The actual regulator (one that set’s the psi) is #15 in this microfiche pic:
Also see:
https://www.mercruiserparts.com/bam/...31341/7595/120


https://cimg5.ibsrv.net/gimg/www.off...ce88b5f96e.gif

right, I replaced that regulator as well as the elec fuel pump in the cool fuel system. How could the metal filter that as the back of fuel rail get plugged or fail?

How does a filter back there get plugged ? Debris after the fuel water seperator filter. From degrading fuel / fuel line / fuel pump/ fuel pump modules : etc.

You should see all the crap i find in filters after the sepetator filter. These pics from various fuel systems (4 different boats) just this year ;


https://cimg7.ibsrv.net/gimg/www.off...878d7fbc8.jpeg
https://cimg8.ibsrv.net/gimg/www.off...0ab1e5db6.jpeg
https://cimg9.ibsrv.net/gimg/www.off...013198433.jpeg
https://cimg2.ibsrv.net/gimg/www.off...bf68bb148.jpeg
https://cimg5.ibsrv.net/gimg/www.off...e4ecdbe39.jpeg
https://cimg6.ibsrv.net/gimg/www.off...711d6e777.jpeg
https://cimg7.ibsrv.net/gimg/www.off...d85af45a9.jpeg
https://cimg8.ibsrv.net/gimg/www.off...604212790.jpeg
https://cimg9.ibsrv.net/gimg/www.off...d1a5d8851.jpeg
https://cimg0.ibsrv.net/gimg/www.off...dc38d4a46.jpeg
https://cimg1.ibsrv.net/gimg/www.off...c3ebff15c.jpeg
https://cimg5.ibsrv.net/gimg/www.off...a21ede1f6.jpeg

Well I swapped the rear metal filters and no change either. I will get a mechanical fuel psi tester this afternoon to verify my psi. When running on the hose at idle now I’m only seeing about 12-15 lbs on my gauge, doesn’t not increase with rpm. If my mechanical lift pump is bad, could that cause this issue or would I net see fuel at all to the electric pump if the lift one is bad?

again, appreciate all the help guys

Ok, so I just cracked the fill plug for water/fuel pump and it is over full of fuel/oil mix. Definitely a lot of gas in there. Lift pump must be leaking and not putting enough pressure to elec pump?

That is fairly common issue with those. Time to replace, I do not think they are rebuild-able.

I have early HP 500EFI's, they do not have the mechanical pump just the electric. They can sometimes get vapor lock and loose prime. I need to add the electric low pressure pumps to mine.