Engine Trouble - 2001 Yahama OX66 Saltwater Series 250hp

[FlyingWhale]

I recently had my annual engine service - new filters, plugs water pump, impeller, lower unit fluids and this time a fuel injector cleaning. After the service I started the boat up for a test run. When shifting into forward I noticed it was very difficult to shift and when trying to go into reverse it was quite hard as well. I had the mechanic check it out and his assessment was that the idle was higher due to the injectors being cleaned and he just needed to lower the idle. He did this and it shifted better but not quite as easy as before the service. When testing it again, as soon as I reached 3/4 throttle the engine would just shut down. I was able to get it restarted and made my way back to the dock at low rpm. The mechanic check it again and found the fuel pump diaphram had cracked. I had him replace all 3 with new ones. Back into the water hoping all is now well, but RPM at WOT would only go to 5100. Normally the engine runs up to 5600 fully trimed. Additional testing indicates the #5 cylinder is not firing at any RPM. We are unable to diagnois why. Any suggestions as to what might be causing this would be greatly appreciated.

 

[seasick]

Bad plug wire perhaps or a defective plug would be the best you can hope for.

 

[grady23]

?? How was the boat shifting and running prior to the mechanic "working on it" ??
Did you observe any fuel in the water when idling at the dock?? -- Leaking pump diaphragm
Sounds like a possible bad coil that's breaking down under heavy load or fuel starvation problem.
Be SURE that all plug wires are connected at BOTH ENDS.

 

[FlyingWhale]

Thanks for the replies. The engine ran great prior to the service. I did experience a spun hub on the prop and just went ahead and had the service done while the hub was being repaired. I change my fuel and fuel/water seperator 2x a year. I only use valvetech gas which is 100% gas and add ringfree to each tank. The boat id dry stored when not in use which averages once a month.

 

[uncljohn]

I don't think 5100 rpms is too slow. My 2002 OX66 tops at about 5200 rpms, but I never go there.

Let us know what you find out!

 

[gw204]

Hard to shift as in the throttle was hard to move or the throttle moved fine, but the engine wouldn't go into gear and would grind? If the latter, then I would believe the idle speed diagnosis.

Disconnect the shift/throttle cables at the motor end and see if if the throttle is easier to move. How old are the cables? Check all electrical connections that would have been manipilulated (plug wires, injector harnesses, etc.) and try swapping the non-firing plug to a different cylinder to see if the problem moves with the plug.

Also, check to ensure all your filters are on tight. An air leak could induce a fuel starvation issue.

 

[Gary M]

With all the servicing you mentioned, I didn't see anything about the O2 Sensors being cleaned. Did you have them cleaned?