Diagnosis By Symptom; Chart S1: Engine Surges; Chart S2: Lack Of Power, Sluggish, Or Spongy - Mercury MerCruiser Service Manual

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
1 Was the Visual/Physical Check completed?
2 Did the onboard diagnostic (OBD) system check complete?
• Check for contaminated fuel.
• Check fuel filters and the water‑separating fuel filter.
3
• Check for poor fuel quality and improper octane rating.
Was a problem found?
Check for proper fuel pressure while the condition exists.
4
Was a problem found?
Remove the spark plugs and check them for moisture, cracks,
wear, improper gap, burned electrodes, or heavy deposits.
5 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?
Check the ignition coil for cracks or carbon tracking.
6
Was a problem found?
• Check the integrity of the primary and secondary wiring.
• Check the wire routing.
7
• Check the condition of the spark plug wires.
Was a problem found?
Check the vacuum hoses for splits, kinks, and improper
8 connections.
Was a problem found?
Check the fuel injector wiring harness for improper connections
9 and intermittent opens or shorts.
Was a problem found?
Inspect the PCM harness connections and ground connections
10 for being tight, clean, and connected properly.
Was a problem found?
Check the alternator voltage output.
11
Is the output 13.9–14.7 V?
Review all of the procedures in this table. If all procedures have been completed and no problem found, inspect the
following:
12
• 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
1 Was the Visual/Physical Check completed?
2 Did the onboard diagnostic (OBD) system check complete?
90-8M0099748 eng DECEMBER 2015
Action
Action
Yes
Go to step 2.
Go to step 3.
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.
Repair or replace bad spark
plug wires.
Retest the system.
Repair or replace the
vacuum hoses.
Repair or replace the fuel
injector wiring harness.
Retest the system.
Repair.
Retest the system.
Go to step 12.
Yes
Go to step 2.
Go to step 3.
© 2016 Mercury Marine
Troubleshooting
No
Go to the Visual/Physical
Check.
Connect the CDS G3
service tool and scan for
faults.
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.
Refer to Section 4C ‑
Charging System.
No
Go to the Visual/
Physical Check.
Connect the CDS G3
service tool and scan for
faults.
Page 1D-11