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GENERAL DESCRIPTION
IGNITION SYSTEM
This vehicle uses a full–transistor type, direct–ignition
system, comprising of (3) ignition coils, (3) spark plugs
and the Engine Control Module or ECM. The ECM also
has the function of controlling the automatic transmis-
sion shift points, if vehicle is so equipped.
In this direct ignition systems, the ECM has the function
of the distributor. Because the ECM is solid state, there
is no moving parts (such as in a distributor) and wear
items are eliminated, simplifying tune up procedures.
Each of the three ignition coils are placed directly on a
spark plug, thereby eliminating the high–tension cables
(spark plug wires). Both distributor and plug wires are
eliminated with this direct ignition system.
The ECM has a self–diagnostic mode to detect abnormal
input signals as a means of component fault detection.
By reviewing abnormal (out of normal range) ECM
inputs, the diagnostic mode usually indicates which com-
ponent has failed and speeds the repair time.
The ECM also has a fail-safe (limp home) mode which
allows minimal engine function in the unlikely event of
ECM failure.
ECM
5V
IT
IT1 21
IT2 20
IT3 19
ITI∼3
1 CIRCUIT FOR
EACH TERMINAL
W/B
W
W/R
+12V
(VIA IG SW)
SPARK PLUGS
#1
#2
#3
COLOR CODE
W – WHITE
B – BLACK
R – RED
IGNITION COIL
The ignition coils provide the high voltage necessary for
ignition. They function similar to a normal (single coil)
system with the difference of each coil being individually
placed over a spark plug. The coil windings are protected
by a molded plastic housing with weather–resistant wir-
ing connections.
Each coil also contains power transistors which provide
current switching and amplification.
When the ECM (Engine Control Module) allows the base
current (IT signal) to flow to a transistor, the collector cur-
rrent flows and passes through the ignition coil primary
circuit side.
When the IT signal is switched off while current is pass-
ing through the primary coil, (current is abruptly shut off),
a self–induction condition occurs and reverse electo-
magnetic force is generated. In conjection, mutual
induction action operates and high voltage is generated
by the secondary coil, producing current to the spark
plug.
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