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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10806
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have a 1987 4.3 sunbird boat with cobra outdrive, engine

Customer Question

I have a 1987 4.3 sunbird boat with cobra outdrive, engine runs normal till the trim is used and then pulls down to around half power.
Submitted: 2 years ago.
Category: Boat
Expert:  Tan replied 2 years ago.
Hello. My name is***** is usually cause by a poor battery connection in the power trim. Check all the battery connections on the power trim.
Customer: replied 2 years ago.
I've tryed that and can't seem to find a loose or corroded conection.
Expert:  Tan replied 2 years ago.
Try routing the trim battery supply directly to the battery if it isn't already. Does the trim motor sound labored when trimming engine off?
Customer: replied 2 years ago.
trim works fine when used with just battery when the engine is off.
Expert:  Tan replied 2 years ago.
Can you move the trim battery and ground to the battery directly?
Customer: replied 2 years ago.
It works fine when just the water boot is used before going in the lake but when moving in the water things change.
Expert:  Tan replied 2 years ago.
That's because there is no load. With the age of this engine the wiring builds resistance. Resistance is cause by corrosion in the wiring. When you hit the trim the resistance in the wiring causes the trim to steal voltage from the ignition system causing the engine to loose power. Moving the trim battery power from the engine to the battery usually solves this issue. The other option is to replace the engine wiring harness.
Customer: replied 2 years ago.
Makes sence is that the complete harness or just the one in the rear, also what about the switch in the control arm.
Expert:  Tan replied 2 years ago.
The only wires you need to move are the battery supply and the battery ground. So disconnect the red from the engine coming from the trim relay and do the same with the ground from the trim relay to battery ground. All we are doing is moving the trim power supply from the engine to the battery. That way it doesn't stress the ignition system on the engine. The rest of the trim wires stay the same. In later years they wired the trim directly to the battery just for this reason. Do you follow what I am saying? Post back with questions.
Customer: replied 2 years ago.
Yes thanks sounds better than the guys at the mariana are saying..
Expert:  Tan replied 2 years ago.
Post back if you need further assistance.Your welcome.........Thank you......Tan Please don't forget to positively rate me as that is the only way I get credit for helping you.

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