Need Advise.. 3.6 fuel pressure problem, need a BTDT, fuel pressure unreliable(long post) Options

[RON S.]

Guys,


A couple of years ago while the car was just idling in the yard I noticed the RPM’s beginning to fluctuate. Upon further inspection I noticed that the fuel pressure was swinging wildly along with the RPMs until the FP dropped below 30psi, and the car stalled. The car would crank right back up but w/in 2 minutes the fuel pressure would begin to do the same thing.
At this time I had an MSD electric fuel pump under the tank pushing fuel to a Bosch Mustang GT pump mounted in the frame rail closer to the engine. All was plumbed with -6 hose, and a 3/8’’ steel return line through the tunnel back to the tank. Both pump were relayed. With an electrical meter I noticed that there was a voltage drop both up & down as the pumps would begin to cycle erratically. This led me to change the 993 main engine wiring harness because it was bad anyway. The problem was still there. I realized that the relays were wired incorrectly as the wires were getting hot so I corrected that but still have the problem. I thought that 1 pump was overwhelming the other so I removed the Bosch pump and ran solely on the MSD. The wires were then cool to the touch and there was now a full 12 volts to the pump at all times but the unit would still begin to cycle after a couple of minutes.
I now decided to step up to a better pump, and bought a Aeromotive pump and 100 micron filter. Upon removing the previous pump and filter I noticed that the filter was clogged with trash from the tank that it picked up. Well I thought, problem solved with the new unit.
I installed the new pump running -8 supply line to the pump. I Tig’d a -8 fitting on the 914 supply flange nut, and screwed it back under the tank. By the way, the supply hole opening on the 914 tank is the same ID as the -8 fitting. No restriction there. Cranked it up, ran fine, but overly high fuel pressure. 60psi plus.
With all this installed, the car has run reliably for a year. This year we overhauled the engine. I finished the engine, reinstalled, and everything worked perfectly for about 150 miles.
I added the fuel pump controller thinking it would bring the Fpressure down some but it doesn’t so, I decided to add the regulator to bring the pressure down. After installing it is when the wild cycling began again.
My first thought was fuel starvation due to another clogged filter. The Aeromotive unit is cleanable and sure enough it was packed pretty good with trash. replacing it did not solve the problem. The fuel supply line is completely free and quickly empties the tank when pulled.
The fuel line is only about 2’ long, and the pump is mounted lower than the tank for a good gravity feed. The car currently starts every time but within a couple of minutes, it begins to experience fuel starvation.
I removed the pump per the pic, and laid it in a pan of gas with the regulator installed. I ran the pump off a battery charger for 30 minutes @ an adjusted 55psi, and it ran flawlessly. The needle on the regulator never moved. I did put a inferred temp gauge on the pump and it indicated 109 degrees after 30 minutes of use which I thought may be high, but it ran fine.
I reinstalled the unit back in the chassis, and the problem was still there.
The pump sound like it is cavitating or maybe vapor locking.
Give me some ideas, what am I missing?? A fuel delivery system is not rocket science. The car will not run dependably until this is fixed.
the pics show how all is set up now. This weekend i'm going to run the supply line into a gas can to see if that will run ok. if it does i'll suspect the tank, and if it doesn't I'll suspect the pump.

Any advise is appreciated.

Ron