2003 Mercury 90HP 4 Stroke Grounds

[Vwsandcar]

I have been having intermittent run ability issues with my outboard. Intermittent lack of power and every once in a while bog on acceleration. It could be 5-6 outings between issues and generally the issue will only occur part of the day. I was looking at connections and grounds tonight when I noticed 2 grounds were connected to the bracket in the picture and one to a bolt on the regulator. I moved all the grounds to a threaded hole on the block. In the FSM it appears this is where they go but it’s not clear. Can anyone reference their engine and confirm if I’m correct or not? The pictures are after I moved the grounds and of the FSM

 

[dingbat]

I have been having intermittent run ability issues with my outboard. Intermittent lack of power and every once in a while bog on acceleration. It could be 5-6 outings between issues and generally the issue will only occur part of the day. I was looking at connections and grounds tonight when I noticed 2 grounds were connected to the bracket in the picture and one to a bolt on the regulator. I moved all the grounds to a threaded hole on the block. In the FSM it appears this is where they go but it’s not clear. Can anyone reference their engine and confirm if I’m correct or not? The pictures are after I moved the grounds and of the FSM

Ground is ground unless the connections are compromised in some way. Only in systems giving specific ground resistance specification do you worry about it.

As a test, put your volt meter on ohms. Check the resistance between the old connection point and the new connection point.

 

[stresspoint]

moving the ground wires to the correct place was a good move , however i doubt that is your issue.
im guessing you have a dodgy coil .quite common on that model motor and Yamahas with the same PH.
the coils are connected to 2 plugs so when you loose a coil you get no power to 2 cylinders intermittently , also change out your spark plugs , they don't last forever on these motors.

 

[boscoe99]

What is meant by FSM?

 

[boscoe99]

Yamaha Service Manual depicts the block being the ground point. For multiple components. One of which is the TPS. I can envision an intermittent ground causing all sorts of mayhem.

 

[stresspoint]

What is meant by FSM?

factory service manual.

 

[boscoe99]

factory service manual.

Never heard that term before.

Now I am wondering what factory? If someone is asking about a Mercury branded motor made by Yamaha does the "factory" mean the Yamaha factory where it was made (Yamaha Service Manual) or does it mean Mercury who only sold the motor (Mercury Service Manual)?

 

[stresspoint]

Never heard that term before.

Now I am wondering what factory? If someone is asking about a Mercury branded motor made by Yamaha does the "factory" mean the Yamaha factory where it was made (Yamaha Service Manual) or does it mean Mercury who only sold the motor (Mercury Service Manual)?

you would use a Mercury service manual , the actual power head and some parts are Yamaha , but many of the ancillary items on the motor are Mercury specific. The mercury manual covers everything you will need for that motor.