Engine running rough under load

[Maverick]

After a frustrating season last year and lots of £££'s (new leg, risers etc etc) was running great when returned from Tech.  As soon as I take her out 2 weeks later, fine at tick over but as soon as put under load running very rough , popping and smell of unburnt fuel.

Tech connected computer this week, under all conditions and no faults shown.!

Has anybody else had this, or have any ideas, I can't face another season like the last one!

Power is Mercruiser 260 5.0 mpi new Alpha One leg.

[gslpro]

Well, the first thing I thought to myself is you might want to get a tech that is a mechanic first, computer tech second.  This could be several things, but they are all arbitrary without seeing how the engine reacts to different scenarios.  Vacuum lines or a leak could cause this issue, fuel filter or fuel line blockages, your pressure rail for the fuel injection, valves or cam issues....etc..  The list goes on, but that is why mechanics actually go to school.  Have your guy put down his computer for a minute and look at the engine with a mechanic's eye.  Or best bet...go find the older mechanic sitting inside with the greasy hands. They usually know their stuff more than the laptop techs. 

of course, just my opinion.  I wish you good luck on it being a cheap and quick fix.

[Maverick]

I agree with that! I liked the way that even when the engine is messing around he tells me there are no fault codes!....

[RAPID]

Maverick. I had a similar problem last spring with my 2004  342. Boat ran fine in the slip but the starboard engine ran very very rough under load. After numerous attempts to find the problem my mechanic noticed that one of the electrical connectors hidden behind the fuel pump had wiggled loose. Took it apart , cleaned the ends and zip tied it together so it would not work itself loose again. Worked like a charm.  Had the same problem during the summer on the port engine during a day out. This time I knew what to look for. Same issue. Same fix.  Good luck

[Maverick]

Thanks Rapid, got my mechanic to test all connections and he wasn't happy with the distributor cap. Just waiting for some calm weather to put her under load! Fingers crossed this is my one inexpensive fix over the past year!