Loss of Power - 350 MAG MPI

[boatwakes]

There's only a high pressure pump on that engine. The way to test it involves the Schraeder valve (bike tire valve) at the front of the fuel rails. It's on the starboard side of the engine so for your application, look engine front on the port side of the boat. There's a protective cap on the valve and it unscrews. Get a pressure gauge from the auto parts store that reads to at least 50psi. Your fuel pressure at any rpm should be 30psi +- 2psi. There's a vacuum line that runs from the throttle body to the fuel pump, make sure that's connected too. The fuel pump on that engine is going to suck to change, it's on the engine port (stbd side of the boat) motor mount in a pretty plastic box that says Mercruiser cool fuel.

[rphipps]

I tested the pressure at the rail and it was holding right around 24/25 psi at idle and dropped to right around 20psi as I increased to about 2000 RPMs. Just re-reading your note however, I didn't check that vacuum line. Will have to take another look at that in the morning. I really don't know much about this stuff, but if the fuel pump is bad, would I even be getting readings in the 20+ psi range? And I see what you're saying about the location of the fuel pump; that looks like a bear to get in there and try & swap out.

[Thegerman618]

Yes, with a bad pump it will still show some pressure but when the load is applied it fails to keep pressure as your seeing now with drop of 5 PSI but your idle pressures are already to low like Cory (BoatWakes) said it needs to be at 30 PSI +/- 2 PSI constantly. The pressure drops will be worse and faster when you have a loaded boat.

[Thegerman618]

It will be a completely different boat after you get that thing fixed, slug bug to Ferrari.

[MOTige]

I have a 01 22i with the same motor/same issue. I have changed the fuel pump but have not had it on the water yet.
Pressure would read 28psi(who knows if the gauge is calibrated) and then bleed off to below 20psi with key on not running before I changed fuel pump.
New pump holds 28psi when not running but drops off 1-2psi when running(on hose) and really drops off when you chop throttle.
I would have thought there would be a pump at the tank to lift fuel to water separator, but I have 0 pressure on that line.
Any input?

[rphipps]

Any tricks you can offer to getting the plastic lid off the cool fuel box? I've got the replacement fuel pump but am having a heckuva time getting inside the box.

[boatwakes]

Bottom lip of the plastic box has a tab about an inch wide. Pull it towards the outside of the boat and lift at the same time. Another couch engineered piece of mercruiser crap. Be aware the fuel pressure regulator and fitting at the top of the old pump MUST BE REMOVED AS A UNIT if you're not replacing them (remove the two 5/16" head bolts) and the screen underneath as well. Don't try to remove the fuel fitting from the regulator if you're replacing the regulator, just buy another fitting because it wil break. There's also a crush washer behind the fuel fitting in the regulator so order new there too. Grease all the orings on the fuel fittings and use the high temp white paste for the pump housing to mount connection (you'll see the old stuff when you remove the pump), the two are not interchangeable.

In response to MO, when you chop the throttle does the fuel pressure stay low or come back? If it stays low, ch ck the vacuum hose to throttle body. If it comes back, that's normal. However, when do you ever chop the throttle when in gear?

[KXCORKY]

We are having the same issues, but now the boat wont start at all, will start when putting starting fluid in the carb then dies. We tried everything to get the black plastic piece off to access the pump, but it seems we have to take the whole motor off the mounts to get to it. Does that sound right or are we just not trying hard enough? Didn't want to break the box.

[boatwakes]

The pumps are held in place with nuts on studs on the motor mount, just remove the nuts, fuel line to the fuel rail and from the fuel filter, vacuum line and power quick connect. Theres also a high pressure fitting on the pump held in place by a captured screw, 5/16" head. Loosen the screw, but it will not be removable, it will just pull out of the way allowing the fuel line to be removed. Pull the water lines off both sides and replace the unit and all o-rings.