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Outboard Guy
Outboard Guy, Marine Mechanic
Category: Boat
Satisfied Customers: 66
Experience:  Certified Mercury Outboard Tech. - 8 years experience
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I have a 2006 Merc 90 hp optimax. when I first run the boat

Customer Question

I have a 2006 Merc 90 hp optimax. when I first run the boat i will run great for about 5 - 10 minutes at 3500 rpms. Then the engineen start to stall out, if I back down the throttle it will idle fine and not stall. I can run the enginee all day at 2000 rpms and lower, but when I try give it gas after that first time is stalls out it will immediately start to stall out.
What is problem?
Submitted: 7 years ago.
Category: Boat
Expert:  Outboard Guy replied 7 years ago.

I believe there is a service bulletin on that motor that requires the replacement of the 3 coils. There is no charge for this, even if the motor is out of warranty. Take it to your local Mercury dealer and they should be able to take care of this.


I'm not sure if this will solve your problem, but I certainly wouldn't go any further without doing this.

Outboard Guy and other Boat Specialists are ready to help you
Customer: replied 7 years ago.
I spoke with the service dealer and the that service bulletin does not apply based on the serial number of my engine. What I'm being told is that the theroy behind the failure might be the Lift pump but the mech isn't sure. The pressure gage that they are using to test the hight pressure full pump only goes to 60psi and the high pressure pump for engine runs at 110psi so they can't really see what is going on. They think that becuase the boat will run for a while at first that the problem is not the high pressure pump and is more likely the lift pump that runs at 30 psi. he as been in contact with mercury service people several times. They suggested to checks some type of screens in the engnie to see if they are clogged. But to me and the mech that doesn't make sense to how the engine is behaving. any thoughts?
Expert:  Outboard Guy replied 7 years ago.
Ugh, I'm working on two 115's now that are having crazy performance issues. One runs at WOT but dies when backing down, the other won't run over 2500 RPM. I went ahead and changed the coils on both motors since that was a factory freebie. I pulled the injectors on one of them late today and they were black and loaded with carbon. I'm going to drop them into the carb cleaner tomorrow morning. I'm hopeful that's the problem. I spoke to Mercury and they said that if that doesn't work, it's going to be a new wiring harness and finally a new ECM.