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

[Fernando Perez]

Look for the ecm and find the lines. Dont have pictures, the code can be many other things.

. Good luck. 

[MIGUEL MENDEZ]

Hello Fernando I am having the same code problem and 559 do you have some pictures about the ecm line fix?

[Andrew]

I am having a similar issue and need to order a few test gauges. Can someone tell me what thread size I need for a vacuum and a pressure gauge for a 2006 qsb 5.9-425?
Thank you,
Andy

[Jim Clark]

Dont suppose you have a picture of the line that was loose? I have the same issue.

[Tony Athens]

Fernando,

Glad you stuck it out.. Good job.. I’ll remember this..

Tony

[Fernando Perez]

We finally found the issue, the fuel line fitting for the ecm cooler was loosed enough to allow air into the fuel system, but never leaked.

Thanks all for the great help.

[Luke Nelson]

I have almost the same thing but on a pair of 24V qsc’s, I did almost the as what you have done . I found a way around it (not the right way, but it works 600 hours down) but It will good to hear is you find the right solution.

It should not matter I had more issues with the engine I had the remote fuel filter kit on as it had more piping to run through?

[Fernando Perez]

Yes, mine looks just like the one in the picture.

[Tony Athens]

9 VDC at the pump does not sound right.. Pump may be running at 50% or less.

Look at the picture–Does you engine ECM side look like this with the 2 power plugs?

Tony

[Fernando Perez]

Hi Tony,

Checked all supply and return lines, also the engine tubes and all is free of restrction. I have not done the external pump test yet, wile checking the tubes we tested for voltage on the electric pump plug and only got 9.1 volts, so we tested the othe engine and same 9V. Is this normal? ECM is getting 13.2.

Thanks a lot for your help!

[Tony Athens]

Sorry, but your post was not clear.

Next–You are not getting fuel–why? Don’t know yet.

The GPH reading thing make sense as the ECM advances the throttle internally to try and compensate so the gauge reading goes up even thought the actually GPH does not.. Until you solve the low fuel pressure issue, nothing is going to work right.

I think the only thing you can do now is to install a external elec pump on one engine that can supply about 10 PSI at about 30-40 GPH .. Put it close to the engine and test it pumping into a 5 gallon receptacle first to see if it can pump close to 5 gallons 10 minutes.. Watch the vacuum gauge while pumping. If it seems to pump well, then hook it up to the engine and test with it on. Watch your fuel pressure gauge on the filter head while running.

FACET makes some good pumps for this..

Curious–Where is the level in the tanks in relation to the fuel inlet on the engine (vertical elevation)? When your tanks are full, can you start a siphon at the engine fuel connection?

Also, blow thru your return line to be sure it is non-restricting to return flow.. If you use more than your breath to initially clear it, have the fuel fill cap removed. After clearing, you should be able to blow thru it easy.

If nothing improves, disconnect the fuel lines coming from the tanks, remove the fuel tank caps, use an air compressor to back blow the lines and fuel pick-up into the tank–You hear lots on bubbles when you do this.

The test again.

Tony

[Fernando Perez]

That was me tensting the gauge by sucking on it. I was able to move it all the way to 15”.

[Tony Athens]

What am I missing”” The gauge I am looking at shows 15″ Hg ( vacuum)..

Tony

[Fernando Perez]

Tony- re -did test and same results. 2” max of vacuum. See attached pic, is odd that the port engine is drinking 1 additional gallon of fuel compared to stb.

[Fernando Perez]

I Think I had an airleak on the fittings, will fix and retest.

Thanks,

Gauge seem fine

[Tony Athens]

Are you sure the gauge is accurate? If you suck on it, it should move above 10″ HG pretty easy. Test it that way. Post a pic of the gauge.

Tony

[Fernando Perez]

Hi, did vacuum test and all seems fine. Pointer will never pass 2” in vacuum, same with vacuum gauge isntalled on racor. Can it be a return line issue?

[Fernando Perez]

Thanks, will do and report back.

[Tony Athens]

Low Fuel pressure QSB 5.9

Your alarm is simple–Your Fuel pressure is way under spec.. It’s find the “why” that will take some effort…………..

1) Look at the picture.. Get a good 0-15″ or 0-30″ HG vacuum gauge attached to the test port on the fuel block..

I suspect this will show the issue–Your engine cannot get fuel from the tank..

Get me numbers..

Tony

[Fernando Perez]

There is no noticeable rpm pattern, most likelly at WOT, it some times activates when power is increased (ex 1,400rpm to 1,600 rpm), also when boat is riding in same direction as the wave and slows down due to the big wave in front, as soon as the engines start pushing harder it activates.

[Author]

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