Mercury MERCRUISER, Service Manual, Page: 82 / 566

Step Action Yes No
3
Is the engine in Guardian?
Verify the engine fault and
repair accordingly. Refer to the
PCM 112 Service Manual.
Go to step 4.
4
If possible compare engine performance with an engine of the
same model.
Is the engine performance similar?
No problem found. Go to step 5.
5
Check the flame arrestor for dirt, damage, or any restriction.
Was a problem found?
Clean or replace the flame
arrestor.
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
Remove the spark plugs and check them for moisture, cracks,
wear, improper gap, burned electrodes, or heavy deposits.
NOTE: If the spark plugs are fouled with gas or oil, the cause of
the fouling must be determined before replacing them.
Were the spark plugs damaged?
Replace the spark plugs. Go to step 9.
9
Check the ignition coil for cracks or carbon tracking.
Was a problem found?
Repair or replace the ignition
coil.
Retest the system.
Go to step 10.
10
Check for intermittent open or shorts in the ECT sensor, MAP
sensor, and TPS circuits.
Was a problem found?
Locate and repair the open or
short in the harness.
Go to step 11.
11
Inspect the PCM harness connections and ground connections
for being tight, clean, and connected properly.
Was a problem found?
Repair.
Retest the system.
Go to step 12.
12 Check the alternator voltage output.
Is the output 13.9–14.7 V?
Go to step 13.
Refer to
Section 4C
‑
Charging System
.
13
Check for excessive resistance on the bottom of the boat, such
as dirt or barnacles.
Was a problem found?
Clean the boat bottom.
Retest the system.
Go to step 14.
14
Check for proper propeller size and pitch for the boat
application.
Was a problem found?
Replace the propeller with one
appropriate for the application.
Go to step 15.
15
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?
For repair, refer to
Section 3
‑
Engine Mechanical
.
Go to step 16.
16
Review all of the procedures in this table. If all procedures have been completed and no problem found, inspect the
following:
• CDS G3 scan tool data
• All of the electrical connections within a suspect circuit or system
Chart S3: Detonation or Spark Knock
Definition: A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with
throttle opening.
Troubleshooting
Page 1D-12 © 2016 Mercury Marine 90-8M0099748 eng DECEMBER 2015