Code 559 low fuel pressure – accelerating

[Fernando Perez]

Hello,

Ive been trying to solve the 559 low fuel pressure alarm for some time now with no results. Right now it only activates when power is put to plane and when WOT.

Boat has a pair of 5.9 QSB 355 hp 650 hrs 2007

Here a list of things done with no sucess in order:

1)Replaced racor. (Issue improved but still present)

2)Replaced engine fuel filter and vacum gauge on racor)

3)Replaced pressure sensor on fuel rail.

4)Replaced fuel transfer pump (electric pump)

5)Replaced fuel regulator (the one attached to the HP pump)

6)Did a sea trial with mech and at WOT port engine would do 2,730 RPM and stb 2,800. We also noticed the fuel burn was similar below 1,000 rmp the port would burn .8 GPH more that stb and after 2,500 rpm they will burn similar again. No smoke anywhere to be seen.

Mech connected the lap top and said inyector cyl 1 & 6 where not causing (some noice would go away) changes when turned off at Idle, so they where for testing, they passed all test perfectly.

The mechs are sratching their heads with no future plan at this moment.

Please help.

BTW, I bougth Vessel View 502 convertion from SBMAR and is doing great, I was also able to connect my Garmin and now can see en engines.

Thanks

Topic

[Corey Schmidt]

Given those numbers while testing… at what point / RPM did you see the fault code appear?

[Fernando Perez]

Ok, installed the guage and here results.

Port Engine (issue engine)
Idle-13psi
Load 1,600 rpm -7psi
Load 2,050 rpm -5psi
Load 2,730 rpm -1psi

Starboard Engine
Idle-11 psi
Load 1,600 rpm -8psi
Load 2,050 rpm -5psi
Load 2,800 rpm -3psi

Please let me know how you see them.

[Fernando Perez]

Will do and report back. thanks!!!

[Corey Schmidt]

Fuel pressure…

In order to take the right measurements… I would install a 0-30 in. vacuum gauge as close to the engine as possible to see if you’re seeing any restriction on the supply.

Also, I would install a 0-20 PSI pressure gauge on the fuel filter head to see what kinds of pressures youre seeing there.

Fuel Pressure Test Port

[Luke Nelson]

Is it both engines or just one?
If its just one can you cross the fuel lines?

[Fernando Perez]

Hi Corey thanks a lot for the help.

Please see responses:

Do you hear the lift pump turn on and run when you turn the key on to IGN? ——— YES———-Have you replaced the LIFT PUMP? ——- YES NEW——

Do you have any valves on the fuel RETURN circuit? —- YES , ONLY ONE AT THE FUEL TANK, FULLY OPEN—-

Are you getting AIR into the fuel system? —— DONT THINK SO, HOW CAN I CHECK AND CONFIRM THIS—-

[Corey Schmidt]

Troubleshooting…

This kind of fault can sometimes be tricky to solve as there could be many culprits.

Causes of this fault code include the following:

• High inlet restriction
• Excessive air in fuel
• Loss of fuel prime during cranking
• Plugged fuel filter
• Low lift pump pressure
• Stuck or restricted electronic fuel control actuator
• System return (excessive return flow from the injector, high-pressure pump, or rail pressure relief valve)

Questions:

Do you hear the lift pump turn on and run when you turn the key on to IGN? Have you replaced the LIFT PUMP?

Do you have any valves on the fuel RETURN circuit?

Are you getting AIR into the fuel system?

[Fernando Perez]

Steve, thanks for the help. The engine has very good power, the alarm only goes on at WOT and when accelerating to plane (once stable it goes away).Also, the engine is reaching 2,730 RPMs and the vacum gauge on the Racor is reading less than 5, so dont think there is a blockage issue.

What can it be?

[Stephen Oliver]

Probably far too simple have you checked your fuel pick up in the tank? could be partially blocked with debris / dirt? Also have you checked your breathers are clear on the tank, i doubt it would be this as my previous experience with this happening caused the engine to cut out due to the filter emptying..

Steve

[Author]

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