502 MPI Fuel Pump Problems
 

I am working on 502 MPI MEFI 3 motor with a fuel pump problem. This boat has triple 502 MPI, the other 2 pumps prime and sound about the same, whereas the port pump sounds weak and different. I assume it's a bad pump, but I'd like to check the pressure before I may need to pull the motor to access the pump.

Is there a schrader valve to check fuel pressure on these?

I have searched the diagrams and have not been able to locate it.

Thanks.

Okay I removed the fuel pump, but what's interesting is how does the fuel pump connect to the high pressure side? it doesn't seem like it has any fitting and just Falls right off I checked in all three are the same.

Also, the furl pressupr regulator vaccumv line juat falls right off as well, its I'd do that it doesn't have any hose clamp

Since your saying MEFI 3 you will have Gen 2 Merc cool fuel for the stock OEM engine if this is the case I would invest in the proper service manuals if you are working on your app. IMO that is the first step to help one with the many questions they might have looking for answers and procedures before they even start pulling wrenches out. Solid advice for all boat owners.

Next would be quality testing tools in hand - fuel pressure gauge. scan tool, noid lites, inline sealed spark testers and so on for when they are needed

Thanks for all your help.

Got it all fixed, replacing the fuel pump fixed the problem.

The fuel pump is pressed on with 2 o-rings to sea on the elbowl, the bracket holds it together somewhat.

Middle engine had a problem with the fuel pump relay, it was able to pull 12v on the test light, but would not turn the pump. Hammering on the relay got it primed and working, ordering a new relay and a spare.

The fuel pressure regulator vacuum hose can be held on with zip ties, however the hose must be very clean since there is no barb. Replacing the host is an option as newer hose is unstretched, and will likely fit tightly.