Mercury MERCRUISER, Service Manual, Page: 83 / 566

Step Action Yes No
1 Was the
Visual/Physical Check
completed? Go to step 2.
Go to the
Visual/Physical
Check
.
2 Did the onboard diagnostic (OBD) system check complete? Go to step 3.
Connect the CDS G3
service tool and scan for
faults.
3
Is the engine propped to operate in the recommended
operating RPM range?
Go to step 4.
Check propping
procedures.
4
Check the spark plugs for:
• Proper type (refer to
Section 1C
‑
Maintenance
)
• Proper gap (refer to
Section 1C
‑
Maintenance
)
• Damage
Was a problem found?
Replace the problem spark
plugs with those specified for
the application.
Go to step 5.
5
Check the spark plug wires for continuity or damage.
Was a problem found?
Replace the questionable
spark plug wire.
Retest the system.
Go to step 6.
6
• Check for contaminated fuel.
• Check fuel filters and the water‑separating fuel filter.
• Check for poor fuel quality and improper octane rating.
Was a problem found?
Use known good fuel.
Replace the fuel filters.
Go to step 7.
7
Check for proper fuel pressure while the condition exists.
Was a problem found?
Go to
Chart T3
. Go to step 8.
8
Is the engine operating above the normal temperature
range?
Go to step 9. Go to step 10.
9
Check for obvious overheating issues:
• Loose serpentine belt
• Faulty or incorrect seawater pump
• Restriction in the cooling system
• Faulty or incorrect thermostat
Was a problem found?
Repair or replace.
Retest the system.
Go to step 10.
10
Is a scan tool being used?
Go to step 12. Go to step 11.
11
Check for an ECT sensor shifted in value.
With the engine completely cool, measure the resistance of the
ECT sensor.
Refer to
PCM 112–Section 3A
‑
Component testing Sensor
.
Compare the approximate temperature of the ECT sensor to an
accurate reading of ambient air temperature.
Are the readings similar?
Go to step 13.
Replace the ECT sensor.
Retest the system.
12
Check for an ECT sensor shifted in value.
Using the scan tool with the engine completely cool, compare
the ECT sensor temperature with an accurate reading of
ambient air temperature.
Are the temperatures within 5.5° C (10° F) of each other?
Go to step 13.
Replace the ECT sensor.
Retest the system.
13 Check for loose fasteners, sensors, and connections. Tighten and secure. Go to step 14.
14
Check for the following:
• Low compression
• Leaking cylinder head gaskets
• Worn camshaft
• Improper valve timing or valve train problem
• Restricted exhaust system
Was a problem found?
Engine mechanical problem,
refer to
Section 3
‑
Engine
Mechanical
.
Go to step 15.
Troubleshooting
90-8M0099748 eng DECEMBER 2015 © 2016 Mercury Marine Page 1D-13