Troubleshooting Tests; Chart T1: Main Power Relay Test - Mercury MerCruiser Service Manual

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