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My Engine Turns Over OK But It Won't Start
If your engine won't crank or turn over, go HERE.
So you know your battery is good and the starter works OK because the engine turns when you try to start it. You crank and crank and crank but it just won't run.
There are many reasons why an engine won't start. It's usually something simple.
An engine needs spark, fuel and air to run. The spark has to be strong enough and at the correct "time". The fuel has to be adequate and the engine has to have enough compression.
A good technician will first perform a general inspection of the motor and systems. A loose connection on the back of the key switch or even a bad keyswitch could prevent a motor from starting like it should.
A quick check of the carburetor will allow to confirm the engine is getting fuel. This is usually done by advancing the throttle lever while lloking down into the throat of the carb. You should see a spray of fuel as the throttle is being advanced. If the carb looks dry, it is! A closed fuel valve, a faulty antisyphon valve, a bad fuel line or a clogged fuel filter can prevent fuel from reaching the carburetor. We even have an occasional cutomer with no fuel in the tank!
A bad fuel pump can also prevent fuel from reaching the carb. Fuel injected engines are VERY fussy about fuel supply and fuel pressure. Many engines use an electric fuel pump and others use both an electric fuel pressure pump and a mechanical "lift" pump.
Electric fuel pumps can easily go bad from just sitting. The fuel turns into varnish and the pump fails. If you are going to let your boat sit for 6 months or more, you should run Fuel Stabilzer through the fuel system.
The Fuel Stabilzer will keep the fuel from ruining the fuel pump.
Electric fuel pumps make a whinning noise when they run. Most come on for about 5 seconds when the key is first turned on. If you have an electric fuel pump and you don't hear it making any noise when the key is on, you might have a bad fuel pump. You might also have a bad connection on your Oil Pressure Switch. There is an Oil Pressure Switch which keeps voltage to the electric fuel pump once the engine is running. If the oil pressure drops, the fuel pump stops and the engine shuts off as a protection feature. The switch is mounted down low on the port side of the engine block and it can get splashed with water. Unsnap the plastic harness plug from the oil pressure switch and make sure the connections are perfect.
If You Have Fuel
If you have fuel, you need to check for spark. Careful! Mercruisers have a powerful ignition system that will shock the hell out of you!
Your local Auto Parts Supply Store will usually sell a Spark Tester. Get the best spark tester they have. This is a great tool to keep in your boats tool box. Remove the main coil lead from the center of the distributor cap and install the Spark Tester. Make sure the other end of the tester is attached to a good clean ground. Crank the engine and check for spark. If you have no spark, there are several things which can be at fault.
Below is a quick list of items which can cause a "no spark" condition from the coil:
1. A bad key switch.
2. A blown ignition fuse.
3. A bad harness connection or bad harness.
4. A bad shift cable.
5. A faulty Shift Interuptor Switch on the shift plate assembly.
6. A shorted tachometer.
7. A removed or faulty Safety Lanyard Switch.
8. A bad ignition coil.
9. Breaker Points worn or not adjusted (conventional ignition).
10. A bad condensor (conventional ignition).
11. A faulty sensor (Thunderbolt or Delco).
12. A bad Ignition Module (actually very rare).
13. A bad timing chain (rotor does not turn).
In depth troubleshooting can be found in the Factory Service Manuals for your engine.
Boats can explode. Moving parts can rip your off your fingers. Hot exhaust can burn you to the bone and props can slice you up. One spark near a battery can cause an explosion. You can never be too careful. Remove the battery from the boat before working with fuel. Always disconnect the batteries negative terminal first. Clean up any spilt fuel and let ALL of the fumes dissipate before installing the battery and starting the motor. Pulleys and Belts can grab your clothes and hair. Don't wear loose clothing and keep your hair up under a hat. Always wear safety glasses. Be smart.
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