Electrical Issue? Merc 350

dewey9

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Joined
Aug 6, 2008
Messages
4
Hi everyone,

Been having an issue with my boat. Basically whats happening when up on plane at crusing speed to WOT if you hit the trim button to try and bring the trim up or down a little bit it creates a hesitation or skip or something in the motor while the button is pressed. When you let the button go it goes back to running fine. Seems electrical to me as the battery gauge goes down when you hit the button and returns to normal after you release the trim button. I'm thinking its an arc or short somewhere? It also doesn't do it all the time either. Seems like only when the engine gets warm (150 degrees or so I believe) and it doesn't do it at all at slow speeds regardless of engine temp. The engine is a 96 Merc 350 I/O with Alpha I outdrive. It has all new spark plugs, cap, rotor, and plug wires done at the end of last year. Any thoughts on where I should start? Battery cable connections? Bad Coil? Thanks!!
 

JustJason

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Aug 27, 2007
Messages
5,327
Re: Electrical Issue? Merc 350

The first thing I would look at is tracing where the trim pump is actually getting its power from. If it's getting power from anyplace in the ignition system then your going to have problems. It should be getting it's power, more or less, straight from the battery.
 

dewey9

Recruit
Joined
Aug 6, 2008
Messages
4
Re: Electrical Issue? Merc 350

The trim pump doesn't get its power from the ignition system. The positive cable runs from the battery to the starter then from there over to the trim pump. Again, thoughts?
 

JustJason

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Aug 27, 2007
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5,327
Re: Electrical Issue? Merc 350

Do you have a digital multimeter?
 

dewey9

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Joined
Aug 6, 2008
Messages
4
Re: Electrical Issue? Merc 350

Yea I do. I did check the resistance of the coil last night as well. Primary was bouncing between .6 and .7 ohms (spec = .6-.8 ohms) and secondary gave me 10,500 ohms (spec = 9400-11700). It was pretty oilly when i went into the center pole. Is it normal to see the oil like that? should I be checking these numbers again after the engine and coil have warmed up? I took all the readings cold. What else would you recommend checkig with the meter?
 

Bondo

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Apr 17, 2002
Messages
71,241
Re: Electrical Issue? Merc 350

Ayuh,... Sounds like the trim motor is Dying,+ drawing Too many amps....
Or,...
Possibly Bad motor Grounds...
 

JustJason

Vice Admiral
Joined
Aug 27, 2007
Messages
5,327
Re: Electrical Issue? Merc 350

put your positive lead on the stud of the trim pump that the power wire connects to, put your negative lead on the starter stud that the other trim pump power wire lead connects to. Put your meter on vdc. If it's not autoranging then 6 volt scale if you have it. Start the engine up. Then run the trim pump up and down. whats your reading on the meter?
The other thing you can to involves an amp clamp to check for current draw by the pump.
 
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