Low fuel pressure, fuel filter half full while idling.

[ZafSC]

I recently got this boat. Mercruiser 5.0 MPI, Alpha1 Gen2. Had the engine checked at a mechanic running on muffs, and he showed me the fuel pump half full, and he said engine wasn't working at full efficiency. He said either air is coming into system, or fuel is leaking. Then I took it on the water, and he was right, it stalled sometimes during idle, or while putting into gear. When stalled, it restarted no problem, every time. I didn't notice a fuel leak in the bilge area, but it does smell heavy in the engine compartment. So I drive while engine area open. New spark plugs, new fuel filter.
Today I ran with the muffs, measured the fuel pressure. It changes between 32-34 psi. Increasing throttle doesn't change the fuel pressure.
What do I do next? Change the distributor rotor maybe?
Thanks

 

[alldodge]

Might be the regulator or the pump
Could remove the return line coming from the Reg at the fuel filter head. Plug the filter head and hose end, then just key ON a couple times (do not start) to see if pressure builds above 40 psi. It should go close to 60

If it does increase, remove Regulator and bench test it with air and a small adjustable air regulator

If it doesn't its probably the pump or has an air leak

 

[dubs283]

OP already has a thread regarding this (among other) issue(s)?

Regardless, agree with dodge and would add a vacuum test on the fuel supply could reveal a restriction prior to the fuel pump

 

[ZafSC]

OP already has a thread regarding this (among other) issue(s)?

Regardless, agree with dodge and would add a vacuum test on the fuel supply could reveal a restriction prior to the fuel pump

I guess I need a lot of learning to do :-(
I believe the idea is to stop the pressure getting distributed by blocking the fuel return line. Attached is the fuel regulator (I guess) and fuel filter pictures. Which hose do I need to remove? How will it stop the pressure leak by removing any of the hoses?
Thanks

 

[Scott Danforth]

if you smell fuel, you have an issue

you remove the vacuum line on the regulator to test. without the vac reference signal, the regulator should close

title of the thread says the fuel filter is only half full. how can you see how full it is? its a metal spin-on filter.

 

[dubs283]

Which hose do I need to remove? How will it stop the pressure leak by removing any of the hoses?

First picture shows the fuel out and return lines at the water separator housing. Second picture shows a fuel regulator on the fuel rail which in most cases isn't the regulator in question. Mercruiser used a few different styles of fuel supply systems over the years and in many cases added the pictured regulator as a damper for injector pulse control

The regulator in question is most likely located in the cool fuel module located low on the engine between the block and motor mount. To test the regulator you simply connect a fuel pressure gauge at the fuel rail, start the engine and with the engine running observe the fuel pressure reading. It should be withing spec, if not you remove the vacuum line at the pictured regulator/damper and observe the fuel pressure guage. If the pressure increases, the regulator is operational and the issue lies elsewhere. If there is no change in fuel pressure or there is fuel present in the vacuum line the issue is with the regulator and possibly other components

 

[alldodge]

I guess I need a lot of learning to do :-(
I believe the idea is to stop the pressure getting distributed by blocking the fuel return line. Attached is the fuel regulator (I guess) and fuel filter pictures. Which hose do I need to remove? How will it stop the pressure leak by removing any of the hoses?
Thanks

The Reg that goes back to the filter is under the port side motor mount. There is a black plastic cover over the pump and Reg, Need to remove the cover so you can trace the line back to the filter

The filter should have 3 lines on it. Rubber from the tank
On top of the filter head there are arrows above the braided lines. One going OUT will go to the pump. Arrow pointing IN will come from the Reg

 

[ZafSC]

Sorry, I can't find anything that resembles the fuel pump, fuel cooler or fuel regulator. The Mercruiser service manual (#24) shows differents pictures that I see on the engine.
Attached is the pictures taken from starboard side (snap 2,3,4) and front (snap 1), can you point out the above potential hardware?
Thanks

 

[alldodge]

The first pic shows the 2 lines going in/out
This pic shows the box it's in

 

[ZafSC]

After removing the two batteries, I clearly located the cool fuel unit with naked eye, but there is no space to work in the circled area (port side). I can barely reach it, let alone to work on it, by leaning on the engine (with a blanket between my chest and the engine).
How do you guys work on those? Lift the engine with a crane??

 

[alldodge]

Either need to find a skinny person or stuff has to be removed. It's a B***h but it's also a boat.

Suggest start by removing the exhaust manifold.
After removing clamps and pipes, remove the outer most bolts holding the manifold. Take bolt to hardware store and get about 18 inches of all thread rod same as bolt

Cut all thread in half and screw into the outer bolt holes. Now remove other bolts and its ready to remove. The all thread allows all the weight to be held until its ready to slide off and up

 

[dubs283]

Best method of repairing the cool fuel module in question is removing it from the engine assembly and placing it on the bench

In order to remove the cool fuel assy the motor mount needs to be loosened/removed.

To riase the engine on one side I use a bottle jack on the exhaust manifold and wood blocks to support the motor. Remove mount/cool fuel assy as needed.

Your situation looks tight, not gonna be fun but hopefully you proceed safely

 

[alldodge]

WADR - Motor mount doesn't need to be removed.

The bracket that holds CF module is held on by 2 motor mount bolt studs. The nuts and washers are removed which releases the bracket that holds CF module.

 

[dubs283]

Motor mount doesn't need to be removed

Not always

Based on OPs pics I took a shot on removing the mount. Might work that they don't have to go that route

Worked on a couple boats that I had to remove the mount, pics looked familiar

ymmv