G424F(FE) Service Manual Chapter 5. Engine Management System (EMS) 143
There are multiple limp-home modes available with
electronic throttle control:
1. If the throttle itself is suspected of being
inoperable, the SECM will remove the power to
the throttle motor. When the power is removed,
the throttle blade returns to its “default” position,
approximately 7% open.
2. If the SECM can still control the throttle but some
other part of the system is suspected of failure,
the SECM will enter a “Reduced Power” mode. In
this mode, the power output of the engine is
limited by reducing the maximum throttle position
allowed.
3. In some cases, the SECM will shut the engine
down. This is accomplished by stopping ignition,
turning off the fuel, and disabling the throttle.
Picture courtesy of Robert Bosch GmbH
Figure 15. Throttle Body Assembly Exploded View
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 *
(sequential ignition or fuel injection only)
• Cam timing wheel *
(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
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