Mercury 305 CID, Service Manual, Page: 542 / 967

ELECTRONIC FUEL INJECTION (MULTI-PORT AND THROTTLE BODY) - 5E-1 90-823225--1 1096
General Information
! CAUTION
To reduce the chance of personal injury and/or
property damage, the following instructions
must be carefully observed: proper service and
repair are important to the safety of the service
technician and the safe, reliable operation of all
MerCruiser Electronic Fuel Injection (Multi-Port
And Throttle Body) equipped engines. If part re-
placement is necessary, the part must be re-
placed with one of the same part number or with
an equivalent part. Do not use a replacement part
of lesser quality. The service procedures recom-
mended and described in this service manual are
effective methods of performing service and re-
pair. Some of these procedures require the use of
tools specially designed for the purpose. Ac-
cordingly, anyone who intends to use a replace-
ment part, service procedure or tool, which is not
recommended by the system manufacturer,
must first determine that neither his safety nor
the safe operation of the engine will be jeopar-
dized by the replacement part, service procedure
or tool selected. It is important to note that this
manual contains various “Cautions” and
“Notes” that must be carefully observed in order
to reduce the risk of personal injury during ser-
vice or repair, or the possibility that improper ser-
vice or repair may damage the engine or render
it unsafe. It is also important to understand that
these “Cautions” and “Notes” are not exhaus-
tive, because it is impossible to warn of all the
possible hazardous consequences that might re-
sult from failure to follow these instructions.
Introduction
The following manual has been prepared for effective
diagnosis of the MerCruiser Electronic Fuel Injection
system.
All information, illustrations and specifications con-
tained in this manual are based on the latest product
information available at the time of publication ap-
proval. The right is reserved to make changes at any
time without notice.
An understanding of the material contained herein
and in subsequent publications issued when neces-
sary, will assist service personnel in properly main-
taining the quality to which MerCruiser engine control
systems are built.
Visual/Physical Inspection
A careful visual and physical inspection must be
performed as part of any diagnostic procedure.
This can often lead to fixing a problem without
further steps. Inspect all vacuum hoses for correct
routing, pinches, cuts, or disconnects. Be sure to in-
spect hoses that are difficult to see. Inspect all the
wires in the engine compartment for proper connec-
tions, burned or chafed spots, pinched wires, or con-
tact with sharp edges or hot exhaust manifolds. This
visual/physical inspection is very important. It must
be done carefully and thoroughly.
Basic Knowledge and Tools Required
To use this manual most effectively, a general under-
standing of basic electrical circuits and circuit testing
tools is required. You should be familiar with wiring
diagrams; the meaning of volts, ohms and amperes;
the basic theories of electricity; and understand what
happens in an open or shorted wire. To perform sys-
tem diagnosis, several special tools and equipment
are required. Please become acquainted with the
tools and their use before attempting to diagnose the
system. Special tools which are required for system
service are listed later in this section (see “Table of
Contents”).
Electrostatic Discharge Damage
Electronic components used in control systems are
often designed to carry very low voltage, and are very
susceptible to damage caused by electrostatic dis-
charge. It is possible for less than 100 volts of static
electricity to cause damage to some electronic com-
ponents. 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 stati-
cally charged. The most common methods of charg-
ing 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 per-
son with well-insulated shoes stands near a highly
charged object and momentarily touches ground.
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;
therefore, it is important to use care when handling
and testing electronic components.