I still need help. I've done another test on my 502EFI engines. Starboard engine won't idle well out of gear and will not idle at all in gear. We tested fuel pressure on both engines at schrader valve under plenum. Turn key on and both get 30lbs. Start port engine and pressure drops to about 28.5. Start Starboard engine and pressure drops way down to almost 0.

Ideas anyone please?

What year MPI motors? Cool Fuel or VST systems? Pressure difference between the two. It would appear that you are low for either system however and that will make engine do as you describe.

I just got done adding new regulators to my 502mpi cool fuel systems. Completely fixed my hard start and erratic/surging idle issue.

They are EFI, are VST and have additional mechanical belt driven fuel pump. Not sure exactly what year. When I purchased in 2002 they had just been completely rebuilt with roller rockers, bigger cam, springs, valves, etc. Motors have been extremely good for a long time but of late gremlins have creeped in. They were overhauled again about 5 years ago by a real dumb-ass. Last year was a fuel pump diaphragm ruptured in same motor as now and blowing fuel via overflow tube into intake. The guys that work on my motors are at the marina and are very good but they have little to no experience in trouble shooting these particular motors. That is, outside of my motors. This forum steered me to the ruptured diaphragm last year. My motors fire virtually instantly even after layup and I have no problem at all starting now either. I greatly appreciate your input.