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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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I have a 94 mercury 40 hp oil injected outboard. Worked fine

Customer Question

I have a 94 mercury 40 hp oil injected outboard. Worked fine in the fall. I tried to start it today and when I turn the key no warning sound/alarm is heard. The motor does start, but only at a very low ideal, The motor is not responsive to any throttle commands? What do you think?
Submitted: 5 months ago.
Category: Boat
Expert:  Tan replied 5 months ago.
Hello Josh. My name is***** are a number of things that can be wrong. We need to start with a spark and compression test to eliminate these as a [possible cause of your issue. If these check good then we can move on to the fuel system.The spark must jump a 7/16" gap on a spark gap tester on all cylinders or you can start the engine and remove the spark plug wire from each cylinder. The engine should drop rpms on all cylinders. Then we must verify the compression you should have 90+ psi on all cylinders. Do these checks and post back with findings. I will need the engine serial number also to know what engine you have exactly.
Customer: replied 5 months ago.
Great, I'll do that and get back to you.
What are your thoughts about no buzz/alarm when you turn the key to start position prior to starting the engine?
Expert:  Tan replied 5 months ago.
This is most likely a failing buzzer. The key on is a self test to be sure the alarm works. All you can do is test for voltage at the alarm. If it has voltage and it still doesn't function the alarm is bad.
Customer: replied 5 months ago.
The spark plugs are okay, I don't know how to test for compression of the cylinders. Today when I went to try and started it turned over for about 10 seconds and then nothing. The battery voltage is good. The starter doesn't pop-up and I hear a single click from inside the electrical box. The upper right corner.
Expert:  Tan replied 5 months ago.
Do you have a voltmeter to do some voltage tests? The clicking is the start solenoid. You have either a bad solenoid or low voltage to the solenoid or possible bad starter. We need to test the voltage at the solenoid and the starter with key in crank position.
Customer: replied 5 months ago.
I do have a voltmeter. How do I test each? And could this have caused my initial problem of the motor not being able to change RPMs?
Expert:  Tan replied 5 months ago.
Check the voltage at the battery cable connection on the start solenoid with key in crank position. What is your voltage reading? The if you have voltage there check the voltage directly on the starter terminal where the cable comes from the start solenoid. What is your voltage reading?No this will not affect rpms. Fuel, compression and spark affect rpms. We need to check spark on all cylinders then do a compression test. To do a compression test you will need a compression gauge. Then remove the spark plug install the compression gauge on the top cylinder crank engine what is the number on the gauge? Do this test on all cylinders.
Customer: replied 5 months ago.
The starter solenoid goes from 12.4 to 0 in the crank position. I can't find the wires that go into the starter, must be on the medial side of the starter, but the start was working okay. Is the solenoid function correctly?
Expert:  Tan replied 5 months ago.
You are loosing voltage to the starter. You have a bad battery cable, cable connection or cable end. Check all the battery cable connections on the battery and the engine. Check both positive and negative cables. Post back with findings. We can try to determine which cable is the issue by testing like this connect the black test lead to the negative post of the battery and the red test lead to the battery positive on the solenoid. Now turn key to crank position what is your voltage reading?

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