed in a return line and put on a pump with return line.

 

But you might make sure the tank has a vented cap on it. The whistling you hear might be the tank ****ing air back in when you crack the fitting.

 

Ok i thought vaporlock was a heat problem. so basically i have air building up in the pump until it no longer lets fuel in?

 

try driving it with the fuel cap off. if it runs ok, the vent is plugged.most "old" cars had vented fuel caps and they are hard to find these days because of emissions. they dont want the nasty fumes venting to the atmosphere.

 

the cap vent is clear since i can blow air throught it. Just a dumb idee could i put a t at the output and run a small line back to the tank to bleed of air or would all my fuel want to follow that line

 

are you sure your pump is putting out the psi you need?

 

good question,how can i tell?

 

is it an electric pump off of the tank or the mechanical one at the engine?

 

Fuel pressure gauge. Also, I've seen systems draw air in from the suction side w/o a corresponding fuel leak.

 

uuhhh, just because you can blow air thru the cap does not mean that its vented...lots of caps are "pressure relief" but not vented...as i sugested before, try driving without the cap and see what it does....
dave

 

Some of the older gas tanks have the fitting at the bottom. If there's any "gunk" in your tank it can slosh around and cover that fitting - all or partially. I had that problem on my '47. It'd drive fine for a little while then **** out. I'd crank it for a few seconds and it'd fire right back up - idle forever. In my case there was some **** flaking off the inside of the tank - it'd slosh around and SOMETIMES cover the fitting. It'd restrict the flow so that while driving it'd die, but it would allow enough to flow that when idling - it'd idle all day long. Just a thought.

 

Check the condition of your rubber hoses between the fuel pump and gas tank. I had a doozy of a pain in the *** to diagnose, that the hose between the tank and frame rail was old, and porous. Wouldn't leak, but would **** air in under vacuum, and the car would cut out, run out of gas, even with a full tank!