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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10594
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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Have 1990 454 with silent choice.. does not seem to be

Customer Question

Have 1990 454 with silent choice.. does not seem to be getting power.. does not work. How to test
Submitted: 1 month ago.
Category: Boat
Expert:  Jason replied 1 month ago.

Hi Rich, my name is Jason.

Is this engine a Mercriuser, Volvo, OMC or something else?

What is the history on it, have you ever personally seen it make full power?

Customer: replied 1 month ago.
It is mercruiser and first owner.. it use to work two years ago before winterizing.. have the unit off here.. can this be bench tested
Expert:  Jason replied 1 month ago.

I'm a bit confused. Are you trying to troubleshoot an engine that is not making power or are the exhaust diverters not switching back and forth?

Customer: replied 1 month ago.
Jason, Sorry for delay..only have computer at work. This unit is air operated, holds open exhaust struts for open exhaust. When switched with toggle switch, the air lets out and struts close for thru lower unit exhaust. Trying to bench test unit to see what part is bad if any.
Expert:  Jason replied 1 month ago.

No problem. I'm not familiar with the pneumatic style diverters, I will opt out and leave this open to the community.

Expert:  Tan replied 1 month ago.

Hello Rich. My name is Tan.

Have you checked for voltage at the switch and then the air pump? On the switch you need 12 volts to the center terminal purple wire. Do you have voltage? Then you should flip the switch on one direction or the other. The brown wire turn compressor on and the gray wire activates the solenoid.

Customer: replied 1 month ago.
Hi Tan, Only have computer at work so I can't respond right away. Checked voltage at the pump before removing from boat which is 150 miles from here, there is power at the red wire on pump.. center terminal. Is there any way to bench test this without being on boat?
Expert:  Tan replied 1 month ago.

Yes apply 12 volts to the red and black wires going to the motor of compressor. 12 positive to the red and 12 negative to the black.

The compressor should run and produce air at the fittings.

If it runs then the compressor isn't the issue it will be in the wiring going to the compressor and solenoid. You must have ground and 12 volts fore it to run correctly. Ground all the time and voltage when applied from switch.

Customer: replied 1 month ago.
Can I use a battery charger to test and which black wire... guessing the one on the end
Expert:  Tan replied 1 month ago.

You can try the charger it might work. The center terminal is the ground for both the solenoid and the compressor motor. The red is the motor wire and the terminal to the far right is the solenoid motor. The way it works is you flip the switch turning the compressor on pushing the silent choice flaps open then you push the switch the other way which activates the solenoid dumping the air holding the flaps open causing them to close.

Customer: replied 1 month ago.
Thanks, ***** ***** will get a battery and put the neg to the middle post and pos to red on left for comp and then put pos to the right post for sol.... if the comp runs its ok but how to test solenoid. If I get a toggle switch with 3 term, how to hook it up
Expert:  Tan replied 1 month ago.

The only way to know if the solenoid works is when the compressor build pressure and holds the flaps open then apply voltage to the solenoid the flap should close.

The switch is connected with 12 volts positive to the center terminal then the wires coming from the solenoid and the compressor to the other 2 terminals.

The other possible issue you could have is a failed diaphram in the compressor or an air leak not allowing the system to build pressure. There is also a pressure relief valve that could be failing and not allowing the system to build pressure. You won't be able to test any of this till system is reassembled and you can check for air leaks. To test for air leaks you will need a spray bottle of soapy water. Spray all connections look for bubbles.

Expert:  Tan replied 1 month ago.

Please don't forget to positively rate my help as that is the only way I get credit for helping you.

To rate click on the stars at the top of the page 3 or more.

Follow up questions are always welcome.

Thank you........Tan

Customer: replied 1 month ago.
If the comp motor is bad, any help on where to get one

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