MerCruiser 5.0 Cranks But Won’t Start


What does it mean when a MerCruiser inboard engine cranks but will not turn on and begin to run. The starter activates and the crankshaft turns over but the engine will not fire.

The battery is not damaged nor is the battery charge low. It is new battery and I had it tested. The battery terminals are free of corrosion and electrical connections are tight. The remote control lever is in the neutral position and I didn’t see any blown fuse.

I am also certain that the alternator and regulator are operating fine. What are other reasons for why my MerCruiser 5.0-liter engine will crank but does no start. Btw, it cranks healthy. It does not crank slowly, it just won’t switch on and begin operating.

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Vernon 3 years 2020-12-16T04:12:29+00:00 5 Answers 5130 views Beginner 1

Answers ( 5 )


    If a MerCruiser engine cranks over but will not start or starts hard, start with checking the basics.

    1. Use this tool and tell us what the result are..
    2. Check the flame arrestor, if it is clogged, clean it.
    3. Check the gas. Maybe the gauge is broken or someone syphoned the gas out of the tank. Fill the fuel tank if necessary.
    4. Check if the lanyard stop switch is activated and deactivate it if needed.
    5. Check for water or contaminates in the fuel system. In some instances you can treat the contaminated fuel with a fuel treatment. Otherwise you will need to drain the fuel tank and replace it with new gas. If it is full of dirt and debris clean the fuel system and tank.
    6. Possibly it has stale or low grade fuel. If that’s the case you will need to drain the fuel tank and refill it with new gasoline.
    7. Be certain the fuel shut off valve is not closed, open it if needed.

    In order to start the engine you need compression. Have you checked the cylinder compression pressure? Does the engine have sufficient spark? Get a spark tester and check for good spark.

    Best answer

    I was having the same starting problem with my MerCruiser 350 MAG MPI Horizon. I just fixed it. The fuel pump relay was bad, it even looked defective. Although you might have a carburetor model.


    I didn’t have any power at the ignition key switch. The problem turned out to be the main lanyard kill switch. So the engine cranked but wouldn’t start up.

  1. Alonso Daniel

    How do I tell if there is spark at each cylinder if I need someone to start the engine while I am in the engine bay?


      You can use a remote start switch this is a good cheap one. Simple to hook up. Then use a timing light and connect it to the main coil wire lead. If the timing light does not indicate spark when cranking the engine then it means spark was not reaching the ignition coil, likely a bad ignition coil.

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