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One thing I found interesting is that if I pushed the PRV plunger or piston (not sure what it is called) back to simulate an overpressure condition in the fuel system it locks into an open position and does not reset itself.
Black306; Thank you for your in-depth explanation.
There is one thing I think you missed. On the PRV side opposite the brass check valve (on the other end of the spring) there is a part that resembles a barrel or a piston. That part is free to move left and right as orientated in the picture. If you look closely at the two side view pictures you can see that the barrel is in two positions. This is the part that I was referring to as “locking in the open position”. In the picture you used, it is in the left position.
I think the reason the PPRV is in these cars is quicker starts. They (Ford in this case) wanted to hold pressure in the fuel system after shut off for quicker/easier starts. So they had to put in a check valve to prevent the fuel pressure from bleeding off. That opened up the possibility of the fuel system building up too much pressure after shut off due to heat build up. So they had to put the PRV valve in it.
They then took it a step further, to prevent damage to the FRPS and keep the fuel pump hoses from popping off (some are heat shrunk on), and provided a feature to prevent overpressure while running. That is the barrel part I think and this is where we have the problem.
When we remove the PPRV we no longer have the worry of overpressure due to heat build up after shut off because we also remove the check valve that holds pressure after shut off. This results in a longer start (fuel pressure needs to build up) and the possibility of over pressuring the system while running and causing the FRPS or fuel pump hose to fail.