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Ask Dominick Your Own Question
Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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Jeff- 2008 Mercury 90 HP starts and runs smooth but skipps

Customer Question

Hi Jeff-
2008 Mercury 90 HP starts and runs smooth but skipps bad above 2000 rpm (? gurdaian mode). Alarm heard while runnig on plane, no obvious reason for alarm (engine temp was 140) which after one hour of runnign great during first outing of the year. fuel pressure 50.4 and impeller changeed last year, oil level fine. I changed both fuel filters yesterday and didnt improve. Any ideas for next step? Mechanic said it happened because its July 4 weekend- trying to fix myself because no one is available to look at it. No more alarms now just wont rev above 2000 without skipping.
Submitted: 2 years ago.
Category: Boat
Expert:  Jeff G. replied 2 years ago.
Can you get me the serial number of the engine?
Customer: replied 2 years ago.
Expert:  Jeff G. replied 2 years ago.
OK lets try something here. Your engine is essentially a Yamaha/Mercury hybrid. The ECM will allow you to check basic trouble codes. You can do this with a check light. If you don't have one you can make one. Go to a marine supply store and buy a LED red indicator light. The kind you would use in the dash switch panel, get one with leads a couple inches long.You will need to locate the diagnostic connector on your engine. It is a white/black and a black and a red/black wires. I don't have one of the engine here to tell you exactly where it is, should be front starboard side. Put the LED on the red/black and black see if you get blinks with the key on if not switch to the white/black and black.Note the type of terminals on the connector. Put the corresponding type terminal on the ends of the LED wires. You now have a trouble code light and is great for the tool box.Make sure the terminals are insulated and they do not touch anything, particularly each other!!!!With the LED on the connector turn the key to ON, you don't have to start the engine.If there are any troube codes the light will begin to blink. a blink, blink, blink is normal no codes.Any other codes will give a sequence such as, blink, pause blink, blink, blink and then pause and repeat is the code 13. You can only diagnose one code at a time. Once you diagnose and fix the problem turn the key off for 5 seconds to clear the code and repeat to see if there are any more codes.This will only give you stored codes which if it is the Guardian circuit should have set a code.Post back here with what codes and I'll decipher them for you.