Hello gentlemen

Here is the situation: fuel pump on 56 TBird (about 25K miles since new) was working fine but leaking oil through weep hole. Ethanol, thinks I. Figured I’d replace it. Also replaced the short flex line on the input side. New fuel pump (Carter 73063) worked fine for about 10 mi. Then fuel pressure fell to zero on pressure gauge on fuel rail. Engine would idle but would not carry any kind of load. Figured pump was faulty, replaced it with another. Experienced identical results—started up fine, showed steady 5 lb pressure, drove perfectly for about 10 mi, then began to run rough and ultimately died on side of road, presumably of fuel starvation. Pressure gauge at zero again. Barely idled. Limped home.

Retreived original fuel pump from trash bin and saw it was an Airtex 4406. Compared Carter and Airtex side by side, noticed Airtex had a slightly shorter pump arm travel. Significant? Maybe. Bought a new Airtex 4406 and installed it. Also replaced new flex line (tiny i.d. about 1/8” on brass fittings) with flex line with larger diameter fittings. Excellent steady fuel pressure initially, but after 7-8 miles of driving (engine up to temp) fuel presssure at idle drops to zero but recovers to 3 lb or so upon rpm increase. So i disconnected line to fuel tank and drew gas from a jerry can—gauge still read zero, although i only ran it that way about 30 sec. I blew compressed air backward into hard fuel line and heard gas in tank bubbling immediately. Tried replacing gas cap with a new one, then put the old one back then tried no cap at all. No difference. Fuel line filter element was clean, replaced it anyway.

My understanding is that fuel line assy from tank was replaced about 25000 miles ago. Car is always garaged, never sees weather, so I doubt the hard fuel line is rusted. I haven’t had it up on a lift yet, but am assuming there must be a rubber section of fuel line somewhere after the tank. Could that be the trouble? Tank is original to the best of my knowledge.

But its odd to me that there was never a problem until old pump was pulled off.

I will replace the line from the tank forward if i have to....Never done one on a bird but I’ve done shorter lines and brake lines.

Anyway, any suggestions or advice? Thank you.