Mercury MERCRUISER, Service Manual, Page: 86 / 566

Step Action Yes No
11
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 S6: Rough, Unstable, or Incorrect Idle and Stalling
Definition: Engine operates unevenly at idle. If severe, the engine or vessel may shake. Engine idle speed may vary. Either
condition may be severe enough to stall the engine.
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
Check the fuel injectors.
Was a problem found?
Repair or replace the faulty
injector.
Go to step 6.
6
Check for adequate spark at all of the spark plugs.
Was adequate spark present?
Go to step 7. Go to
Chart T4
.
7
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, determine
the cause of the fouling before replacing the spark plugs.
Was a problem found?
Replace the spark plugs. Go to step 8.
8
Check for the following:
• Low compression
• Vacuum leaks
• Sticking or leaking valves
• Bent push rods
• Worn rocker arms
• Broken valve springs
• 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 9.
9
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 S7: Poor Fuel Economy
Definition: Fuel economy is noticeably lower than expected. Also, economy is now lower than it was on this engine at one time.
Troubleshooting
Page 1D-16 © 2016 Mercury Marine 90-8M0099748 eng DECEMBER 2015