Quote Originally Posted by edmayo View Post
Just simply remove the feed line from the discharge of the pump which goes up thru the frame section right where it enters the inlet fitting of the fuel filter console. Install a pressure gauge there and see if you're getting 30 psi or so of pressure, then run that hose into a small coffee size can and the pump should fill that in less than a minute. If it does all that then jack up front of car and repeat. If it fails that then fill a five gallon can with gas and with several feet of extra fuel hose run the car at an angle from the five gallon can. This will prove whether it is a pump problem or a fuel feed problem involving the car's gas tank and lines. And by the way make sure that the fuel hose from the bottom of the filter is going to the passenger side of the MFI pump, and the driver side of the MFI pump is going to the inlet fitting of the console. ( the fitting facing rear of car)
Well, I'm back, and no less frustrated than before.

I started going through some of the tests here with a borrowed pressure gauge. Pressure at the inlet of the filter console would jump to ~40 PSI when the pump was switched on, then the pump's relief valve would open and it dropped to a steady 28 PSI and stayed there. Did not matter the attitude of the car, same result with the nose in the air.

Verified that the lines to and from the MFI pump are correct, bottom of filter to the right side of the pump via large banjo fitting.

Started to look into volume testing by running the pump into a bucket, but noticed that the fuel pump was starting to leak again. (I had replaced the large o-ring that seals the motor case to the pump body before I got into this process.)

As a stopgap to deal with the leak, I bought a 2-port pump conversion kit from Zims to get the leaking pump back off the car. (Will decide later if I want to try to rebuild my original or buy one of the new Chinese pumps from Porsche Classic.) This new pump eliminates the bypass valve and return hose from the pump, and uses the check valve in the filter console to regulate pressure. (My check valve is new and factory Porsche part.) So I can no longer check pressure at the inlet side of the filter console. I will need to check it between the bottom of the filter and the MFI pump inlet. But I had to return the borrowed gauge, so I have not tested pressure since the pump replacement.

But I'm going to guess that with this new pump in place I shouldn't have a shortage of pressure. And...

No change. I'm not really certain at this point if I am really losing pressure when I start up a grade, or if it is just that going uphill just puts more load on and it starves out. But the result is that trying to pull up a modest grade at normal RPMs for town driving runs it out of fuel. Sputters, pops, and will even sometimes die.

I feel I must be missing something very basic. I will get the gauge back tomorrow for a bit more testing with this new pump. I will (assuming the pressure tests out OK) go back to the volume test into a can, and probably also try to run the engine out of a gas can to eliminate all existing tank and line possibilities.

But I'm really starting to wonder if there is something else afoot. Could the MFI pump itself have issues that would manifest themselves in this way?