Help locating what caused #6 rod to break (detonate)

[speedthriller]

I have a mercury 250efi 2 stroke which detonated #6 piston. The rod broke in half. All the other pistons and cylinders look good. The shop rebuilding the motor says that cylinder definitely starved for fuel which caused the failure.


I have taken the injectors to get tested, I was present and they were all firing great. The guy doing the test bench tested them at full load, pulsing and other tests and they were all the same. I took the fuel line coming out of the tank and it is clean with no blockage anywhere. I'm starting to think something else caused this? Am I missing something? That cylinder was definitely getting fuel. I'm thinking the rod broke in half from fatigue, causing top of piston to hit head which caused piston to disintegrate and look white?


Any help would be appreciated, thanks

297941

[pointer]

Switchboxes?

Or electronic issue to the injector?

pointer

[R.grover]

Check the wiring loom plugs etc and it could all so be a fuel computer issue.
Is the complete motor apart yet? ive have the crank rings break befor and had issues take some pics of rod rest of piston and the sleve

[bobthebuilder]

Check the air injectors also as the fuel injectors spray through the air injectors.. I have also heard about this comig from not keeping the oil tank in the boat pretty much full. #6 is thee cyl that supplies the air to that tank to push the oil up to the engine.. I rebuilt one just like it last month with exact same thing happened to it where #6 got too lean and detonated and broke the rod and busted the sleeve. I have also heard of the bottom crank seal causing it.. I replaced it on the one I just did to make sure that wasn't the culprit.. Oh well in my shop here we call them OptiPop's.. but who knows what causes it? I just cover all the bases and pray over it.. Only 2 kinds of outboards exist anyway: the ones that are blown up and the ones that are going to blow up.. LOL

[XstreamVking]

That's not an opti, it's an EFI. Check both fuel pumps for delivery and proper pressure when re assembled. Also coils can double fire. Oil inj hoses putting out proper oil? etc.... How many hours?

[scc82]

Look at the pistons there are no splash ports so it is not an opti and has no air injectors. I also don't buy the low oil tank issue leaning the motor out. If a cylinder is short on air it will go rich not lean. It's was most likely a fuel quality issue or over loaded not getting full rpm or a combo of both. Number 6 cylinder are the first to detonate and stick a piston then snatch the rod out of it. I haven't seen any issues with the ignition ecms but cdms go out all the time. That cylinder could have been double firing wich could have caused the same results IMO.

Stan carson.