[Tommy]

Three thoughts on this, Ed. First, according to their web site info, the fuel pressure output on this pump is adjustable with an external pressure relief valve. Perhaps the original installer set it at 4.5 PSI. Second, if the pump was higher than the fuel level in the tank, and the pump had an air bubble in it, that may also have contributed to the problem. Third, if the owner does not have an external fuel pressure regulator, suggest he install one and reset the fuel pump to the full 14 PSI output. Letting the fuel pump regulate the pressure results in excess fuel being shunted from the output side of the pump back to the input side. On a hot day with a hot pump, this can overheat the recirculating fuel and create a vapor lock problem.

P.S. I suspect the problem was that your pump produced 4.5 PSI pressure on air before fuel arrived at it causing the internal pressure regulator to function. From that point on, the pump was simply recycling the same air. Opening the fitting at the filter allowed the pressure on the output side of the pump to drop below 4.5 PSI, bypassing the internal regulator and allowing the pump to push the air out and get to the fuel.