G424F(FE) Service Manual Chapter 4. Engine Electrical System 102
Ignition System
Spark-ignited engines require accurate control of
spark timing and spark energy for efficient
combustion. The MI-07 ignition system provides this
control. The system consists of the following
components:
• SECM
• Ignition coil drivers *
• Ignition coil(s) *
• Crankshaft position sensor *
• Crankshaft timing wheel *
• Cam position sensor *
(for sequential ignition or fuel injection only)
• Cam timing wheel *
(for sequential ignition or fuel injection only)
• Spark plugs *
The SECM, through use of embedded control
algorithms and calibration variables, determines the
proper time to start energizing the coil and fire the
spark plug. This requires accurate crank/camshaft
position information, an engine speed calculation,
coil energy information, and target spark timing. The
SECM provides a TTL compatible signal for spark
control. The coil must contain the driver circuitry
necessary to energize the primary spark coil
otherwise an intermediary coil driver device must be
provided. The SECM controls spark energy (dwell
time) and spark discharge timing.
Wasted Spark DIS Ignition System
The G424F and G424FE engine has a wasted spark
ignition system (2 cylinders per coil).
Wasted spark ignition is a type of distributor-less
ignition system where a pair of multi tower coils is
mounted near the spark plugs. The DIS system
eliminates the wear associated with most distributor
type ignition systems. The wasted spark ignition
fires pairs of cylinders at each ignition event. One
cylinder fires on the compression stroke as is normal.
However, the complementary pair in the firing order
is fired simultaneously while that particular cylinder
is on the exhaust stroke. Since the ionized exhaust
gases require little spark energy, the majority of the
ignition energy from the coil goes to the spark plug
in the cylinder on the compression stroke.
The DIS coil pack can be mounted close to the
spark plugs, thereby improving ignition lead routing
and length. There are fewer parts to malfunction on
the DIS system when compared to a distributor type
system.
DIS COMPONENTS
In a typical DIS ignition system, a crankshaft
position sensor generates a basic timing signal by
reading notches on the crankshaft, flywheel, or
harmonic balancer. The crank sensor signal goes to
the small engine control module (SECM), where it is
used to determine firing order and turn the individual
ignition coils on and off.
The operation of the ignition system is essentially
the same as any other ignition system. Each coil has
a low primary resistance (0.4 to 0.6 ohms) and steps
up the primary system voltage from 12 volts to as
much as 40,000 volts to produce a spark for the
spark plug.
It is a direct connection that delivers the hottest
spark possible. Resistor plugs are generally used to
suppress electromagnetic interference (EMI).
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