Ignition System Overview
The ignition system consists of the following components or circuits:
| • | The 8 ignition secondary wires |
| • | The 8 ignition control (IC) circuits |
| • | The camshaft position (CMP) sensor |
| • | The camshaft reluctor wheel |
| • | The crankshaft position (CKP) sensor |
| • | The crankshaft reluctor wheel |
| • | The related connecting wires |
| • | The powertrain control module (PCM) |
Crankshaft Position Sensor and Reluctor Wheel
The crankshaft position (CKP) sensor is a magneto resistive type sensor.
The CKP sensor works in conjunction with a 24X reluctor wheel.
The reluctor wheel is mounted on the rear of the crankshaft. The
24X reluctor wheel uses 2 different width notches that
are 15 degrees apart. This pulse width encoded pattern allows cylinder
position identification within 90 degrees of crankshaft
rotation. In some cases identification can be achieved within 45 degrees
of crankshaft rotation. The reluctor wheel also has dual track
notches that are 180 degrees out of phase. This design allows for
quicker starts and accuracy. The CKP sensor also outputs a 4X signal
for spark control, for misfire diagnosis, for tachometer output, and for fuel
control. All CKP signals are output as a digital square waveform.
Camshaft Position Sensor
The camshaft position (CKP) sensor works in conjunction with 1X reluctor
wheel mounted at the rear of the camshaft. The CMP is used to determine the
top dead center position of cylinder #1, and will synchronize with
the 24X CKP sensor signal for quicker starting. The PCM will detect
an increase in the mass airflow (MAF) sensor signal when the engine starts.
The CMP signals are output as a digital waveform.
Ignition Coils
The ignition system on this vehicle features a multiple coil configuration
and is known as coil near plug. There are 2 styles of ignition
coil assemblies . The engine could have either style of coil assembly.
The ignition coil mounting bracket is attached to the rocker cover .
The 8 ignition coils are individually mounted above each
cylinder on the rocker covers. The coils are fired sequentially.
There is an ignition control (IC) circuit for each ignition coil.
The 8 ignition control circuits are connected to the PCM.
The PCM triggers each ignition coil individually, and makes all timing
decisions. The ignition coils are supplied with the following circuits:
| • | The ignition 1 voltage circuit |
| • | The ignition control circuit |
| • | The reference low circuit |
The ignition 1 voltage circuits are fused separately for each
bank of the engine. The 2 fuses also supply the power for the injectors
for that bank of the engine. Each coil is serviced separately.
This system distributes very high ignition energy for plug firing. Less
energy is lost to the ignition wire resistance because the ignition wires
are much shorter than in a conventional ignition system.
Circuits Affecting Ignition Control
In order to properly control the ignition timing, the PCM relies on
the following information:
| • | The engine load, based on the manifold pressure or vacuum |
| • | The atmospheric or barometric pressure (BARO) |
| • | The intake air temperature (IAT) |
| • | The crankshaft position |
The ignition control (IC) system consists of the following components:
| • | The 24X crankshaft position (CKP) sensor |
| • | The powertrain control module (PCM) |
The ignition control uses the following signals and circuits in order
to control the spark timing functions:
| • | The 24X signal--The 24X crankshaft position sensor sends
a signal to the PCM. The PCM uses this signal in order to determine the crankshaft
position. The PCM also utilizes this signal in order to trigger
the fuel injectors. |
| • | The ignition control (IC) circuits--The PCM uses these circuits
in order to trigger the ignition coils. |
Ignition Information
There are important considerations to point out when servicing the ignition
system. The following information will list some of these considerations,
in order to help the technician service the ignition system.
| • | The ignition coils secondary voltage output capabilities are very
high--more than 40,000 volts. Avoid physical contact with the
ignition high voltage secondary components when the engine is
running, or personal injury may result. |
| • | The 24X crankshaft position (CKP) sensor is the most critical
part of the ignition system. If the sensor is damaged so that pulses are not
generated, the engine does not start. |
| • | The CKP sensor clearance is very important. If the interrupter
ring is bent or damaged in any way, the CKP sensor may be destroyed. Extreme
care must be exercised during removal and installation procedures. |
| • | The ignition timing is not adjustable. There are no timing marks
on the crankshaft balancer or the timing chain cover. |
| • | When you service the ignition system, do NOT damage the secondary
ignition wires or the boots. Before you pull the boot from the spark plug
or from the ignition coil, rotate each boot in order to dislodge
the boot from the plug or from the coil tower |
Powertrain Control Module (PCM)
The PCM is responsible for maintaining proper spark and fuel injection
timing for all driving conditions. In order to provide the optimum driveability
and emissions control, the PCM monitors the input signals from
the additional following components in order to calculate the ignition
control (IC) spark timing:
| • | The engine coolant temperature (ECT) sensor |
| • | The intake air temperature (IAT) sensor |
| • | The mass air flow (MAF) sensor |
| • | The trans range inputs from the transmission range switch (PRND) |
| • | The throttle position (TP) sensor |
| • | The vehicle speed sensor (VSS) |
