Mercury MERCRUISER, Service Manual, Page: 85 / 566

Step Action Yes No
12
Check for the following:
• Low compression
• Deposits on the intake valves
Was a problem found?
For repair, refer to
Section 3
‑
Engine Mechanical
.
Go to step 13.
13
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 S5: Engine Misses
Definition: Steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases. The
exhaust has a steady spitting sound at idle, low speed, or on hard acceleration. Fuel starvation can cause the engine to miss.
IMPORTANT: For additional information on diagnosing engine misfires, refer to the
PCM 112 Service Manual
.
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 8. 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, the cause of the
fouling must be determined before replacing the spark plugs.
Was a problem found?
Replace the spark plugs. Go to step 8.
8
Check for electromagnetic interference (EMI). A missing condition
can be caused by EMI on the reference circuit. EMI can usually be
detected by monitoring engine RPM with a scan tool or
tachometer. A sudden increase in RPM with little change in actual
engine RPM indicates EMI is present.
Was a problem found?
Locate and correct the EMI
source.
Retest the system.
Go to step 9.
9
Check for the following:
• Low compression
• 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 10.
10 Check the intake and exhaust manifolds for casting flash.
Was a problem found?
Repair or replace.
Retest the system.
Go to step 11.
Troubleshooting
90-8M0099748 eng DECEMBER 2015 © 2016 Mercury Marine Page 1D-15