Mercury MERCRUISER, Service Manual, Page: 81 / 566

Diagnosis by Symptom
Chart S1: Engine Surges
Definition: Engine power variation under steady throttle. Feels like the engine speeds up or slows down with no change in the
throttle position.
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
• 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 4.
4
Check for proper fuel pressure while the condition exists.
Was a problem found?
Go to
Chart T3
. Go to step 5.
5
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 the spark plugs.
Were the spark plugs damaged?
Replace the spark plugs. Go to step 6.
6
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 7.
7
• Check the integrity of the primary and secondary wiring.
• Check the wire routing.
• Check the condition of the spark plug wires.
Was a problem found?
Repair or replace bad spark
plug wires.
Retest the system.
Go to step 8.
8
Check the vacuum hoses for splits, kinks, and improper
connections.
Was a problem found?
Repair or replace the
vacuum hoses.
Go to step 9.
9
Check the fuel injector wiring harness for improper connections
and intermittent opens or shorts.
Was a problem found?
Repair or replace the fuel
injector wiring harness.
Retest the system.
Go to step 10.
10
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 11.
11 Check the alternator voltage output.
Is the output 13.9–14.7 V?
Go to step 12.
Refer to
Section 4C
‑
Charging System
.
12
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 S2: Lack of Power, Sluggish, or Spongy
Definition: Engine delivers less than expected power. Little or no increase in speed when the throttle lever is advanced partially.
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.
Troubleshooting
90-8M0099748 eng DECEMBER 2015 © 2016 Mercury Marine Page 1D-11