The electronic ignition system controls 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 exhaust emissions, the PCM controls the spark advance of the ignition
system.
Electronic ignition 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 electronic ignition system does not use the conventional
distributor and coil. The ignition system consists of three ignition coils,
an ignition control module, a camshaft position (CMP) sensor,
7X crankshaft position (CKP) sensor in the block, a 24X CKP sensor
behind the crankshaft balancer, related connecting wires, and the 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 on the
opposite side (1 and 4, 2 and 5, 3 and 6). These two plugs
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 saturation time and
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 one on exhaust.
One spark plug may 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 two 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 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 CKP sensor uses a two wire connector at the sensor and a three-way
connector at the ignition control 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 seven machined slots, six 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. The ignition control
module interprets the 7X on-off signals as an indication
of crankshaft position. The ignition control
module must have the 7X signal to fire the
correct ignition coil.
The 7X interrupter ring and 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 CMP sensor. When
the Hall-effect switch is activated, the signal line to the PCM is grounded,
pulling the CMP sensor signal circuits 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 ignition
control module. Each coil provides spark for two
plugs simultaneously (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 (IC) Module
The ignition control
(IC) module performs the following functions:
| • | Determines the correct ignition coil firing sequence, based on
7X pulses--This coil sequencing occurs at start-up. After the engine
is running, the module determines the
sequence, and continues triggering the
ignition coils in proper sequence. |
| • | Sends the 3X crankshaft reference (fuel control) signal to the
PCM--The PCM determines engine RPM from this signal. this signal is also
used by the PCM to determine crankshaft
speed for ignition control (IC) spark
advance calculations. |
The 3X reference signal sent to the PCM by the IC module is an on,
off pulse occurring 3 times per crankshaft revolution.
Circuits Affecting Ignition Control
In order to properly control ignition timing, the PCM relies on the
following information:
| • | Engine load (manifold pressure or vacuum) |
| • | Atmospheric (barometric) pressure |
The IC system consists of the following components:
The electronic IC module connector terminals are identified as shown
in the Electronic Ignition System graphic. These circuits
perform the following functions:
| • | 3X reference high--The 7X crankshaft position sensor sends
a signal to the electronic ignition control module which generates a reference
pulse that is sent to the PCM. The PCM uses
this signal to calculate crankshaft position
and engine speed (also used 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 camshaft position sensor and
the 7X crankshaft position 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 ignition control
module 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 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
very high - 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 crankshaft position 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. |
| • | Crankshaft position 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. |
| • | Ignition timing is not adjustable. There are no timing marks
on the crankshaft balancer or timing chain cover. |
| • | If crankshaft position 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 balancer
attaching bolt will allow removal with the special
tool J 38197-A
Balancer
Remover. When reinstalled, proper torquing of
the balancer attachment bolt is critical to ensure
the balancer stays attached to the crankshaft. |
| • | If a crankshaft position sensor assembly is replaced, inspect
the crankshaft balancer interrupter ring for any blades being bent. If this
is not inspected closely and a bent blade
exists, the new crankshaft position 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, there is not an electrical
connection to ground. |
| • | Be careful not to damage the secondary ignition wires or 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 lights are pushed
through the insulation for testing. |
| • | The IC module is grounded to the engine block through 3 mounting
studs used to secure the module to the mounting bracket. If servicing
is required, ensure that good electrical contact
is made between the module and the mounting
bracket, including proper hardware and torque. |
| • | A conventional tachometer used to check RPM on a primary ignition
tach lead will not work on this ignition system. In order to check RPM, use
a Scan Tool. |
Powertrain Control Module (PCM)
The PCM is responsible
for maintaining 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 ignition control
(IC) spark timing:
| • | Engine Coolant Temperature (ECT) sensor |
| • | Intake Air Temperature (IAT) sensor |
| • | Mass Air Flow (MAF) sensor |
| • | Trans Range inputs from Transaxle Range switch |
| • | Throttle Position (TP) sensor |
| • | Vehicle Speed Sensor (VSS) |
Modes of Operation
Ignition Control (IC) spark timing is the PCMs method of controlling
spark advance and ignition dwell when the ignition system is operating
in the IC Mode. There are two modes of
ignition system operation:
In Bypass Mode, the ignition system operates independently of the PCM,
with Bypass Mode spark advance always at 10 (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 were functioning. (This
would provide spark but no fuel injector pulses.
The engine will not start in this situation.)
The PCM switches to IC Mode (PCM controlled
spark advance) as soon as the engine begins cranking.
After the switch is made to IC Mode, the IC Mode
will stay in effect until one of the following
conditions occur:
| • | The engine is turned off. |
| • | The engine quits running. |
| • | A PCM/IC module fault (DTC P1351, P1352, P1361, or P1362)
is detected. |
If a PCM/IC module 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 ignition dwell time is
fully controlled by the PCM. IC spark advance and ignition dwell is calculated
by the PCM using the following inputs:
| • | Engine speed (24X reference or 3X reference) |
| • | Crankshaft position (24X reference or 3X reference and Camshaft
position PCM input signal) |
| • | Engine Coolant Temperature (ECT) sensor |
| • | Throttle Position (TP) sensor |
| • | Knock Signal (Knock Sensor) |
| • | Park/Neutral Position (PRNDL input) |
| • | Vehicle Speed (Vehicle Speed Sensor) |
| • | PCM and ignition system supply voltage |
The following describes the PCM to ignition control module circuits:
| • | 3X reference PCM input--The ignition control (IC) module
generates the 3X reference signal from the 7X CKP Sensor. The IC module sends
the 3X reference signal to the PCM. The PCM uses this signal to calculate
engine RPM and crankshaft position at speeds above 1600 RPM.
If the PCM receives no pulses on this circuit,
the PCM will use the 24X reference pulses to calculate RPM and crankshaft
position. The engine will continue to run and start normally
as long as 7X CKP Sensor pulses are being received, but DTC P1374
will be set. |
| • | 24X reference PCM input--The 24X CKP Sensor generates the
24X reference signal to calculate engine speed and crankshaft position at
engine speeds below 1600 RPM. The 24X reference signal provides better
resolution within the calibrated RPM range. This increases idle quality
and low speed driveability. When engine speed exceeds 1600 RPM, the
PCM begins using the, 3X reference signal to control spark timing.
If the 24X reference signal is not received by the PCM while the
engine is running, a DTC P0336 will be set and 3X reference
will be used to control spark advance under 1600 RPM, and Bypass Mode
will be in effect under 400 RPM. The engine will continue to run
and start normally. |
| • | Reference low PCM input--The reference low circuit establishes
a common ground between the ignition control module and the PCM. The wire
is connected to engine ground only through the ignition control module.
The circuit minimizes electrical ground differences between the PCM
and the IC module. 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 a MIL (Service Engine Soon) without a DTC. |
| • | Knock Sensor (KS) PCM input--The PCM contains integrated
knock sensor diagnostic circuitry. The KS system is comprised of the knock
sensor, PCM, and related wiring. The PCM monitors the knock sensor
signal to detect engine detonation. When spark knock occurs, the PCM
retards the spark timing (IC) to reduce detonation. 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
a DTC P0327 may set. |
| • | Bypass signal PCM output--The IC module 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 IC module 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 ignition control module. 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. |
| • | Ignition Control (IC) PCM output--The PCM sends out timing
pulses to the IC module on the IC Circuit. When the ignition system is in
the Bypass mode (the PCM has not sent the 5.0 volt bypass signal),
the IC module grounds these pulses. When the IC Mode (the PCM has
supplied the bypass signal), these pulses are sent to the IC module
to control 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 P1361wil be set,
and the ignition system will operate in Bypass Mode. |
