MerCruiser Cranks but Wont Start or Hard to Start 5.0L MPI 350 MAG MPI MX 6.2

Models these procedures apply to:

Sterndrive (MCM)

5.0L MPI Alpha and Bravo, 350 MAG MPI Alpha and Bravo, 350 MAG MPI Alpha and Bravo Horizon, MX 6.2 MPI, MX 6.2 MPI Horizon

Inboard and Tow Sports (MIE)

350 MAG MPI Inboard, 350 MAG MPI Horizon Inboard, MX 6.2 MPI Inboard, MX 6.2 MPI Horizon Inboard, 350 MAG MPI Tow Sports

Year models these procedures apply to:

2001 2002 2003 2004 2005 2006

Important Information

1. Fist figure out what engine system is causing the issue. For an engine to work, basic needs must be present, spark (ignition), fuel and compression for the engine to operate. If one of these three components are not present or not functioning correctly, the engine will not run.
2. If possible, use a diagnostic tool to determine if faults or codes are present. If codes or faults are found, fix the issue before continuing. 
3. Check and see if fuel is reaching the Schrader valve which is located directly behind the throttle body.
4. Extract the spark plugs, ensure the proper heat range, type and the spark plug is being used and is not burned, fouled or oil contaminated. 
5. Perform a compression test on the motor and make sure the motor is mechanically sound. 

Engine cranks over but will not start or starts hard

Causes

1. Flame arrestor possibly clogged or blocked.
2. Fuel pump pressure is excessive.
3. Fuel tank is empty.
4. Fuel shut off valve possibly closed.
5. Vapor lock.
6. Lean fuel system.
7. Gasoline grate to low or stale, sour fuel.
8. Fuel contaminated with water.

Action

1. Clear and clean the flame arrestor.
2. Inspect for the cause of the excessive fuel pressure, repair as necessary.
3. Add fuel to the fuel tank.
4. Turn the fuel shut off valve to open position.
5. See repair manual for vapor lock condition.
6. Clean and clear the fuel system.
7. Drain the fuel from the tank and refill.
8. Use fuel treatment to remedy the contaminated fuel. If the issue continues, drain the gas from the fuel tank and refill the tank.

NOTE: Never attempt to service your MerCruiser without a factory service manual to help guide you through service procedures. 

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