350 Mag fuel system questions
08-30-2010, 09:28 AM
#1
Registered
Thread Starter
350 Mag fuel system questions
Hi Everyone,
This is my first post on this forum and please excuse the length. I've recently purchased my first powerboat (2000 Scarab 29 with twin 350 Mag Mpi's) after spending many years with cruisers. I wanted fuel injected engines for their convenience and fuel economy.
I didn't realize when I purchased the Scarab that at some point a previous owner had modified the fuel system. I have been having trouble with the starbord engine not revving evenly with the port engine. I checked compression changed plugs, wires, distrib cap, rotor, ignition coil and now they run a bit more evenly until around 4000 rpm.
I then checked the fuel pressure per the Mercruiser manual. The port engine has 25psi of fuel pressure at 1800rpm and the starbord engine has 19psi of fuel pressure. Mercruiser says the spec is 30 psi at 1800 rpm. The cool fuel system has been removed on the boat and the fuel pumps are now mounted on the firewall of the boat below the fuel tank level. I suspected the the pumps were getting weak. Unfortunately when I ordered the cool fuel pump and cooler setup the new pump is shipped with no thread on the delivery side so I cannot attach it to the fittings that are now in my boat.
So over the weekend I decided to swap one of the pumps out for Sierra part # 18-7330 which is the high pressure pump from a Volvo penta 5.7 MPI and rated the same as the Mercruiser pump 50 gph at 45 psi and with the appropriate threaded ends. When I started the engine that pump is holding 50 psi at 1800 rpm which causes the engine to run far to rich. My assumption is that someone has removed the fuel pressure regulator when they installed this system and simply deadheaded the pumps.
What I'm planning to do is install an Aeromotive universal fuel pressure regulator and adjust it to the 30 psi that the engine requires. I'm planning install the regulator after the fuel pump on the firewall and before the fuel water seperator with a loop the returns the pressure to a t in the line behind the fuel pump. Will that work ok?
This is my first post on this forum and please excuse the length. I've recently purchased my first powerboat (2000 Scarab 29 with twin 350 Mag Mpi's) after spending many years with cruisers. I wanted fuel injected engines for their convenience and fuel economy.
I didn't realize when I purchased the Scarab that at some point a previous owner had modified the fuel system. I have been having trouble with the starbord engine not revving evenly with the port engine. I checked compression changed plugs, wires, distrib cap, rotor, ignition coil and now they run a bit more evenly until around 4000 rpm.
I then checked the fuel pressure per the Mercruiser manual. The port engine has 25psi of fuel pressure at 1800rpm and the starbord engine has 19psi of fuel pressure. Mercruiser says the spec is 30 psi at 1800 rpm. The cool fuel system has been removed on the boat and the fuel pumps are now mounted on the firewall of the boat below the fuel tank level. I suspected the the pumps were getting weak. Unfortunately when I ordered the cool fuel pump and cooler setup the new pump is shipped with no thread on the delivery side so I cannot attach it to the fittings that are now in my boat.
So over the weekend I decided to swap one of the pumps out for Sierra part # 18-7330 which is the high pressure pump from a Volvo penta 5.7 MPI and rated the same as the Mercruiser pump 50 gph at 45 psi and with the appropriate threaded ends. When I started the engine that pump is holding 50 psi at 1800 rpm which causes the engine to run far to rich. My assumption is that someone has removed the fuel pressure regulator when they installed this system and simply deadheaded the pumps.
What I'm planning to do is install an Aeromotive universal fuel pressure regulator and adjust it to the 30 psi that the engine requires. I'm planning install the regulator after the fuel pump on the firewall and before the fuel water seperator with a loop the returns the pressure to a t in the line behind the fuel pump. Will that work ok?
