Chart S3: Detonation Or Spark Knock - Mercury MerCruiser Service Manual

Troubleshooting
Step
3
Is the engine in Guardian?
If possible compare engine performance with an engine of the
4 same model.
Is the engine performance similar?
Check the flame arrestor for dirt, damage, or any restriction.
5
Was a problem found?
• Check for contaminated fuel.
• Check fuel filters and the water‑separating fuel filter.
6
• Check for poor fuel quality and improper octane rating.
Was a problem found?
Check for proper fuel pressure while the condition exists.
7
Was a problem found?
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
8
the fouling must be determined before replacing them.
Were the spark plugs damaged?
Check the ignition coil for cracks or carbon tracking.
9
Was a problem found?
Check for intermittent open or shorts in the ECT sensor, MAP
10 sensor, and TPS circuits.
Was a problem found?
Inspect the PCM harness connections and ground connections
11 for being tight, clean, and connected properly.
Was a problem found?
Check the alternator voltage output.
12
Is the output 13.9–14.7 V?
Check for excessive resistance on the bottom of the boat, such
13 as dirt or barnacles.
Was a problem found?
Check for proper propeller size and pitch for the boat
14 application.
Was a problem found?
Check for the following:
• Low compression
• Leaking cylinder head gaskets
15
• Worn camshaft
• Improper valve timing or valve train problem
• Restricted exhaust system
Was a problem found?
Review all of the procedures in this table. If all procedures have been completed and no problem found, inspect the
following:
16
• 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.
Page 1D-12
Action
© 2016 Mercury Marine
Yes
Verify the engine fault and
repair accordingly. Refer to the
PCM 112 Service Manual.
No problem found.
Clean or replace the flame
arrestor.
Use known good fuel.
Replace the fuel filters.
Go to Chart T3.
Replace the spark plugs.
Repair or replace the ignition
coil.
Retest the system.
Locate and repair the open or
short in the harness.
Repair.
Retest the system.
Go to step 13.
Clean the boat bottom.
Retest the system.
Replace the propeller with one
appropriate for the application.
For repair, refer to Section 3 ‑
Engine Mechanical.
90-8M0099748 eng DECEMBER 2015
No
Go to step 4.
Go to step 5.
Go to step 6.
Go to step 7.
Go to step 8.
Go to step 9.
Go to step 10.
Go to step 11.
Go to step 12.
Refer to Section 4C ‑
Charging System.
Go to step 14.
Go to step 15.
Go to step 16.