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 Sensor, 7X Crankshaft
Position Sensor in the block, a 24X Crankshaft Position 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 opposite it (1-4,
2-5, 3-6). 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 its 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% 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--greater
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.
It is possible for one spark plug to fire even though a plug wire from
the same coil may be disconnected from its 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
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 sensor uses a two wire connector at the
sensor and a three-way connector at the ignition control module.
The 24X crankshaft position sensor contains a Hall-effect switch.
The magnet and Hall-effect switch are separated by an air gap. A Hall-ffect
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 it to reach the Hall-effect
switch. The Hall-effect switch is called a 24X crankshaft
position sensor, because the interrupter ring
has 24 evenly spaced blades and windows. The
24X crankshaft position 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
sensor is located on the timing cover behind the water pump near the camshaft
sprocket. As the camshaft sprocket turns, a magnet in it activates the
Hall-effect switch in the camshaft position sensor. When the Hall-effect
switch is activated, it grounds the signal line to the PCM, pulling
the camshaft position 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 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:
| • | It 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. |
| • | It 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 Ignition Control (IC) system consists of the following components:
| • | Ignition control module |
| • | 7X crankshaft position sensor |
| • | 24X crankshaft position sensor |
| • | Powertrain control module |
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 its removal
with 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, check the
crankshaft balancer interrupter ring for any blades being bent. If this is
not checked 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, it 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 it from the
plug or coil tower before pulling it 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 its mounting bracket. If servicing
is required, ensure that good electrical contact
is made between the module and its 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 PCM's 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,
it 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/ICModule 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 recieved, 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, it may cause poor engine performance and possibly a MIL (Service
Engine Soon) with no DTC. |
| • | Knock Sensor (KS) PCM input--The PCM contains integrated
knock sensor diagnostic circuitry. The KS system os 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 recieves 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 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. |
