I thought that I read once that the banjo bolt (pressure relief) on the VP 44, if you tried to blow thru it, that it would be very hard to do, I pulled mine and I can blow thru it with very little effort, if this is the case what would the symptoms be? low power? or just low fuel pressure?

 

The check valve that returns fuel to the tank has both a bleed to allow air to pass and a spring-loaded overflow valve. The spring-loaded valve opens between 10 and 14 psi and allows greater flow back to the tank. When the engine is at low idle, the spring-loaded valve may never open. Blowing through the spillback valve is no way to test it. Also, it is a popular myth that the lift pump fuel pressure controls this valve.

 

a picture is worth a thousand words, thanks Dave. that will explain why it "blows" through so easy, the air is bypassing the check ball via the bleed orfice,
Would it be better to say that this valve controls the lift pump pressure? as if the spring was weak the fuel would return easily resulting in lower fuel pressure

 

Absolutely not. It is nothing more than a check valve that is designed to keep fuel from draining from the injection pump. The FSM is very specific about this point. The check valve does not have enough capacity to drain a lot of fuel into the return line, so a high performance pump will immediately overpressurize the VP44 if you do not install an extra overflow device. Also, the valve is not very accurate, its specs are: must open at 14 psi; must close at 10 psi. That's it.
-P