Jamie- I have no experience with SeaMaxx PCM's but have 2003 Crusader 5.7L MPI's made by the same company. I don't know what the differences may be.
Are you saying the LP pumps do not work on EITHER engine. That seems odd .
If the ign. switch is turned to On/Run and he cannot hear or feel the LP fuel pumps activating for a few second to build fuel pressure , the very 1st thing I would do is carefully check the fuses for the pumps and relays.
On my engines, they are on the top/port/aft part of the engine (just under the big aluminum engine cover & next to the valve cover) in a waterproof holder w/ retained cap containing at least 3 yellow 20 Amp ("mini"-size??) spade fuses. I've replaced 2 or 3 so far and keep spares onboard of course.
I also had an "rpm stumbling " issue that manifest occasionally for a couple years that was finally pinpointed when the pump did not prime for start one day and a thorough on-engine wiring harness "Wiggle Test" was performed. With ign switch turned to On, when the connector to one of the small black plastic fuel pump relays on top/fwd/port was wiggled, the fuel pump suddenly activated and the engine could be started. It turned out to be a very slightly bent connector pin in the connector, which when straightened, has worked fine for the last 7 years. So wiggling would be my second check.
Note that neither of the pump or relay issues will show up in the MEFI diagnostic scan devices or laptop software which get most of their info from ECM and connected sensors.
If , however, he can feel the LP pump running but it is not outputting fuel, check remote and on-engine fuel filters (near & to the LP pump) , tank or filter shutoff valves, A/S valve on tank , vent for restrictions , or fuel line suction air leak.
My engines were ordered with the optional Returnless Fuel System but I expect your neighbor's is standard Return system returning excess fuel to the tank.
If your neighbor's Owner's manual does not help, you and he might check Crusader's Owner's and Parts manuals for the 2003 Captain's Choice(MPI models) 5.7L engines:
http://www.crusaderengines.com/Owners Info/manuals.html (They've already replaced the 2002 manuals there with 2010, and for some reason have not been adding anything newer yet.) The parts manual will show relays , pumps , fuse holder and connectors on the Crusader engines which likely share some parts at least.
The only thing I could find re:SeaMaxx engines was this older parts diagram & list , which does include the LP & FCC HP fuel cell on manual p, F2-2 to F2-4:
http://www.marinepartsexpress.com/PCM_Schematics/PCM_Marine_Engines_Complete_Large_File.pdf
FWIW-There is also a hardcopy MEFI 4 Diagnostic Manual available from Crusader distributors for ~~$100 ( or included "free" in the accompanying CD with Rinda's Marine Diacom diagnostic software for laptops.) I highly recommend anyone with a marine MPI engine with MEFI ignition to get themselves at least ready access to a MEFI scan device and diagnostic manual to use together.
