The electronic ignition (EI) system controls
the fuel combustion by providing a spark to ignite the compressed air/fuel
mixture at the correct time. To provide optimum engine performance,
fuel economy, and control of the exhaust emissions, the powertrain
control module (PCM) controls the spark advance of the ignition system.
An electronic ignition system has the following advantages over a mechanical
distributor system:
| • | Remote mounting capability |
| • | No mechanical load on the engine |
| • | More coil cool down time between firing events |
| • | Elimination of mechanical timing adjustments |
| • | Increased available ignition coil saturation time |
The EI system does not use the conventional distributor
and coil. The ignition system consists of 3 ignition coils, an ignition
control (IC) module, a camshaft position (CMP) sensor , a 7X crankshaft
position (CKP) sensor in the block, a 24X crankshaft position (CKP)
sensor behind the crankshaft balancer, and the related connecting
wires, ignition control (IC) and fuel metering portion of the PCM.
Conventional ignition coils have one end of the secondary winding connected
to the engine ground. In this ignition system, neither end of the secondary
winding is grounded. Instead, each end of a coil's
secondary winding is attached to a spark plug. Each
cylinder is paired with the cylinder that is opposite
it (1-4, 2-5, 3-6). The 2plugs are
on companion cylinders, i.e., on top dead center at the
same time.
When the coil discharges, both plugs fire at the same time to complete
the series circuit. The cylinder on compression is said to be the event cylinder
and the one on exhaust is the waste cylinder. The
cylinder on the exhaust stroke requires very little
of the available energy to fire the spark plug.
The remaining energy will be used as required by the cylinder
on the compression stroke. The same process is repeated
when the cylinders reverse roles. This method of ignition
is called a waste spark ignition system.
Since the polarity of the ignition coil primary and secondary windings
is fixed, one spark plug always fires with normal polarity and the companion
plug fires with reverse polarity. This differs from
a conventional ignition system that fires all the
plugs with the same polarity. Because the ignition
coil requires approximately 30 percent more voltage
to fire a spark plug with reverse polarity, the ignition
coil design is improved, with the saturation time and
the primary current flow increased. This redesign of
the system allows higher secondary voltage to be available
from the ignition coils - more than 40 kilovolts
(40,000 volts) at any engine RPM. The voltage
required by each spark plug is determined by the
polarity and the cylinder pressure. The cylinder on
compression requires more voltage to fire the spark
plug than the cylinder on exhaust.
It is possible for one spark plug to fire even though a plug wire from
the same coil may be disconnected from the companion plug. The disconnected
plug wire acts as one plate of a capacitor, with
the engine being the other plate. These 2 capacitor
plates are charged as a spark jumps across the
gap of the connected spark plug. The plates are then discharged
as the secondary energy is dissipated in an oscillating
current across the gap of the spark plug that
is still connected. Secondary voltage requirements are
very high with an open spark plug or spark plug wire.
The ignition coil has enough reserve energy to
fire the plug that is still connected at idle, but
the coil may not fire the spark plug under a high
engine load. A more noticeable misfire may be evident under
load, both spark plugs may then be misfiring.
24X and 7X Crankshaft Position Sensors/Harmonic Balancer Interrupter
Ring
The 24X crankshaft position
(CKP) sensor (1), secured in a mounting bracket (3) and bolted
to the front side of the engine timing chain cover (2), is
partially behind the crankshaft balancer.
The 7X crankshaft position (CKP) sensor uses a 2-wire connector
at the sensor and a 3-way connector at the ignition control (IC) module.
The 24X CKP sensor contains a Hall-effect switch. The magnet
and Hall-effect switch are separated by an air gap. A Hall-effect
switch reacts like a solid state switch, grounding
a low current signal voltage when a magnetic
field is present. When the magnetic field is
shielded from the switch by a piece of steel placed
in the air gap between the magnet and
the switch, the signal voltage is not grounded. If the
piece of steel, called an interrupter, is repeatedly
moved in and out of the air gap, the signal
voltage will appear to go ON-OFF, ON-OFF,
ON-OFF. Compared to a conventional mechanical distributor,
this ON-OFF signal is similar to the signal
that a set of breaker points in the distributor
would generate as the distributor shaft turned and the
points opened and closed.
In the case of the electronic ignition system, the piece of steel is
a concentric interrupter ring mounted to the rear of the crankshaft balancer.
The interrupter ring has blades and windows
that, with crankshaft rotation, either
block the magnetic field or allow the field to reach the Hall-effect
switch. The Hall-effect switch is called
a 24X CKP sensor because the interrupter ring has 24 evenly
spaced blades and windows. The 24X CKP
sensor produces 24 ON-OFF pulses per crankshaft
revolution.
The interrupter ring is a special wheel cast on the crankshaft that
has 7 machined slots, 6 of which are equally spaced 60 degrees apart.
The seventh slot is spaced 10 degrees
from one of the other slots. As the interrupter
ring rotates with the crankshaft, the slots change the
magnetic field. This will cause the 7X
to ground the 3X signal voltage that is
supplied by the ignition control module (ICM) . The ICM
interprets the 7X ON-OFF signals as an indication
of crankshaft position. The ICM must
have the 7X signal to fire the correct ignition
coil.
The 7X interrupter ring and the Hall-effect switch react similarly.
The 24X signal is used for better resolution at a calibrated RPM.
Camshaft Position (CMP) Sensor
The camshaft position
(CMP) sensor is located on the timing cover behind the water pump near the
camshaft sprocket. As the camshaft sprocket turns, a magnet in the
sprocket activates the Hall-effect switch in the camshaft position
(CMP) sensor. When the Hall-effect switch is activated, the switch
grounds the signal line to the PCM, pulling the CMP sensor
signal circuit's applied voltage low. This is interpreted as a CAM
signal.
The CAM signal is created as piston #1 is on the intake stroke. If
the correct CAM signal is not received by the PCM, DTC P0341 will
be set.
Ignition Coils
Three twin-tower ignition coils are individually mounted to the ICM.
Each coil provides spark for 2 plugs simultaneously,
called waste spark distribution. Each
coil is serviced separately. Two terminals connect each coil
pack to the module. Each coil is provided
a fused ignition feed. The other terminal at
each coil is individually connected to the module, which
will energize one coil at a time by completing
and interrupting the primary circuit ground
path to each coil at the proper time.
Ignition Control Module (ICM)
The ICM performs the
following functions:
| • | The ICM determines the correct ignition coil firing sequence based
on the 7X pulses. This coil sequencing occurs at start-up. After the engine
is running, the ICM determines the sequence
and continues triggering the ignition
coils in the proper sequence. |
| • | The ICM sends the 3X crankshaft reference (fuel control) signal
to the PCM. The PCM determines the engine RPM from this signal. This signal
is also used by the PCM to determine
crankshaft speed for the IC spark advance calculations. |
The 3X reference signal sent to the PCM by the ICM is an ON-OFF pulse
occurring 3 times per crankshaft revolution.
Circuits Affecting Ignition Control
In order to properly control the ignition timing, the PCM relies on
the following information:
| • | The engine load (manifold pressure or vacuum) |
| • | The barometric pressure (BARO) |
| • | The intake air temperature |
| • | The crankshaft position |
The ignition control (IC) system consists of the following components:
| • | The ignition control module |
| • | The 7X crankshaft position sensor |
| • | The 24X crankshaft position sensor |
| • | The powertrain control module |
| • | All of the connecting wires |
The electronic ICM connector terminals are identified as shown in the
electronic ignition (EI) system graphic. These circuits
perform the following functions:
| • | 3X reference high--The 7X CKP sensor sends a signal to the
ICM which generates a reference pulse
that is sent to the PCM. The PCM uses this signal to calculate
the crankshaft position and the engine speed, and
to trigger the fuel injectors. |
| • | 3X reference low--This wire is grounded through the ICM
and assures the ground circuit has no voltage drop between the ICM and
the PCM. |
| • | Ignition control bypass--During initial cranking, the PCM
will look for synchronizing pulses from the CMP sensor and
the 7X CKP sensor. The pulses indicate the
position of the #1 piston and the #1 intake
valve. Five volts is applied to the bypass
circuit at precisely the same time these signals are received
by the PCM. This generally occurs within
one or two revolutions of the crankshaft.
An open or grounded bypass circuit will set a DTC P1351
and the engine will run at base ignition
timing. A small amount of spark advance is
built into the ICM to enhance performance. |
| • | Ignition control (IC)--The PCM uses this circuit to trigger
the electronic ignition control module. The PCM uses the crankshaft reference
signal to calculate the amount of spark
advance needed. |
| • | 24X reference signal--The 24X crankshaft position (CKP)
sensor increases idle quality and low speed driveability by providing better
resolution at a calibrated RPM. |
Ignition System
There are important considerations to point out when servicing the
ignition system. The following noteworthy Information will list some of these
to help the technician in servicing the
ignition system.
| • | The ignition coils' secondary voltage output capabilities are
more than 40,000 volts. Avoid body contact with ignition
high voltage secondary components when the
engine is running or personal injury may
result. |
| • | The 7X CKP sensor is the most critical part of the ignition system.
If the sensor is damaged so that pulses are not generated,
the engine will not start. |
| • | CKP sensor clearance is very important! The sensor must not contact
the rotating interrupter ring at any time, or sensor damage
will result. If the balancer interrupter ring
is bent, the interrupter ring blades will
destroy the sensor. |
| • | The ignition timing is not adjustable. There are no timing marks
on the crankshaft balancer or the timing chain cover. |
| • | If CKP sensor replacement is necessary, the crankshaft balancer
must be removed first. The balancer is a press-fit onto the crankshaft.
Removing the serpentine accessory drive
belt and the balancer attaching bolt will
allow the sensor's removal with the J 38197-A
balancer remover. When reinstalled, the
proper tightening of the balancer attachment bolt is critical
to ensure the balancer stays attached
to the crankshaft. |
| • | If a CKP sensor assembly is replaced, check the crankshaft balancer
interrupter ring for any bent blades. If this is
not checked closely and a bent blade exists, the new
CKP sensor can be destroyed by the bent
blade with only one crankshaft revolution. |
| • | Neither side of the ignition coil primary or secondary windings
is connected to engine ground. Although the ignition coil packs are secured
to the IC module, this is not an electrical
connection to ground. |
| • | Be careful not to damage the secondary ignition wires or the
boots when servicing the ignition system. Rotate each boot to dislodge the
boot from the plug or coil tower before
pulling the boot from either a spark plug or the
ignition coil. Never pierce a secondary ignition
wire or boot for any testing purposes. Future
problems are guaranteed if pinpoints or test
lamps are pushed through the insulation for testing. |
| • | The IC module is grounded to the engine block through 3 mounting
studs used to secure the ICM to the mounting bracket. If service
is required, ensure that good electrical contact
is made between the ICM and the mounting
bracket, including the proper hardware and torque. |
| • | A conventional tachometer used to check the RPM on a primary
ignition tach lead will not work on this ignition system. In order to monitor
the RPM, use a scan tool. |
Powertrain Control Module (PCM)
The powertrain control
module (PCM) is responsible for maintaining the proper spark and fuel injection
timing for all driving conditions. To provide
optimum driveability and emissions, the PCM monitors
input signals from the following components in
calculating the ignition control (IC) spark
timing:
| • | The ignition control module (ICM) |
| • | The engine coolant temperature (ECT) sensor |
| • | The intake air temperature (IAT) sensor |
| • | The mass air flow (MAF) sensor |
| • | The transaxle range inputs from the transaxle range switch |
| • | The throttle position (TP) sensor |
| • | The vehicle speed sensor (VSS) |
Modes of Operation
Ignition control (IC) spark timing is the PCM's method of controlling
the spark advance and the ignition dwell when the ignition system is
operating in the IC mode. There are 2
modes of ignition system operation:
In Bypass mode, the ignition system operates independently of the PCM,
with Bypass mode spark advance always at 10 degrees BTDC. The PCM has
no control of the ignition system when
in this mode. In fact, the PCM could be disconnected
from the vehicle and the ignition system would still
fire the spark plugs, as long as the
other ignition system components are functioning. This would
provide spark but no fuel injector pulses, and the
engine will not start in this situation. The PCM switches
to the IC mode and PCM controlled spark advance
as soon as the engine begins cranking.
After the switch is made to IC mode, the mode will stay
in effect until one of the following conditions
occur:
| • | The engine is turned OFF |
| • | The engine quits running |
| • | A PCM/ICM fault (DTC P1351, P1352, P1361, or P1362) is
detected |
If a PCM/ICM fault is detected while the engine is running, the ignition
system will switch to Bypass mode operation. The engine may quit running,
but will restart and stay in Bypass mode
with a noticeable loss of performance.
In the IC mode, the ignition spark timing and the ignition dwell time
is fully controlled by the PCM. The IC spark advance and the ignition dwell
is calculated by the PCM using the following
inputs:
| • | The engine speed (24X reference or 3X reference). |
| • | The crankshaft position (24X reference or 3X reference and camshaft
position PCM input signal). |
| • | The engine coolant temperature (ECT) sensor |
| • | The throttle position (TP) sensor |
| • | The knock sensor (KS) signal |
| • | The Park/Neutral position switch input |
| • | The vehicle speed sensor (VSS) input |
| • | The PCM and ignition system supply voltage |
The following describes the PCM to ICM circuits:
| • | The 3X reference input. The ignition control module (ICM) generates
the 3X reference signal from the 7X CKP sensor. The ICM sends the
3X reference signal to the PCM. The PCM uses this signal to calculate
the engine RPM and the crankshaft position at speeds of more than 1600 RPM.
If the PCM receives no pulses on this
circuit, the PCM will use the 24X reference pulses to calculate the
RPM and the crankshaft position. The engine will continue
to run and start normally as long as the 7X CKP sensor pulses are
being received, but DTC P1374 will be set. |
| • | The 24X reference input. The 24X CKP sensor generates the 24X
reference signal to calculate the engine speed and the crankshaft position
at engine speeds of less than 1600 RPM. The 24X reference
signal provides better resolution within the calibrated RPM range.
This increases the idle quality and the low speed driveability. When
the engine speed exceeds 1600 RPM, the PCM begins using the
3X reference signal to control the spark timing. If the 24X reference
signal is not received by the PCM while the engine is running, DTC P0336
will be set and the 3X reference will be used to control the spark
advance under 1600 RPM. Bypass mode will be initiated under
400 RPM. The engine will continue to run and start normally. |
| • | The reference low input. The reference low circuit establishes
a common ground between the ICM and the PCM. The wire is connected
to engine ground only through the ICM. The circuit minimizes any
electrical ground differences between the PCM and the ICM. The PCM
uses the reference low circuit to clearly recognize the 3X reference
signals. If the circuit is open, or connected to ground at the PCM,
the circuit may cause poor engine performance and possibly illuminate the
malfunction indicator lamp (MIL) with no DTC. |
| • | The knock sensor (KS) input. The PCM contains integrated KS diagnostic
circuitry. The KS system is comprised of the KS, PCM, and the related wiring.
The PCM monitors the KS signal in order to detect engine detonation.
When spark knock occurs, the PCM retards the spark timing (IC) to
reduce detonation. A retarded spark timing may also be the result
of excessive engine mechanical or transaxle noise. If a KS signal
is found varying within the average voltage, DTC P0327 may set. |
| • | The Bypass signal output. The ICM controls spark timing until
the PCM detects a calibrated number of 3X reference pulses (Bypass mode).
When the PCM receives these pulses, the PCM then provides 5.0 volts
to the ICM on the bypass circuit. This signals the IC module to
transfer spark timing control the PCM (IC mode). Proper sequencing
of the 3 ignition coils, i.e. which coil to fire, is always the job
of the ICM. If the PCM detects a short to voltage on the bypass circuit,
DTC P1362 will set. An open in the bypass circuit will set
DTC P1352. |
| • | The ignition control (IC) output. The PCM sends out timing pulses
to the ICM on the IC circuit. When the ignition system is in the
Bypass mode and the PCM has not sent the 5.0 volt bypass signal, the
IC module grounds these pulses. When the IC mode is initiated and
the PCM has supplied the bypass signal, these pulses are sent to
the ICM to control the ignition spark timing. If the IC circuit is
grounded when the engine is started, DTC P1361 will set
and the ignition system will stay in the Bypass mode. If the IC circuit
becomes open or grounded during IC mode operation, DTC P1351
or P1361 may set. When this happens, the engine will quit running
but will restart. Upon restart following an ignition cycle, DTC P1361
will be set and the ignition system will operate in Bypass mode. |
