mercruiser 350 mag mpi horizon bogging down under load

[arcane808]

Aloha everyone,

Thank all you guys for a wealth of knowledge. It is really appreciated!

So as the title says I have a 2006 350 mag mpi horizon model with about 750 hours on it and a bravo leg. Ive had a problem that apeared slowly and has gotten progressively worse every time I go out. Starts right up and runs nice at lower rpm's but when I head out the motor starts to bog and re-surge back and forth starting around the 2800 rpm range. It may drop as much as 1000rpms before re-surging. It sounds fuel starved to me. The problem Starts out bad then slowly tapers off with smaller and smaller fluctuations in throttle until its running perfectly. Its been taking about 20 in the morning before she runs perfectly normal for the rest of the day without incident ( i usually go out for up to 12 hours or so).
Ive read many other threads that sounded similar but my issue does not include any stalling or backfiring like the other threads Ive found. however those other threads talked a lot about the fuel pump being the culprit. I do clearly hear it prime before I turn the key over.
Things Ive tried already
1. replaced all the fuel (I use marine stabil at every fill anyway)
2. Replaced fuel filter twice (cool fuel gen III)
3. cleaned flame arrestor (little foam thing)
Other observations
1. Problem is only under load. When in the water in neutral throttling in that rpm range is smooth and trouble free.
2. fuel tank air vent is clear
3. vital signs at idle: engine runs at 168f, fuel pressure steady at 42.8, water pressure at 3.7, oil pressure 49.1

One Friend of mine suggested maybe air could be leaking into fuel line making trouble until they are warm enough to expand and close off leaks. Another friend tells me to replace all the plugs, cap and rotor. Not sure what else to try at this point..... help? : )

 

[alldodge]

Howdy

Does the fuel pressure stay around 40 psi though out the rpm range?

Have you checked your anti-siphon valve on the tank? The valve is a spring loaded check ball where the fuel line connects to the tank. This valve can get gummed up and start sticking.

IMO, your wasting your money using stabil, your not hurting anything

 

[scoflaw]

Have you addressed the flaking paint issue associated with your cf3 ? Pull off the FPR that's attached to the module ,see if it's got paint flakes on it. If this is a salt water boat the whole unit could be corroded on the inside. Not uncommon, paper thin wall that separates the fuel from the water jacket. POS design

 

[arcane808]

thank you guys for the reply, those are going to be top of my list for things to check next. Going to take the boat out to check the fuel psi while my issue occurs. That anti siphon valve is pretty inexpensive, If i'm going to take it off to check it I might as well put a new one on. And yes its a salt water boat so im gonna check for those paint flakes right away too!

 

[alldodge]

The issue is with certain serial numbers. Its on a Merc bulliten below but does not talk specific paint issue but calls out corrosion

http://www.mercruiserparts.com/bulle...2009/EN_01.PDF

 

[arcane808]

Ok so went to the boat today and found a ton of paint flaking off under the FPR. My engines serial is 0w062069, so if that bulletin reads the way I think it does then ive got one of the defective units. The paint is coming off in larger dime sized flakes. didnt see anything particulate size. Did a bit of reading on this issue and seems like there is a lot of sour people out there over this one. Needless to say I did not take the boat out to check the fuel psi, dont want to do anything until that module is cleaned or replaced.
So at this point its damage control. Is it worth it to clean the unit out and remove all the paint myself? If I did that can I still use the high and low pressure pumps or is it likely they are ruined too? Or is it better to just replace the whole thing? And more importantly how likely is it that the paint has made it to the injectors? Since there was paint under the FPR does that mean its for sure made its way further into the fuel system? If its made it to the injectors would my symptoms be temporary for the first 20 minutes of use (like ive been experiencing) or more likely to be a constant symptom?
I guess I can just start with the the module then take it out for a run. If I still have a problem then its further into the fuel system.

 

[alldodge]

IMO if everything is cleaned out, fuel pumps and internal filters, lines and fuel rail flushed, then clean the injectors (professional cleaning, about 20 and injector), then you should be good. The issue is the paint that came off can wind up anywhere in the system from the pump module to the injectors. It can be fixed, the issue is just how far one has to go to make it clean

 

[muc]

0W062069 comes up as a 2004 engine that has had fuel pump done twice already. Also has an open recall.
Suggest you talk to your dealer. If that is your serial number.

 

[scoflaw]

New unit is in the 1K range. I fixed mine on the cheap by glass beading all the paint off the cover. Then I used the POR 15 product on the cooling jacket and also replaced the o ring hose connectors with the screw in style.. Less than 50 bucks and that was 3 years ago. There is also another filter on the rail that you should clean as well

 

[arcane808]

Thanx for all the great advice guys, looks like I have a lot of work to do. Ill call my shop about that open recall too (shoudlnt they have said something the last five times ive brought it in). First step that cool fuel is coming off today!

 

[Jncsk8r]

Sorry to bump this from 2016 but I have a 2004 Mercruiser 350 mag mpi doing the same thing, sometimes more severe than others. Was wondering if you ever found a solution.