Engine Sputters

[chadcohn]

New guy here.

I have a 2010 Mercury Optimax 90 2 stroke that will not allow me to run WOT. As the boat begins to plane the engine starts sputtering. It appears that this happens around 3000rpm. I have had the motor checked over several times to no avail. Fuel & air pressure are good. No water in fuel and again fuel is being delivered adequately and properly. Motor starts and idles with no issues it's only when trying to run WOT. Last mechanic stated that he believes it is electrical. Changed the plugs recently and ensured all boots were secured properly, check fuses (I could see easily) and tried to ensure all grounds were tight (again the ones I could see). I have had the injectors cleaned and flow tested, fuel lines are all new as well. I'm at a loss, mech said the motor works fine it's something is cutting out and not allowing the engine to run WOT. I have video of it as well.

Any ideas/suggestions would be greatly appreciated.

Engine S/N - 1B736961 I

Thanks,
Chad

 

[GA_Boater]

Welcome aboard.

Has your mechanic pulled codes from the ECU?

 

[chadcohn]

He checked for codes and said the crazy thing is there are none when it is sputtering and subsequently stalling. There were some older codes but nothing for this issue.

 

[chadcohn]

Here are the codes that were pulled that he said were old codes.

 

[chadcohn]

So the battery switch appears to be good, alternator connections are good but I cleaned them anyways. Battery terminals are clean. I looked at every fuse block I could find (on the motor) and no fuses are blown. I'm still working through the connections in the console. FTR, Mako wiring is the absolute shittiest I have seen. I think rats would run from the nest that it is, so I'm trying to clean it up while I'm at it. I'm going to replace the filler hose and vent hoses tomorrow assuming I don't run out of daylight again. So far all connections I have looked at appear to be in working order and dry. Going to look at the sending unit as well and ensure everything is tight and clean. Batteries are out and I'm going to charge them individually and check the voltage on them too. I'm considering replacing the battery switch but haven't decided yet because I don't necessarily want to swap out good parts...yet.

 

[Chris1956]

My neighbor had something similar with his Optimax. It turned out that the "door" that was supposed to open in the aux fuel pump was stuck closed. It starved the main fuel pump and the motor for fuel.

 

[chadcohn]

Crazy thing is the fuel & air PSI are steady where they need to be, mech ran it on the dyno to replicate it having a load on it but definitely something to check.