I have 502's w/mechanical pumps.
Starboard motor runs fine all day, but time to head back to the marina won't start. Happened last 3 times out.

Fuel pressure on starboard motor close to 5 and fluctuates between 0-5. Port motor press. 7 (constant). Replaced pumps 2yrs ago.
Decided to swap pumps and see what happens.

I show same pressures on starboard and port motor. I pretty much can say that it isn't the pumps.

What about the cam/shaft in the seawater pump. Does this sound like symptoms of worn cam? I had noticed when replaced the impellors couple months ago the cam seams loose and free spins on the shaft.

This assembly is expensive and don't want to replace it if it is not the problem.

Any ideas/experiences.

It could be a worn sea water pump cam. However, When I rebuilt mine, I found there is a cup that is on the cam. The cup spins freely on the cam, so what you are describing isn't a symptom of a worn cam. I would check the stroke of the cam - measure from the fuel pump mounting surface to the cam with the cam at it's lowest point (relative to the mounting surface). Rotate 180*, then measure again. Compare both pumps to see if that is the difference engine to engine.

Found out if the pumps have leaked fuel into the cam housing, this will wear the cam out, bearings, seals, etc.

I did have fuel in the housing couple yrs ago and I did replace the pumps. I think it has finally caught up to me and wore out.

I am going to be replacing the housing.