Suzuki 2007 XL7, Service Manual

Page: 865 / 3159

Ignition System: 1H-1
Ignition System
General Description
Electronic Ignition (EI) System Description
The electronic ignition (EI) system produces and
controls a high-energy secondary spark. This spark is
used to ignite the compressed air/fuel mixture at
precisely the correct time. This provides optimal
performance, fuel economy, and control of exhaust
emissions. This ignition system uses an individual coil
for each cylinder. The ignition coils are mounted in the
center of each camshaft cover with short integrated
boots connecting the coils to the spark plugs. The driver
modules within each ignition coil are commanded ON/
OFF by the engine control module (ECM). The ECM
primarily uses engine speed, the MAF sensor signal, and
position information from the crankshaft position (CKP)
and the camshaft position (CMP) sensors. This controls
the sequence, dwell, and timing of the spark. The EI
system consists of the following components:
Crankshaft Position (CKP) Sensor
The crankshaft position (CKP) sensor works in
conjunction with a 58 tooth reluctor wheel on the
crankshaft. The engine control module (ECM) monitors
the voltage frequency on the CKP sensor signal circuit.
As each reluctor wheel tooth rotates past the sensor, the
sensor creates a digital ON/OFF pulse. This digital
signal is processed by the ECM. The reluctor wheel
teeth are 6 degrees apart. Having only 58 teeth leaves a
12 degree span that is uncut. This creates a signature
pattern that enables the ECM to determine the CKP. The
ECM uses the signal to determine which pair of cylinders
is approaching top dead center based on the CKP signal
alone. The camshaft position (CMP) sensor signals are
used in order to determine which of these 2 cylinders is
on a firing stroke, and which is on the exhaust stroke.
The ECM uses this to properly synchronize the ignition
system, the fuel injectors, and the knock control. This
sensor is also used in order to detect misfire. The CKP
sensor uses the following circuits:
• A 5-volt reference circuit
• A signal circuit
• A low reference circuit
Camshaft Position (CMP) Sensor
This engine uses 4 camshaft position (CMP) sensors,
one for each camshaft. The CMP sensor signals are a
digital ON/OFF pulse, output 4 times per revolution of
the camshaft. The CMP sensor does not directly affect
the operation of the ignition system. The CMP sensor
information is used by the engine control module (ECM)
to determine the position of the 4 camshafts relative to
the crankshaft position. By monitoring the CMP and
crankshaft position (CKP) signals the ECM can
accurately time the operation of the fuel injectors. The
ECM supplies the CMP sensor with a 5-volt reference
circuit and a low reference circuit. The CMP sensor
signals are an input to the ECM. These signals are also
used to detect camshaft alignment with the crankshaft.
Ignition Coils
Each ignition coil contains a solid state driver module as
its primary element. The engine control module (ECM)
signals the coil driver to initiate a firing event by applying
ignition control (IC) circuit voltage for the appropriate
time, or dwell. When the voltage is removed the coil fires
the spark plug. The ignition coils use the following
circuits:
• An ignition voltage supply circuit
• An IC circuit
• Two ground circuits
Engine Control Module (ECM)
The engine control module (ECM) controls all ignition
system functions, and constantly corrects the spark
timing. The ECM monitors information from various
sensor inputs that include the following components:
• The throttle position (TP) sensor
• The engine coolant temperature (ECT) sensor
• The mass air flow (MAF) sensor
• The intake air temperature (IAT) sensor
• The vehicle speed sensor (VSS)
• The transmission gear position or range information
sensors
• The engine knock sensors (KS)
• Ambient pressure sensor (BARO)