Chart S6: Rough, Unstable, Or Incorrect Idle And Stalling; Chart S7: Poor Fuel Economy - Mercury MerCruiser Service Manual

Troubleshooting
Step
Review all of the procedures in this table. If all procedures have been completed and no problem found, inspect the
following:
11
• 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
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?
Check the fuel injectors.
5
Was a problem found?
Check for adequate spark at all of the spark plugs.
6
Was adequate spark present?
Remove the spark plugs and check them for moisture, cracks,
wear, improper gap, burned electrodes, or heavy deposits.
7 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?
Check for the following:
• Low compression
• Vacuum leaks
• Sticking or leaking valves
• Bent push rods
8
• Worn rocker arms
• Broken valve springs
• 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:
9
• 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.
Page 1D-16
Action
Action
© 2016 Mercury Marine
Yes
Yes
Go to step 2.
Go to step 3.
Use known good fuel.
Replace the fuel filters.
Go to Chart T3.
Repair or replace the faulty
injector.
Go to step 7.
Replace the spark plugs.
For repair, refer to Section 3 ‑
Engine Mechanical.
90-8M0099748 eng DECEMBER 2015
No
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 Chart T4.
Go to step 8.
Go to step 9.