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 in the engine block, behind the timing cover, near the camshaft sprocket. The CMP sensor is a variable reluctance sensor. The magnetic field of the sensor is altered by a camshaft mounted
reluctor wheel. This provides the PCM with 1 digital output pulse per revolution of the camshaft.
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 P1361 will be set, and the ignition system will operate in Bypass Mode. |
