Throughout this publication, Dangers, Warnings and Cautions (accompanied by the
International HAZARD Symbol
concerning a particular service or operation that may be hazardous if performed incorrectly
or carelessly. OBSERVE THEM CAREFULLY!
These Safety Alerts alone cannot eliminate the hazards that they signal. Strict compliance
to these special instructions when performing the service, plus common sense operation,
are major accident prevention measures.
Immediate hazards which will result in severe personal injury or death.
Hazards or unsafe practices which could result in severe personal injury or death.
Hazards or unsafe practices which could result in minor personal injury or product
or property damage.
Notice to Users of This Manual
) are used to alert the mechanic to special instructions
DANGER
WARNING
CAUTION
This service manual has been written and published by the Service Department of Mercury
Marine to aid our dealers’ mechanics and company service personnel when servicing the
products described herein.
It is assumed that these personnel are familiar with marine product servicing procedures.
Furthermore, it is assumed that they have been trained in the recommended service
procedures of Mercury MerCruiser product, including the use of mechanics’ common hand
tools and the special Mercury Marine or recommended tools from other suppliers.
We could not possibly know of and advise the marine trade of all conceivable procedures
and of the possible hazards and/or results of each method. Therefore, anyone who uses
a service procedure and/or tool, which is not recommended by the manufacturer, first must
completely satisfy himself that neither his nor the products safety will be endangered.
All information, illustrations and specifications contained in this manual are based on the
latest product information available at the time of publication. As required, revisions to this
manual will be sent to all dealers contracted by us to sell and/or service these products.
We reserve the right to make changes to this manual without prior notification.
Refer to dealer service bulletins, operation maintenance and warranty manuals and
installation manuals for other pertinent information concerning the products described in
this manual.
90-864573 FEBRUARY 2002Page i
Page 3
Precautions
It should be kept in mind, while working on the product, that the electrical system and ignition
system are capable of violent and damaging short circuits or severe electrical shocks. When
performing any work where electrical terminals could possibly be grounded or touched by
the mechanic, the battery cables should be disconnected at the battery.
Any time the intake or exhaust openings are exposed during service they should be covered
to protect against accidental entrance of foreign material which could enter the cylinders and
cause extensive internal damage when the engine is started.
It is important to note, during any maintenance procedure replacement fasteners must have
the same measurements and strength as those removed. Numbers on the heads of the
metric bolts and on the surfaces of metric nuts indicate their strength. American bolts use
radial lines for this purpose, while most American nuts do not have strength markings.
Mismatched or incorrect fasteners can result in damage or malfunction, or possibly personal
injury. Therefore, fasteners removed should be saved for reuse in the same locations
whenever possible. Where the fasteners are not satisfactory for re-use, care should be
taken to select a replacement that matches the original.
Engine Mechanical Components
Many of the engine mechanical components are designed for marine applications. Unlike
automotive engines, marine engines are subjected to extended periods of heavy load
and wide open throttle operation and, therefore, require heavy-duty components. Special
marine engine parts have design and manufacturing specifications that are required to
provide long life and dependable performance. Marine engine parts also must be able to
resist the corrosive action of salt or brackish water that will rust or corrode standard
automotive parts within a short period of time.
Failure to use recommended Quicksilver service replacement parts can result in poor
engine performance and/or durability, rapid corrosion of parts subjected to salt water and
possibly complete failure of the engine.
Replacement Parts
Electrical, ignition and fuel system components on MerCruiser Engines and
Sterndrives are designed and manufactured to comply with U.S. Coast Guard Rules
and Regulations to minimize risks of fire or explosion.
Use of replacement electrical, ignition or fuel system components, which do not
comply with these rules and regulations, could result in a fire or explosion hazard
and should be avoided.
When servicing the electrical, ignition and fuel systems, it is extremely important
that all components are properly installed and tightened. If not, any electrical or
ignition component opening would permit sparks to ignite fuel vapors from fuel
system leaks, if they existed.
Failure to use recommended Quicksilver service replacement parts can result in poor
engine performance and/or durability, rapid corrosion of parts subjected to salt water and
possibly complete failure of the engine.
Use of parts other than recommended service replacement parts will void the warranty on
thosepartswhicharedamagedasaresultoftheuseofotherthan
recommended replacement parts.
WARNING
Page ii90-864573 FEBRUARY 2002
Page 4
Models Covered in This Manual
0M30000
0andAb
Sterndrive (MCM)Serial Number
4.3L MPI Alpha and Bravo
5.0L MPI Alpha and Bravo
350 MAG MPI Alpha and Bravo
350 MAG MPI Alpha and Bravo Horizon
MX 6.2 MPI
MX 6.2 MPI Horizon
Inboard and Tow Sports (MIE)Serial Number
350 MAG MPI Inboard
350 MAG MPI Horizon Inboard
MX 6.2 MPI Inboard
MX 6.2 MPI Horizon Inboard
350 MAG MPI Tow Sports
0M310000 and Above
ove
90-864573 FEBRUARY 2002Page iii
Page 5
THIS PAGE IS INTENTIONALLY BLANK
Page iv90-864573 FEBRUARY 2002
Page 6
Service Manual Outline
Section 1 - General Information
General Information
1
Section 2 - Troubleshooting
Section 3 - Wiring Diagrams
Troubleshooting
2
Wiring Diagrams
3
5
8
90-864573 FEBRUARY 2002Page v
Page 7
SECTION 1A - GENERAL INFORMATION
How To Use This Guide1A-2..............
Abbreviations1A-3.......................
Special Tools1A-4.......................
Precautions1A-10........................
Service Precautions1A-12...............
General Specifications1A-14...............
4.3 liter (262 cid)1A-14.................
5.0 liter (305 cid)1A-14.................
5.7 liter (350 cid)1A-15.................
6.2 liter (377 cid)1A-15.................
General Information1A-16.................
Electrostatic Discharge Damage1A-16....
Wiring Harness Service1A-16............
Wiring Connector Service1A-17..........
Intermittents1A-18.....................
SECTION 2A - TROUBLESHOOTING
Troubleshooting
Without A Diagnostic Tool2A-2............
Troubleshooting
With A Diagnostic Tool2A-3..............
Troubleshooting Worksheet2A-4...........
ECM Calibration Label2A-4............
Data Collection2A-5...................
PCM 555/ECM 555
Scan Tool Worksheet2A-5.............
Preliminary Checks2A-8..................
Visual / Physical Checklist2A-8.........
On-Board Diagnostic
(OBD) System Chart2A-9.............
Fuel Pressure Gauge Setup2A-11........
Symptom Charts2A-12....................
Chart A-1 Engine Cranks Over
But Will Not Start2A-12.................
Chart A-2 Main Power Relay Test2A-13...
Chart A-3 Fuel System Electrical Test2A-14
Chart A-4 Fuel System Diagnosis2A-15...
Chart A-5 Ignition System Test2A-17.....
Chart A-6 Hard Start Symptom2A-19.....
Chart A-7 Engine Surges Symptom2A-22.
Electronic Control Module
(ECM) and Sensors1A-20.................
General Description1A-20...............
Computers and Voltage Signals1A-20....
Analog Signals1A-20...................
Digital Signals1A-22....................
Engine Control Module (ECM)1A-23......
Engine Guardian System1A-24.............
General Description1A-24...............
Warning Chart1A-25....................
General Reference Charts1A-28............
Manifold Vacuum / Pressure1A-28.......
Vacuum Gauge vs MAP Sensor1A-29....
Centigrade to Fahrenheit Conversion1A-30
Chart A-8 Lack Of Power, Sluggish
or Spongy Symptom2A-24..............
Chart A-9 Detonation /
Spark Knock Symptom2A-26...........
Chart A-10 Hesitation, Sag
or Stumble Symptom2A-29.............
Chart A-11 Cuts Out
or Misses Symptom2A-31..............
Chart A-12 Rough, Unstable or
Incorrect Idle and Stalling Symptom2A-33
Chart A-13 Poor Fuel
Economy Symptom2A-35..............
Chart A-14 Dieseling or
Run-On Symptom2A-37................
Chart A-15 Backfire Symptom2A-38......
Symptom Quick Reference Chart2A-40......
Engine Fault Quick Reference Chart2A-43...
Injector Balance Test2A-47................
Test Procedure2A-47...................
Test Example2A-49....................
Mercury MerCruiser
Scan Tool Flowchart2A-50..............
Digital Diagnostic Terminal Flowchart2A-51
Page vi90-864573 FEBRUARY 2002
Page 8
SECTION 3A - WIRING DIAGRAMS
Sensor Locations3A-2....................
Engine Harness Legend3A-4..............
Wire Splice Description3A-4............
Wire Color Code Abbreviations3A-4.....
ECM Pinout3A-5......................
ECM 555 EFI System Engine
Wiring Diagrams3A-6....................
Typical Starting System3A-6............
Wake, Horn and Tachometer Circuits3A-8
Fuses, IAC and Relays3A-9............
MAP/T, CPS and TPS3A-10.............
ECT, Seawater Pump and
Oil Pressure Sensors3A-11.............
Gear Indicator and Shift Interrupt3A-12...
Fuel Injector Control Circuits
This diagnostic guide is separated into 3 sections: General Information, Troubleshooting
and Wiring Diagrams.
General Information covers:
General wiring information
Engine Guardian description
Warning chart
Troubleshooting covers:
Basic scan tool information
Symptom trouble chart
Fault chart
Wiring diagram covers:
Engine electrical harness
Circuit diagrams
Troubleshooting covers possible electrical and mechanical causes for engine faults on the
scan tool. In wiring diagrams, the single circuit diagrams cover each sensor and subset of
the electrical system of the engine. These two sections will help the technician pinpoint
problems occurring in the electrical system.
Page 1A-290-864573 FEBRUARY 2002
Page 12
SERVICE MANUAL NUMBER 36
Abbreviations
ampAmperesin. hgInches Of Mercury
BAROBarometric PressureINJInjector
GENERAL INFORMATION
Bat
Battery Positive Terminal, Bat-
tery or System Voltage
kPaKilopascal
B+Battery Positive VoltageKSKnock Sensor System
BpsBeepskVKilovolts
CAMCamshaftmAmilliamperes
condConditionMPRMain Power Relay
contContinuousMAPManifold Air Pressure
CrankCrankshaftMATManifold Air Temperature
CANControl Area NetworkmohmsMilliohms
CKTCircuitmSecMillisecond
CMPCamshaft Position SensorN/CNormally Closed
ConnConnectorN/ONormally Open
CPSCrankshaft Position SensorOBDOn-Board Diagnostic Test
DISDistributorless Ignition SystemRFIResistance Frequency Interval
DLCData Link ConnectorROMRead Only Memory
DtcDiagnostic Trouble CodeRPMRevolutions per Minute
DMM
DMT
Digital MultimeterSWSwitch
DVOM
ECMElectronic Control ModuleTA CHTachometer
ECTEngine Coolant TemperatureTERMTerminal
EFIElectronic Fuel InjectorTPSThrottle Position Sensor
EMCT
Exhaust Manifold Coolant
Temperature
VVolts
ESTElectronic Spark TimingVA CVacuum
GNDGroundVDCVolt Direct Current
IACIdle Air ControlVOAVolt/Ohm/Amp Meter
IGNIgnitionWOTWide Open Throttle
90-864573 FEBRUARY 2002Page 1A-3
Page 13
GENERAL INFORMATIONSERVICE MANUAL NUMBER 36
Special Tools
DMT 2000A Tachometer /
Multi-Meter Kit
Description:
Measures rpm on both 2 and 4 cycle
marine engines, records the maximums
and minimums simultaneously and will
read accurately in high RFI
environments.
Replacement Components:
91-854010-1 8 ft (2.4 m) Inductive
Pick-Up
91-854011-1 Temperature Probe
91-854012 Ferrite Core
91-854013-1 Interface Module
91-854014-1 Hard Carrying Case
91-854015-1 User’s Guide
91-802651 Test Leads
Optional Accessories:
84-854016T 8 ft (2.4 m) Inductive
Pick-Up Extension
91-802650 Clamp-On Current Probe
91-89045-1 Direct Voltage Adaptor
91-854009A3
77959
DVA / Multi-Meter Kit91-99750A1
Description:
Tests the electrical and ignition systems;
consists of a VOA meter with built-in
direct voltage adaptor.
73609
Page 1A-490-864573 FEBRUARY 2002
Page 14
SERVICE MANUAL NUMBER 36
Special Tools (continued)
GENERAL INFORMATION
Digital Diagnostic Terminal
DDT
Description:
Display problem codes stored in the
ECM. It also allows the monitoring of
various circuits and components in the
fuel injection system. Must order the
91-803999 cartridge for MEFI 1, MEFI 2
and MEFI 3 ECM models 91-880118A2
cartridge for ECM 555 and PCM 555
models.
84-825003A1 Replacement 10 ft (3 m)
25-pin Harness
91-8404805 Optional Heavy Duty
Carrying case
Accessories:
An additional harness assembly may be
required when using the DDT, refer to
the following:
84-822560A5 Outboard Harness
Adaptor may be used with
91-823686A32 DDT Scan Tool for PCM
555 and ECM 555 models.
Use the Harness Adaptor 84-822560T12
For PCM 555 Models to adapt the 4-pin
Mercury MerCruiser connector to the
2-pin 84-822560A5 Outboard Harness.
90-864573 FEBRUARY 2002Page 1A-5
84-822560A5
84-822560T12
84-822560A5
84-822560T12
78069
78034
Page 15
GENERAL INFORMATIONSERVICE MANUAL NUMBER 36
Special Tools (continued)
Fuel Pressure Gauge Adaptor
Kit
Description:
Allows updating 91-16850A 2 and older
Fuel Pressure Gauge Kits. Adapts the
gauge to fit either the Mercury
MerCruiser or the GM Shrader valve.
This Adaptor Kit is included with the
Fuel Pressure Gauge Kit 91-881833A2.
Electrical, ignition and fuel system components on your Mercury MerCruiser are
designed and manufactured to comply with U.S. Coast Guard Rules and Regulations to minimize risks of fire and explosion.
Use of replacement electrical, ignition or fuel system components, which do not
comply with these rules and regulations, could result in a fire or explosion hazard
and should be avoided.
WARNING
Avoid injury or death and power package damage from an electrical shock, fire or
explosion. Always disconnect both battery cables from the battery before servicing
the power package.
WARNING
Be careful when cleaning flame arrestor and crankcase ventilation hose; gasoline
is extremely flammable and highly explosive under certain conditions. Ensure that
ignition key is OFF. Do NOT smoke or allow sources of spark or open flame in area
when cleaning flame arrestor and crankcase ventilation hose.
WARNING
Be careful when changing fuel system components; gasoline is extremely flammable and highly explosive under certain conditions. Ensure that ignition key is
OFF. DO NOT smoke or allow sources of spark or flame in the area while changing
fuel filter. Wipe up any spilled fuel immediately.
Page 1A-1090-864573 FEBRUARY 2002
Page 20
SERVICE MANUAL NUMBER 36
Precautions (continued)
Make sure no fuel leaks exist, before closing engine hatch.
Avoid gasoline fire or explosion. Improper installation of brass fittings or plugs into
fuel pump or fuel filter base can crack casting and/or cause a fuel leak.
Apply Loctite 565 Pipe Sealant with T eflon to threads of brass fitting or plug. Do
NOT USE TEFLON TAPE.
Thread brass fitting or plug into fuel pump or fuel filter base until finger-tight.
Tighten fitting or plug an additional 1-3/4 to 2-1/4 turns using a wrench. Do NOT
OVERTIGHTEN.
Install fuel line. To prevent overtightening, hold brass fitting with suitable
wrench and tighten fuel line connectors securely.
Check for fuel leaks.
GENERAL INFORMATION
WARNING
WARNING
CAUTION
Overheating from insufficient cooling water will cause engine and drive system
damage. Ensure that there is sufficient water always available at water inlet holes
during operation.
90-864573 FEBRUARY 2002Page 1A -11
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