[01cbr929]

B) You have a leak in the tank thats releasing pressure (Most likely)

I'm going with a split fuel line in the tank, between the pump and the hanger. It happened to me... it could maintain fuel pressure under light throttle, idle ok... yet couldnt deliver under boost. BTW many fuel pump kits have a standard hose clamp and not a fuel line clamp. A standard hose clamp cuts into a line when tightened hard... where a fuel line clamp is smooth. Pic below....

 

[01cbr929]

Interesting. Could you tell me more of your symptoms?

Well, it didn't go from being a-okay to lean... but more gradual(slowly splitting). No gauge in the car to see it fluctuate. Slowly over time(maybe a tank of gas or 2, not too long) it started getting leaner and leaner... progressively worse as time passed. It takes about 10 minutes to pull the hanger out. I would pull it, and examine the entire fuel line.. b/c it doesnt always make itself obvious. Bend it around, flex it... to make sure no slit reveals itself.

double check vacuum line to regulator?

Wouldnt hurt to check it(easy as poo)... doubt it's this, as it hits 70psi then falls though.