Running a Holley mechanical pump on a mild 440 in my friends Valiant. Fuel pressure has always been about 7 PSI. When the car is cold we only have about 4.5 psi and as it heats up it drops to 0. Someone suggested vapor lock, but how would that explain 4 psi cold??. Tank is new, lines are new. We tried a new pump and that didnt work. Sounds to me like someone dropped a rag in the tank. Any thoughts??

If you are using a liquid filled gage to check pressure, well then, there is your problem. The sealed gage heats up and gains pressure inside which counteracts the pressure recieved from the outside, giving incorrect reading. Now, if you are using some other gage, well, maybe you actually have a problem.

I had a similar issue with intermittant fuel pressure and no starts on my GTX (but don't have a FP gauge). Ended up being the actuator rod being worn down on the cam end. A trip to Mancini, a half hour and $12 bucks later... problem solved!

Good luck!

I am having the same problem. Experiencing fuel starvation. I have installed a Carter electric pump that I turn on when car starts to die.

On mechanical pump 7 psi at cold start up. Sitting at idle,in 15 min preasure will drop to
1-2 psi ( Liquid Filled gauge). Turn on elect. pump, preasure goes to 4 psi.

3/8 in. sending unit and fuel line. I have installed a 1/4 in. return line and filter going back to 1/4 in line on sending unit. This did not solve problem.
I am not using a return regulator at this time.

The next thing will be a 3/8in. return line going into the fuel filler pipe in the trunk.
and a return regulator.

Any sugestions would be appreciated.

If you think it's a blocked sending unit run a line into a can...Is the carb on the hot intake or does he have a spacer? ALWAYS get the carb off the intake. And how does a rag get into a gas tank?

The carb is on a cold manifold with a spacer. As far as the rag goes, the car is stored in a community garage and some people have been complaining about the noise.....so maybe some spite work!!

As said I would check your fuel pump pushrod if it has any kind of miles on it & there was a run of bad ones

Did you ever resolve this issue? I'm interested in your findings.