Mag MPI 350 Fuel Pressure Problem

[redboat01]

Engine: Mercruiser MIE 350 MAG MPI Ski
Serial: L674911
Year: 2001
Ski Supreme

I took my boat in this spring for a low RPM shake/vibration issue. After fixing the shake, the mechanic calls me back and says that I have a low fuel pressure problem and it would cost $850 to replace the fuel pump and fix it. Well I wasn't ready for that bill so I decided to pick it and check it out myself. I ended checking the fuel pressure with a tire air gage and got a reading of around 20+psi.

I ended up replacing the fuel pump for $150 ((861156A1) but the pressure was still showing around 20psi. So I rented a fuel gage from napa and got a reading of 25psi.

I then decided to replace the fuel regulator (807952A1 with pink stripe) for $90. The pressure still reads 25psi (tested out of water at idle and revved).

I've read through some of the other posts with similar subjects and was wondering what I should do next.

Thanks, john.

 

[Don S]

Re: Mag MPI 350 Fuel Pressure Problem

Head up to the Adults Only sticky at the top of theis forum and download the OEM service manual for your engine. #24 is the one you want. Then follow the troubleshooting chart to find out exactly what the problem is. You are just throwing parts (aka money) at it with hopes of curing the problem. As you can see, it's not working.

 

[redboat01]

Re: Mag MPI 350 Fuel Pressure Problem

From what I can tell in the service manuel, the operating pressure is suppose to be 30psi. The only symtoms I have is a fuel gage that reads 25psi and a mechanic that said it should be 40psi.

Do you think I have a problem?

 

[redboat01]

Re: Mag MPI 350 Fuel Pressure Problem

More Questions: For the experts. JoeBoater is seriously confused.

Manuel 24 states a fuel pressure of 30psi on 5C-2, but on page 5G-32 it states 34-38psi. What is correct?

If I get a pressure of 25psi after the engine is started, is this close enough?

Can you rent a Scan Tool or Code Mate Tester to perform the OBD System Check page 5G-25?

Following the steps on Chart A-4 page 5G-33.
1. Skipped OBD test
2. Fuel pump ran, but system pressure was 0psi. (Fuel pressure raises slowly to 25psi after starting engine.)
5. No pressure
Go to chart A-5 and start by testing fuel pump relay.
I have not performed this test yet.
Does this sound right at all?

Or should I perform the tests "How to: Testing your boats fuel system"
for airbound leaky system or vaccum leaks?

 

[redboat01]

Fuel Presure Test

Fuel Presure Test

Step 1 of the airbound leaky system test says to "splice the clear test line..." Where should this line be spliced?

Thanks for the clarification.

PS. Can anyone help out on the last post?