The following information contains troubleshooting testing procedures for engine surges problems [i.e. engine surges, low or lack of top speed power, poor performance when engine is cold, engine stalls or engine misses] on the MerCruiser 5.oL, 5.7L and 6.2L MPI gasoline engines. Testing and diagnosis helps determine problems and possible causes. Its recommended you use a factory manual when performing repairs on your inboard engine, additional safety precautions, or technical data maybe included. 

SYMPTOMS: Engine Surges

CAUSES

1.0 Leaking idle air control (IAC), intake manifold or throttle body gaskets

1.1 Throttle valves worn or damaged

1.2 Worn or leaking IAC hose or vacuum hose to the pressure regulator 

ACTIONS NEEDED

1.0 Find and replace the leaking gaskets.

1.1 Inspect the throttle valves. Replace the throttle body if necessary.

1.2 Find and replace the leaking hose.

MerCruiser Low Top Speed/Lack Of Power

SYMPTOMS: Low top speed or lack of power 

CAUSES

Leaking idle air control (IAC), intake manifold or throttle body gaskets 

ACTIONS NEEDED

Find and replace the leaking gaskets. 

MerCruiser Poor cold engine operation

SYMPTOMS: Poor cold engine operation   

CAUSES

3.0 Engine is not reaching normal operating temperature

3.1 Faulty engine temperature sensor (ECT)

3.2. Fuel PSI too high or too low 

3.3 Throttle valves worn or damaged

3.4 Engine flooding 

ACTIONS NEEDED

3.0 Replace thermostat or thermostat housing gasket.

3.1 Replace the ECT.

3.2 Determine the cause and repair.

3.3 Inspect the throttle valves. Replace the throttle body if necessary.

3.4 Check the fuel pressure. If too high, find cause and correct. Clean the flame arrestor. Perform the cylinder balance test. 

MerCruiser Engine stalls

SYMPTOMS: Engine Stalls   

CAUSES

4.0 Idle rpm too low

4.1 Engine flooding

4.2 Leaking idle air control (IAC), intake manifold or throttle body gaskets 

ACTIONS NEEDED

4.0 Clean the flame arrestor. Test the IAC to see if it opens and closes properly.

4.1 Check the fuel pressure. If too high, find cause and correct. Inspect the fuel pressure regulator. Inspect the injectors.

4.2 Find and replace the leaking gaskets.

MerCruiser Engine Misses

SYMPTOMS: Engine Misses

CAUSES

Fault in the ignition system

ACTIONS NEEDED

Check the spark plugs. Check the spark plug wires. Check the distributor cap for cracks or marks. Check the ignition coil operation. Replace the faulty component. 

These service procedures apply to: 2001 2002 2003 2004 2005 2006 Mercury MerCruiser 5.0L, 5.7L, 6.2L MPI Gasoline Multiport Injection Engine.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 and 350 MAG MPI Tow Sports.