Fuel pressure at WOT

Got a fuel pressure enigma that is baffling 1972 Monte Carlo with a 402 the car has run flawlessly for 3 years on a rebuild ( 9to1, small cam, fact intake and exhaust manifolds) at about 3500 rpm, the car falls on it's face and pops out the carb...classic fuel starvation. Changed the fuel pump( stock) and problem still persists. Hooked up fuel press gauge- 4.5 psi at idle and at 3500-4000 rpm under load, press goes to zero and pops out the carb. Changed the pickup and sock in tank, all new now. Problem is still present. Inspected the factory 3/8 steel fuel line- all good. Blew fuel and vent lines with compressed air, no blockage noted. Checked the fuel filter in carb (one of the first things checked) no dirt, changed it anyways.
Carb is factory Rochester rebuilt by jet performance in cal. Idles and accelerates perfectly.
This car ran perfectly and pulled hard to 5500rpm for three years, ran low 14's consistently.
Any ideas would be appreciated

look for cracks in the rubber hose on the tank end ,, and you may try a pass without the gas cap on .. iv`e had a vented cap stop up and cause such grief ..

Thanks for the reply I'll try a different cap

40 year old rubber hoses---new modern fuel that ain't compaable

Quote:

---

Originally Posted by jerry clayton

40 year old rubber hoses---new modern fuel that ain't compaable

---

Amen, Jerry. My son's Mustang sat almost two years and the rubber hoses on the fuel pump turned to a slimy reinforcment tube, and every injector was plugged with that junk.

Actually, the hoses were replaced a few years ago. I'm going to take the cap off and run it to see if the charcoal canister or venting is the issue. It's the only thing left to try as I have tried everything else.
The only other thing is to try out a a higher psi mechanical pump. The stock pump has worked for years. I don't know why it all of a sudden would not work adequately. Thanks

It could be something as simple as the stock fuel pump in the failure mode.

We just went through a few evenings of chasing a fuel problem on my kid's rpu. First in line after tank is a fuel filter, then a Carter electric pump, then a Mallory fuel pressure regulator with hose going to a fuel log on the firewall. If we let the car sit for a day the fuel pressure gauge would read zero and when you pulled the line off of the carbs it was bone dry.

The electric pump was working fine and when we pulled the line off the end of the regulator it was dry, so we felt it was sticking. Tore it apart, nothing wrong. Finally, we removed one AN fitting going into the fuel log and there was some kind of gooey stuff in it, sort of like clear silicone. We cleaned that out and the problem went away. We have no idea how clear silicone got into the system since he used none anywhere, but we suspect the one fitting he pirated off of the Camaro drag car engine I have might have had some inside where we missed it when we cleaned it up to use.

The silicone was evidently acting as a flap and would sometimes let fuel pass and then close up and not let it pass. Very strange.:confused:

Don

First I would agree with the other guys check all your lines real good.
I am not sure how your tank is set up, Have you cleaned it out lately.
It could be suckin trash off the bottom of the tank and makin it starve for fuel.
Are you using Mech or Electric fuel pump? Next there is a lot of water in the Ethanol
that they are putting in the gas now, you may want to make sure the fuel bowl is not half full of water. I just had to order a new carb for my wifes vette because of the Ethanol had that had white stuff like you get around your old fawsets.
It was all thru my carb,with alot of the white crusty stuff in the fuel bowl.
The Ethanol will also eat up rubber hoses and put all kinds of debre in the fuel line and carb.