Mercury MERCRUISER, Service Manual, Page: 89 / 566

Step Action Yes No
10
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 11.
11
Check for intermittent opens or shorts to ground in the MAP
sensor circuit.
Was a problem found?
Locate and repair the open in
the harness.
Retest the system.
Go to step 12.
12
• Check for proper operation of the TPS.
• Check for throttle linkage sticking, binding, or wear causing
TPS voltage to be higher than normal.
Is the TPS operating improperly or is the voltage higher than
normal?
Locate and repair the problem
with the TPS or the throttle
linkage.
Retest the system.
Go to step 13.
13
Check for the following:
• Low compression
• Sticking or leaking valves
• 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 14.
14
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
Troubleshooting Tests
Chart T1: Main Power Relay Test
Step Action Yes No
1
• Turn the ignition key switch on.
• Listen for the main power relay (MPR).
• Turn the ignition key switch off.
With the initial ignition key on, did the MPR turn on (you should hear a
click)?
No problem found. Go to step 2.
2
• Remove the MPR.
• Turn the ignition key switch on.
• Using the DMT connected to ground, check for battery voltage (B+) at
the MPR harness connector terminal 30 and 86.
• Turn the ignition key switch off.
With the ignition key on, was B+ present?
Go to step 3.
Locate and repair the
open or short in the
harness.
Retest system.
3
Check for continuity between the MPR harness connector terminal 85 and
the PCM harness connector pin A‑3D.
Was continuity present?
Install a known
good MPR onto
the engine.
Retest system.
Locate and repair the
open in the harness.
Retest system.
Troubleshooting
90-8M0099748 eng DECEMBER 2015 © 2016 Mercury Marine Page 1D-19