MERCURY MERCRUISER 496 MAG DIAGNOSTICS Service Repair Manual SN:0M000000 and Above

Number 33
Printed in U.S.A. 90-863757--1
DECEMBER 2001
2001, Mercury Marine
PCM 555 DIAGNOSTICS
SN 0M000000 and ABOVE
SERVICE
MANUAL

90-863757--1 DECEMBER 2001 Page i
Notice
Throughout this publication, Dangers, Warnings and Cautions (accompanied by the
International HAZARD Symbol ) are used to alert the mechanic to special instructions
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.
DANGER
Immediate hazards which will result in severe personal injury or death.
WARNING
Hazards or unsafe practices which could result in severe personal injury or death.
CAUTION
Hazards or unsafe practices which could result in minor personal injury or product
or property damage.
Notice to Users of This Manual
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.

Page ii 90-863757--1 DECEMBER 2001
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 accidentalentrance of foreign materialwhich 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
WARNING
Electrical, ignition and fuel system components on MerCruiser Engines and
Sterndrives are designedand manufacturedto comply with U.S. Coast GuardRules
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
those parts which are damaged as a result of the use of other than
recommended replacement parts.

90-863757--1 DECEMBER 2001 Page iii
Models Covered in This Manual
Sterndrive (MCM) Model Serial Number
496 MAG HO 0M000000 and Above
496 MAG 0M000000 and Above
Inboard (MIE) Model Serial Number
8.1S HO 0M000000 and Above
8.1S Horizon 0M000000 and Above

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THIS PAGE IS INTENTIONALLY BLANK

1
2
3
5
8
General Information
Troubleshooting
Wiring Diagrams
90-863757--1 DECEMBER 2001 Page v
Service Manual Outline
Section 1 - General Information
Section 2 - Troubleshooting
Section 3 - Wiring Diagrams

Page vi 90-863757--1 DECEMBER 2001
SECTION 1A - GENERAL INFORMATION
Abbreviations 1A-2. . . . . . . . . . . . . . . . . . . . . . .
Special Tools 1A-3. . . . . . . . . . . . . . . . . . . . . . .
Service Precautions 1A-7. . . . . . . . . . . . . . . . .
How To Use This Guide 1A-9. . . . . . . . . . . . . .
General Information 1A-10. . . . . . . . . . . . . . . . .
Electrostatic Discharge Damage 1A-10. . . .
Wiring Harness Service 1A-10. . . . . . . . . . . .
Wiring Connector Service 1A-11. . . . . . . . . .
Intermittents 1A-11. . . . . . . . . . . . . . . . . . . . .
Ignition System 1A-13. . . . . . . . . . . . . . . . . . .
PCM 555 Engine Guardian 1A-13. . . . . . . . .
Warning System 1A-14. . . . . . . . . . . . . . . . . .
Reference Charts 1A-16. . . . . . . . . . . . . . . . .
SECTION 2A - TROUBLESHOOTING
Troubleshooting Without A Diagnostic Tool 2A-2
Troubleshooting With A Diagnostic Tool 2A-2
Troubleshooting Worksheet 2A-3. . . . . . . . . . .
PCM Calibration Label For
8.1 liter (496 cid) Engines 2A-3. . . . . . . . .
Data Collection 2A-3. . . . . . . . . . . . . . . . . . .
PCM 555/ECM 555 DDT/Rinda
8.1 liter (496 cid)/GM EFI
SCAN TOOL SHEET 2A-4. . . . . . . . . . . . .
Troubleshooting Guides 2A-7. . . . . . . . . . . . . .
Symptom Chart 2A-7. . . . . . . . . . . . . . . . . .
Fault Chart 2A-9. . . . . . . . . . . . . . . . . . . . . . .
Engine Will Not Crank Over 2A-13. . . . . . . .
Mercury MerCruiser Scan Tool
Flowchart 2A-16. . . . . . . . . . . . . . . . . . . . . . .
Digital Diagnostic Terminal Flowchart 2A-17
SECTION 3A - WIRING DIAGRAMS
Sensor Locations On The
8.1 liter (496 cid) Engine 3A-2. . . . . . . . . . . . .
8.1 Liter (496 cid) Engine Harness
Legend 3A-4. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Wire Splice Description 3A-4. . . . . . . . . . . .
PCM 555 Pinout 3A-5. . . . . . . . . . . . . . . . . .
8.1 liter (496 cid) Electrical Wiring
Diagrams 3A-8. . . . . . . . . . . . . . . . . . . . . . . . . .
Typical Starting System Components 3A-8
Positive Current Flow 3A-9. . . . . . . . . . . . .
Single Circuit Diagrams 3A-16. . . . . . . . . . . .
Wiring Diagrams 3A-38. . . . . . . . . . . . . . . . . . . .

90-863757--1 DECEMBER 2001 Page vii

Page viii 90-863757--1 DECEMBER 2001

1
A
GENERAL INFORMATIONSERVICE MANUAL NUMBER 33
90-863757--1 DECEMBER 2001 Page 1A-1
SECTION 1A - GENERAL INFORMATION
Table of Contents
Abbreviations 1A-2. . . . . . . . . . . . . . . . . . . . . . .
Special Tools 1A-3. . . . . . . . . . . . . . . . . . . . . . .
Service Precautions 1A-7. . . . . . . . . . . . . . . . .
How To Use This Guide 1A-9. . . . . . . . . . . . . .
General Information 1A-10. . . . . . . . . . . . . . . . .
Electrostatic Discharge Damage 1A-10. . . .
Wiring Harness Service 1A-10. . . . . . . . . . . .
Wiring Connector Service 1A-11. . . . . . . . . .
Intermittents 1A-11. . . . . . . . . . . . . . . . . . . . .
Ignition System 1A-13. . . . . . . . . . . . . . . . . . .
PCM 555 Engine Guardian 1A-13. . . . . . . . .
Warning System 1A-14. . . . . . . . . . . . . . . . . .
Reference Charts 1A-16. . . . . . . . . . . . . . . . .
INDEX
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GENERAL INFORMATION SERVICE MANUAL NUMBER 33
Page 1A-2 90-863757--1 DECEMBER 2001
Abbreviations
amp Amperes IAC Idle Air Control
BARO Barometric Pressure IGN Ignition
Bat
Battery Positive Terminal, Bat-
tery or System Voltage
in. hg Inches Of Mercury
B+ Battery Positive INJ Injection
Bps Beeps kPa Kilopascal
CAM Camshaft KS Knock Sensor System
cond Condition kV Kilovolts
cont Continuous mA milliamperes
Crank Crankshaft MPR Main Power Relay
CAN Control Area Network MAP Manifold Air Pressure
CKT Circuit MAT Manifold Air Temperature
CMP Camshaft Position Sensor mohms Milliohms
Conn Connector mSec Millisecond
CPS Crankshaft Position Sensor N/C Normally Closed
Cyl Cylinder N/O Normally Open
DDT Digital Diagnostic Terminal PCM Propulsion Control Module
Deg Degrees RAM Random Access Memory
Diag Diagnostic REF HI Reference High
DIS Distributorless Ignition System REF LO Reference Low
DLC Data Link Connector ROM Read Only Memory
Dtc Diagnostic Trouble Code SW Switch
DMM
DMT
DMT
DMT
Digital Multimeter TACH Tachometer
ECM Engine Control Module TERM Terminal
ECT Engine Coolant Temperature TPS Throttle Position Sensor
EFI Electronic Fuel Injector V Volts
EMCT
Exhaust Manifold Coolant
Temperature
VAC Vacuum
ENG Engine WOT Wide Open Throttle
GND Ground
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90-863757--1 DECEMBER 2001 Page 1A-3
Special Tools
DMT 2000A Tachometer /
Multi-Meter Kit
91-854009A3
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
77959
DVA / Multi-Meter Kit 91-99750A1
Description: Tests the electrical and
ignition systems; consists of a VOA
meter with built-in direct voltage adaptor.
73609
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Page 1A-4 90-863757--1 DECEMBER 2001
Digital Diagnostic Terminal
DDT
91-823686A2
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:
91-822560A13 Harness Assembly /
Diagnostic Tester
91-861540A1 Adaptor Harness
91-822560A7 Outboard Adapter
Harness
91-84-822560A5 EFI Outboard Adaptor
91-822560T12 Scan Tool Harness
Adaptor
91-822560A2 Harness Assembly /
Diagnostic Tester
74214
EFI Outboard Harness
Adaptor
Scan Tool Harness Adaptor
84-822560A5
84-822560T12
Description:
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.
84-822560A5
84-822560T12 78034
78069
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90-863757--1 DECEMBER 2001 Page 1A-5
Fuel Pressure Gauge Adaptor
Kit
91-803135
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.
Fuel Pressure Gauge Kit 91-881833A2
Description:
Use to test the fuel pump pressure,
includes:
91-803135 Fuel Pressure Gauge
Adaptor Kit
91-806901 Fuel Pressure Tee
91-881833A1 160 psi Gauge 73814
Fuel Shut Off Tool 91-805918A1
Description:
Use in fuel system pressure tests.
74227
Harness Assembly /
Diagnostic Tester
91-822560A13
Description:
25-pin to 4-pin Adaptor harness. For
PCM 555 and ECM 555 models (4-pin
connectors, no additional harness
required).
74214
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Page 1A-6 90-863757--1 DECEMBER 2001
Mercury MerCruiser DDT
Cartridge Version 1.2
91-880118A2
Description:
Use on PCM 555 and ECM 555 models.
78036
Portable Timing Light 91-99379
Description:
Checks the ignition timing, powered by
two D-cell batteries.
73664
Scan Tool Kit / Version 4.0 Note in Description
Description:
Hand-held Scan Tool updated for 2001.
(refer to Service Bulletin 2001-1). Use
with models:
MCM/MIE EFI (TBI) and MPI Gasoline
MCM/MIE 496/8.1S MPI PCM 555
1997 and Newer MCM/MIE Carburetor
Models with Thunderbolt Ignition System
MCM/MIE D-Tronic Diesel
NOTE: Tool must be ordered from Rinda
Technologies, Inc.
72428
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90-863757--1 DECEMBER 2001 Page 1A-7
Special Tools (continued)
NOTE: 1The High Impedance Multimeter that comes with the existing Outboard 2 Cycle EFI
Tester, P/N 91-11001A2 meets the requirements listed above.
NOTE: 2Quicksilver DigitalTachometer / Multi-Meter (DMT 2000) P/N91-854009A1, meets
the requirements listed above.
NOTE: 3 Using a test light with 100 mA or less rating may show a faint glow when test
actually states no light.
Tools may be ordered from:
Kent-Moore
Tools, Inc.
Rinda
Technologies
Mercury Marine OTC
29784 Little Mack 4563 N. Elston Ave. W6250 Pioneer Road,
P.O. Box1929
28635 Mound Rd.
Roseville, MI
48066
Chicago, IL 60630 Fond Du Lac, WI 54936-1939 Warren, MI 48092-3499
Phone:
800-345-2233
Phone:
773-736-6633
Phone: 920-929-5589,
800-487-MERC
Phone: 586-574-2332,
800-328-6657
Fax: 773-736-2950 Fax: 920-457-8736
E-mail:
Sales@rinda.com
www.MERCURYMARINE.com www.servicesolutions.spx.com
Service Precautions
Observe the following:
 Before removing any ECM system component, disconnect both battery cables.
 Never start the engine without the battery being solidly connected.
 Never separate the battery from the on-board electrical system while the engine is
operating.
 Never disconnect battery cables from the charging system while the engine is
operating.
 When charging the battery, disconnect it from the boat’s electrical system.
 Ensure that all cable harnesses are connected and that battery connections are
clean.
 Never connect or disconnect the wiring harness at the ECM when the ignition is
switch is in the on position.
 Before attempting any electric arc welding, disconnect the battery leads and the
ECM connectors.
 When steam cleaning engines, do not direct the steam cleaning nozzle at ECM
system components. If this happens, corrosion of the terminals or damage of
components can occur.
 Use only the test equipment specified in the diagnostic charts, since other test
equipment may either give incorrect results or damage good components.
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Page 1A-8 90-863757--1 DECEMBER 2001
 All voltage measurements using a voltmeter require a digital voltmeter with a rating
of 10 megaohms input impedance.
 When a test light is specified, a low-power test light must be used. Do NOT use a
high-wattage test light. While a particular brand of test light is not suggested, a
simple test, as shown below, on any test light will ensure it to be safe for system
circuit testing. Connect an accurate ammeter (such as the DMT) in series with the
test light being tested and power the test light ammeter circuit with the battery.
b
a
c
a - Test Light
b - Battery
c - Ammeter
IMPORTANT: If the ammeter indicates LESS than 3/10 amp current flow (.3 A or 300
mA), the test light is SAFE to use. If the ammeter indicates MORE than 3/10 amp
current flow (.3 A or 300 mA), the test light is NOT SAFE to use.
NOTE: Using a test light with 100 mA or less rating may show a faint glow when test actually
states no light.
 When using a DMT to perform voltage measurements, switch to the OFF position
when connecting the DMT to the circuitry being tested.
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How To Use This Guide
This diagnostic guide is separated into 3 sections: General Information, Troubleshooting
and Wiring Diagrams.
General Information covers:
 General wiring information
 General distributorless ignition system (DIS) description
 Engine Guardian description
 Warning chart
Troubleshooting covers:
 Basic scan tool information
 Symptom trouble chart
 Fault chart
Wiring diagram covers:
 Engine EFI harness
 10-pin harness
 Single circuit diagrams
Troubleshooting gives 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 8.1 liter/496 cid engine. These two sections will help the
technician pinpoint problems occurring in the electrical system.
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Page 1A-10 90-863757--1 DECEMBER 2001
General Information
Electrostatic Discharge Damage
Electronic components are often designed to carry very low voltage and are susceptible
to damage caused by electrostatic discharge. It is possible for less than 100 volts of
static electricity to cause damage to some electronic components. By comparison, it takes
4,000 volts for a person to even feel the effect of a static discharge.
There are several ways for a person to become statically charged. The most common
methods are by friction and by induction. An example of charging by friction is a person
sliding across a seat, in which a charge of as much as 25,000 volts can build up. Charging
by induction occurs when a person with well-insulated shoes stands near a highly charged
object and momentarily grounds the circuit. Charges of the same polarity are drained off,
leaving the person highly charged with the opposite polarity. Static charges of either type
can cause damage electronic components. Use care when handling and testing electronic
components.
Wiring Harness Service
Marine engine control circuits contain many special design features not found in standard
land vehicle wiring. Environmental protection is used extensively to protect electrical
contacts and proper splicing methods must be used.
IMPORTANT: Before component replacement and/or during normal troubleshooting
procedures, visually inspect any questionable mating connector.
The proper operation of low amperage input/output circuits depends upon good continuity
between circuit connectors. Mating surfaces should be properly formed, clean and likely to
make proper contact. Some typical causes of connector problems are listed below.
1. Improperly formed contacts and/or connector housing.
 Damaged contacts or housing due to improper connection.
 Corrosion, sealer or other contaminants on the contact mating surfaces.
2. Incomplete mating of the connector halves during initial assembly or during subsequent
troubleshooting procedures.
3. Tendency for connectors to come apart due to vibration and/or temperature cycling.
4. Terminals not fully seated in the connector body.
5. Inadequate terminal crimps to the wire.
Wire harnesses should be replaced with the appropriate replacement part, refer to specified
part numbers. When signal wires are spliced into a harness, only use high temp insulated
wire the same gauge as the existing harness.
With the low current and voltage levels found in the system, it is important to solder splices
and create the best possible connection, refer to Wire Repair.
Use care when probing a connector or replacing connector terminals. It is possible to short
between opposite terminals. If this happens, certain components can be damaged. Always
use jumper wires with the corresponding mating terminals between connectors for circuit
checking. NEVER probe through connector seals, wire insulation, secondary ignition wires,
boots or covers. Microscopic damage or holes will result in eventual water intrusion,
corrosion and/or component or circuit failure.
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90-863757--1 DECEMBER 2001 Page 1A-11
WIRE REPAIR
1. Locate damaged wire.
2. Remove insulation as required.
73048
3. Splice two wires together using splice clips and rosin core solder.
73048
4. Cover splice with heat shrink sleeve to insulate from other wires.
73048
Wiring Connector Service
Most connectors in the engine compartment are protected against moisture and dirt that
could create oxidation and deposits on the terminals. This protection is important because
of the very low voltage and current levels found in the electronic system. The connectors
have a lock that secures the male and female terminals together. A secondary lock holds
the seal and terminal into the connector.
When diagnosing, open circuits are often difficult to locate by sight because oxidation or
terminal misalignment are hidden by the connectors. Merely wiggling a connector on a
sensor or in the wiring harness may locate the open circuit condition. This should always
be considered when an open circuit or failed sensor is indicated. Intermittent problems may
also be caused by oxidized or loose connections.
Before making a connector repair, be certain of the type of connector. Some connectors look
similar but are serviced differently. Replacement connectors and terminals are listed in the
Mercury Precision Parts / Quicksilver Accessories Guide.
Ensure that the connector seals are not deformed or crushed when mating the connectors
together.
Intermittents
IMPORTANT: Intermittent problems may or may not store a fault. The fault must be
present to locate the problem.
Most intermittent problems are caused by faulty electrical connections or wiring. Perform
a careful visual check for the following conditions:
 Poor mating of the connector halves, or a terminal not fully seated in the connector
body.
 Improperly formed or damaged terminals and/or connectors.
All connector terminals in the problem circuit should be carefully checked for proper contact
tension.
 Poor terminal-to-wire connection (crimping). Remove the terminal from the connector
body to check.
The vessel may be driven with a Digital Multimeter connected to a suspected circuit. An
abnormal voltage when malfunction occurs is a good indication that there is a fault in the
circuit being monitored.
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Page 1A-12 90-863757--1 DECEMBER 2001
A diagnostic tool can be used to help detect intermittent conditions. The diagnostic tool
allows manipulation of wiring harnesses or components with the engine not operating, while
observing the scan tool readout. The diagnostic tool can also be plugged in and observed
while operating the vessel.
If the problem seems to be related to certain parameters that can be checked on the scan
tool, they should be checked while operating the vessel. If there does not seem to be any
correlation between the problem and a specific circuit use the diagnostic tool data to see
if there is any change in the readings that might indicate intermittent operation.
The diagnostic tool is also an easy way to compare the operating parameters of a poorly
operating engine with those of a known good one. For example, a sensor may shift in value
but not set a fault. Comparing the sensor’s readings with those of the typical scan tool data
readings may uncover the problem.
The diagnostic tool has the ability to save time in diagnosis and prevent the replacement
of good parts. The key to using the diagnostic tool successfully lies in the technician’s ability
to understand the system being diagnosed and the diagnostic tool operation and limitations.
The technician should read the tool manufacturer’s operating manual to become familiar
with the tool’s operation.
To check loss of fault memory, disconnect TP sensor and idle engine. Attach diagnostic tool.
The fault TPS1 CKT Lo should be stored and kept in memory when ignition is turned OFF.
If not, the ECM is faulty. When this test is completed clear the fault.
An intermittent may be caused by the following:
 Ignition coil shorted to ground and arcing at ignition wires or plugs.
 Poor ECM grounds.
 An electrical system interference caused by a sharp electrical surge. Normally, the
problem will occur when the faulty component is operated.
 Improper installation of electrical options such as lights, ship to shore radios and
sonar.
 Knock sensor wires are routed too close to spark plug wires, ignition system
components or charging system components.
 Secondary ignition components shorted to ground or an open ignition coil ground
(coil mounting brackets).
 Components internally shorted to ground such as starters, alternators or relays.
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90-863757--1 DECEMBER 2001 Page 1A-13
Ignition System
WARNING
High voltage produced by the ignition system can cause personal injury or property
damage. Disconnect both battery cables, before working on the ignition system
and use caution while troubleshooting the ignition system.
The distributorless ignition system (DIS) is designed to replace the mechanical distributor
system in controlling the ignition secondary voltage. It has no moving parts and does not
require timing adjustments. All ignition coils are designed to operate with the secondary
loaded. However, this is particularly true with DIS.
Coil design saturation time and primary current flow on distributorless systems are modified
to produce more available energy. If maximum current is attained, the dwell time is
shortened to reduce the wattage consumed by the system. If minimum current is not
attained, dwell time is increased to allow full saturation of the ignition coil. If current limiting
occurs prior to discharge, dwell is decreased for the next sequence.
A sensing device is used to determine the crankshaft and camshaft position. Hall Effect
sensors are used on the 8.1 liter/496 cid engine to synchronize and fire the coils at the
proper time. A Hall Effect sensor has a magnetic field introduced perpendicular to a current
flowing through a solid conductor causing a measurable voltage. This is why the voltage
readings on these two sensors fluctuate within a range, generating a square wave with the
same pattern as on the interrupter vanes on the sensor. Full voltage will be present when
there is no vane on the sensor.
The crankshaft sensor is placed near a machined wheel on the crankshaft. As the crank
rotates, the camshaft sprocket also rotates at one-half engine speed. The camshaft signal
is synchronized with one of the crankshaft signal pull downs. The PCM processes the
voltage signal from the sensor to determine engine position and engine speed. After 1-1/2
to 2 revolutions, the PCM will sync the camshaft and crankshaft sensors and charge the
secondary circuit of the coil.
PCM 555 Engine Guardian
Engine Guardian is the focalpoint of the self-diagnostic strategy of PCM 555. It helps protect
the engine from possible damage that could result from several faulty conditions. The
system monitors the sensors incorporated on the engine and if a malfunction is discovered,
a fault description is stored in the PCM and available power is normally reduced. By
ensuring that engine output is at a low enough level, the engine is better protected from
thermally induced failures.
For example, if an open or short is found in an exhaust manifold sensor, available power
will be reduced to 90% of total, the audio alarm will sound 2 beeps per minute (2 Bp/min)
and the MercMonitor gauge (SC1000) will display a warning lamp. In an exhaust manifold
overheat condition, the maximum rpm will vary with the temperature of the manifold and
could be limited to idle in extreme cases of overheating, a constant beep will sound and the
SC1000 will display a warning lamp.
IMPORTANT: Engine Guardian cannot guarantee that engine damage will not occur
when adverse operating conditions are encountered. Engine Guardian is designed
to warn the operator of an adverse condition and to reduce power by limiting rpm in
an attempt to reduce possible engine damage. The boat operator is ultimately
responsible for proper engine operation.
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Page 1A-14 90-863757--1 DECEMBER 2001
Warning System
The engine warning system incorporates an audio alarm and, if installed, a SC1000 System
Monitor. When the key switch is turned to the ON position, the audio alarm will momentarily
activate to test the warning system. The alarm should sound once if the system is operable.
This table is a guick guide, showing what warning output will accompany a fault.
Fault SC1000
Audio
Alarm
Available
Power
Description
Cam Sensor Yes 2 Bp/min 90%
Open or short, engine
must be cranking to set
this fault code.
ECT CKT HI Yes 2 Bp/min 90% Open
ECT CKT LO Yes 2 Bp/min 90% Short
ECT Coolant
Overheat
Yes Constant 6-100 %
Engine guardian overheat
condition
EST 1-8 Open Yes 2 Bp/min NA Coil harness wire open
EST 1-8 Short Yes 2 Bp/min NA Coil harness wire short
Fuel Injector 1-8
Open
Yes 2 Bp/min NA Fuel injector wire open
Fuel Injector 1-8
Short
Yes 2 Bp/min NA Fuel injector wire short
IAC Output Yes 2 Bp/min 90% Only with rpm
Knock Sensor 1 Yes 2 Bp/min 90%
Alarm sounds for 20
seconds in NEUTRAL and
indefinitely in gear.
Knock Sensor 2 Yes 2 Bp/min 90%
Alarm sounds for 20
seconds in NEUTRAL and
indefinitely in gear.
Low Drive Lube
Strategy
Yes Steady Bp 0-100% Low oil in sterndrive
Low Oil Pressure
Strategy
Yes Constant 0-100% Low oil pressure strategy
MAP Sensor 1 Input
High
No 2 Bp/min 90%
Short, no visual on
SC1000
MAP Sensor 1 Input
Low
No 2 Bp/min 90%
Open, no visual on
SC1000
MAT Sensor Yes 2 Bp/min 90%
Open or short in MAT
circuit
NOTE: If any 5v sensor becomes shorted to ground the engine will not start. If the engine
is operating when the short occurs the engine may stop operating and will not start.
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90-863757--1 DECEMBER 2001 Page 1A-15
Fault SC1000
Audio
Alarm
Available
Power
Description
Oil PSI CKT Hi Yes 2 Bp/min 90% Short, defaults to 51.7 psi
Oil PSI CKT Lo Yes 2 Bp/min 90% Open, zero oil pressure
Overspeed Yes Constant RPM Limit Engine over rpm limit
Port EMCT CKT Hi Yes 2 Bp/min 90%
Open, defaults to 32
degrees F (0 degree C)
Port EMCT CKT Lo Yes 2 Bp/min 90%
Short, defaults to 32
degrees F (0 degree C)
Port EMCT CKT
Overheat
Yes Constant 6-100%
Overheat condition, 212
degrees F (100 degrees C)
limit
Sea Pump PSI Lo Yes Constant 6-100%
Low water pressure
strategy, defaults to
43.4 psi
Sea Pump CKT Hi Yes 2 Bp/min 90% Open
Sea Pump CKT Lo Yes 2 Bp/min 90% Short
STB EMCT CKT Hi Yes 2 Bp/min 90%
Open, defaults to 32
STB EMCT CKT Lo Yes 2 Bp/min 90%
Short, defaults to 32
STB EMCT CKT
Overheat
Yes Constant 6-100%
Overheat condition, 212
degrees (100 degrees C)
limit
Steer CKT Hi Yes No No Open and short
TPS1 CKT Hi Yes 2 Bp/min 90%
Short, signal to 5v+,
engine will not start. Refer
to data monitor screen.
TPS1 CKT Lo Yes 2 Bp/min 90% Open
TPS 1 Range Hi Yes 2 Bp/min 90% Above 4.8v, 994 counts
TPS 1 Range Lo Yes 2 Bp/min 90% Below 0.5v, 35 counts
Trim CKT Hi Yes No No
Short, high range, visual
warning on SC1000 only.
Trim CKT Lo Yes No No
Open, low range, visual
warning on SC1000 only.
5 VDC PWR Low Yes 2 Bp/min varies Short any 5v+ to ground
NOTE: If any 5v sensor becomes shorted to ground the engine will not start. If the engine
is operating when the short occurs the engine may stop operating and will not start.
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Page 1A-16 90-863757--1 DECEMBER 2001
Reference Charts
8.1 LITER/496 CID RESISTANCE READINGS AT 70 DEGREES F (21 DEGREES C)
Sensor Pinout Value
SEA PUMP, OIL, PITOT
PRESSURE
A-B 31.5 kohms
PRESSURE A-C 42.9 kohms
MAT A-B 3.14 ohms
ECT A-B 3.12 kohms
EMCT A-B 11.01 kohms
MAP A-B 9.33 kohms
A-C 3.89 ohms
B-C 5.44 kohms
CAMSHAFT SENSOR A-B 24.04 mohms
B-C 24.5 mohms
CRANKSHAFT SENSOR A-B 23.30 mohms
B-C 23.21 mohms
IAC 1-2 10.1 ohms
FUEL INJECTOR A-B 12 ohms
TRIM SENDER
A B 0 614 mohms
set to index mark
A-B 0.614 mohms
All values have a range of +/-- 2 percent.
COVER

90-863757--1 DECEMBER 2001 Page 1A-17
MANIFOLD VACUUM / PRESSURE
Manifold
Vacuum Absolute Pressure
Manifold
Vacuum Absolute Pressure
psi psi kPa psi psi kPa
0 14.7 101.3 7 1/4 7.45 51.4
1/4 14.45 99.6 7 1/2 7.2 49.6
1/2 14.2 97.9 7 3/4 6.95 47.9
3/4 13.95 96.2 8 6.7 46.2
1 13.7 94.4 8 1/4 6.45 44.5
1 1/4 13.45 92.7 8 1/2 6.2 42.7
1 1/2 13.2 91.0 8 3/4 5.95 41.0
1 3/4 12.95 89.3 9 5.7 39.3
2 12.7 87.5 9 1/4 5.45 37.6
2 1/4 12.45 85.8 9 1/2 5.2 35.8
2 1/2 12.2 84.1 9 3/4 4.95 34.1
2 3/4 11.95 82.4 10 4.7 32.4
3 11.7 80.6 10 1/4 4.45 30.7
3 1/4 11.45 78.9 10 1/2 4.2 29.0
3 1/2 11.2 77.2 10 3/4 3.95 27.2
3 3/4 10.95 75.5 11 3.7 25.5
4 10.7 73.8 11 1/4 3.45 23.8
4 1/4 10.45 72.0 11 1/2 3.2 22.1
4 1/2 10.2 70.3 11 3/4 2.95 20.3
4 3/4 9.95 68.6 12 2.7 18.6
5 9.7 66.9 12 1/4 2.45 16.9
5 1/4 9.45 65.1 12 1/2 2.2 15.2
5 1/2 9.2 63.4 12 3/4 1.95 13.4
5 3/4 8.95 61.7 13 1.7 11.7
6 8.7 60.0 13 1/4 1.45 10.0
6 1/4 8.45 58.2 13 1/2 1.2 8.3
6 1/2 8.2 56.5 13 3/4 0.95 6.5
6 3/4 7.95 54.8 14 0.7 4.8
7 7.7 53.1 14 1/4 0.45 3.1
14 1/2 0.2 1.4
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Page 1A-18 90-863757--1 DECEMBER 2001
VACUUM GAUGE VS MAP SENSOR
This graph is correct at sea level only.
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90-863757--1 DECEMBER 2001 Page 1A-19
Centigrade to Fahrenheit Conversion
Centigrade Fahrenheit Centigrade Fahrenheit
-55 -67 85 185
-50 -58 90 194
-45 -49 95 203
-40 -40 100 212
-35 -31 105 221
-30 -22 110 230
-25 -13 115 239
-20 -4 120 248
-15 5 125 257
-10 14 130 266
-5 23 135 275
0 32 140 284
5 41 145 293
10 50 150 302
15 59 155 311
20 68 160 320
25 77 165 329
30 86 170 338
35 95 175 347
40 104 180 356
45 113 185 365
50 122 190 374
55 131 195 383
60 140 200 392
65 149 205 401
70 158 210 410
75 167 215 419
80 176 220 428
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Page 1A-20 90-863757--1 DECEMBER 2001
COVER

2
A
TROUBLESHOOTINGSERVICE MANUAL NUMBER 33
90-863757--1 DECEMBER 2001 Page 2A-1
SECTION 2A - TROUBLESHOOTING
Table of Contents
Troubleshooting Without A Diagnostic Tool 2A-2
Troubleshooting With A Diagnostic Tool 2A-2
Troubleshooting Worksheet 2A-3. . . . . . . . . . .
PCM Calibration Label For
8.1 liter (496 cid) Engines 2A-3. . . . . . . . .
Data Collection 2A-3. . . . . . . . . . . . . . . . . . .
PCM 555/ECM 555 DDT/Rinda
8.1 liter (496 cid)/GM EFI
SCAN TOOL SHEET 2A-4. . . . . . . . . . . . .
Troubleshooting Guides 2A-7. . . . . . . . . . . . . .
Symptom Chart 2A-7. . . . . . . . . . . . . . . . . .
Fault Chart 2A-9. . . . . . . . . . . . . . . . . . . . . . .
Engine Will Not Crank Over 2A-13. . . . . . . .
Mercury MerCruiser Scan Tool
Flowchart 2A-16. . . . . . . . . . . . . . . . . . . . . . .
Digital Diagnostic Terminal Flowchart 2A-17
COVER

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MERCURY MERCRUISER 496 MAG DIAGNOSTICS Service Repair Manual SN:0M000000 and Above

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