Ignition System: Description and Operation

IGNITION SYSTEM
The system's three main components are the coil pack, crankshaft position sensor, and camshaft position sensor.

Basic ignition timing is not adjustable. The Powertrain Control Module (PCM) determines spark advance. These engines use a fixed ignition timing system. The distributorless electronic ignition system is referred to as the Direct Ignition System (DIS).

SPARK PLUGS
These engines uses resistor spark plugs. For spark plug identification and specifications.

Remove the spark plugs and examine them for burned electrodes and fouled, cracked or broken porcelain insulators. Keep plugs arranged in the order in which they were removed from the engine. An isolated plug displaying an abnormal condition indicates that a problem exists in the corresponding cylinder.

Checking Spark Plug Electrode Gap:

Spark plugs that have low mileage may be cleaned and reused if not otherwise defective. Refer to the Spark Plug Condition. After cleaning, file the center electrode flat with a small point file or jewelers file. Adjust the gap between the electrodes to the dimensions specified in the chart at the end by bending the ground electrode. Adjust above the attachment weld) with the appropriate tool.

Never apply any force between the electrode or damage to the center electrode assembly will result.

Always tighten spark plugs to the specified torque. Over tightening can cause distortion and damage. Tighten spark plugs to 28 Nm (20 ft. lbs.) torque.

SPARK PLUG CABLES
Spark plug cables are sometimes referred to as secondary ignition wires. The wires transfer electrical current from the coil pack to individual spark plugs at each cylinder. The resistor type, nonmetallic spark plug cables provide suppression of radio frequency emissions from the ignition system.

Check the spark plug cable connections for good contact at the coil and spark plugs. Terminals should be fully seated. The nipples and spark plug covers should be in good condition. Nipples should fit tightly on the coil. Spark plug boot should completely cover the spark plug hole in the cylinder head cover. Install the boot until the terminal snaps over the spark plug. A snap must be felt to ensure the spark plug cable terminal engaged the spark plug.

Loose cable connections will corrode, increase resistance and permit water to enter the coil towers. These conditions can cause ignition malfunction. Plastic clips in various locations protect the cables from damage. when the cables are replaced the clips must be used to prevent damage to the cables, and should be rotated about 30° below the horizontal.

ELECTRONIC IGNITION COILS

Ignition Coil Pack:

The coil pack consists of 2 coils molded together. The coil pack is mounted on the valve cover.

WARNING: THE DIRECT IGNITION SYSTEM GENERATES APPROXIMATELY 40,000 VOLTS. PERSONAL INJURY COULD RESULT FROM CONTACT WITH THIS SYSTEM.

High tension leads route to each cylinder from the coil. The coil fires two spark plugs every power stroke. One plug is the cylinder under compression, the other cylinder fires on the exhaust stroke. Coil number one fires cylinders 1 and 4. Coil number two fires cylinders 2 and 3. The PCM determines which of the coils to charge and fire at the correct time.

The Auto Shutdown (ASD) relay provides battery voltage to the ignition coil. The PCM provides a ground contact (circuit) for energizing the coil. When the PCM breaks the contact, the energy in the coil primary transfers to the secondary causing the spark. The PCM will de-energize the ASD relay if it does not receive the crankshaft position sensor and camshaft position sensor inputs. Refer to Auto Shutdown (ASD) Relay-PCM Output, for relay operation.

AUTOMATIC SHUTDOWN RELAY

Power Distribution Center (PDC):

The ASD relay is located in the PDC. The inside top of the PDC cover has label showing relay and fuse identification.

The Automatic Shutdown (ASD) relay supplies battery voltage to the fuel injectors, electronic ignition coil and the heating elements in the oxygen sensors.

A buss bar in the Power Distribution Center (PDC) supplies voltage to the solenoid side and contact side of the relay. The fuse also protects the power circuit for the fuel pump relay and pump. The fuse is located in the PDC.

The PCM controls the ASD relay by switching the ground path for the solenoid side of the relay on and off. The PCM turns the ground path off when the ignition switch is in the Off position. When the ignition switch is in On or Start, the PCM monitors the Crankshaft and Camshaft Position Sensor signals to determine engine speed and ignition timing (coil dwell). If the PCM does not receive Crankshaft and Camshaft Position Sensor signals when the ignition switch is in the RUN position, it will de-energize the ASD relay.

CRANKSHAFT POSITION SENSOR-PCM INPUT

Crankshaft Position Sensor:

The Crankshaft Position Sensor mounts to the engine block behind the generator, just above the oil filter.

The PCM uses the Crankshaft Position Sensor to calculate the following:
- Engine RPM
- TDC number 1 and 4
- Ignition coil synchronization
- Injector synchronization
- Camshaft-to-crankshaft misalignment (Timing belt skipped 1 tooth or more diagnostic trouble code).

Timing Reference Notches:

The Crankshaft Position (CKP) Sensor is a Hall-effect sensor. The second crankshaft counterweight has two sets of four timing reference notches including a 60 degree signature notch.

The PCM sends approximately 8 volts to the Hall-effect sensor. This voltage is required to operate the Hall-effect chip and the electronics inside the sensor.

A ground for the sensor is provided through the sensor return circuit. The input to the PCM occurs on a 5 volt output reference circuit.

The notches generate pulses from high to low in the Crankshaft Position Sensor output voltage. When a metal portion of the counterweight aligns with the Crankshaft Position Sensor, the sensor output voltage goes low (less than 0.5 volts). When a notch aligns with the sensor, voltage goes high (5.0 volts). As a group of notches pass under the sensor, the output voltage switches from low (metal) to high (notch) then back to low.

If available, an oscilloscope can display the square wave patterns of each voltage pulses. From the width of the output voltage pulses, the PCM calculates engine speed. The width of the pulses represent the amount of time the output voltage stays high before switching back to low. The period of time the sensor output voltage stays high before switching back to low is referred to as pulse width. The faster the engine is operating, the smaller the pulse width on the oscilloscope.

By counting the pulses and referencing the pulse from the 60 degree signature notch, the PCM calculates crankshaft angle (position). In each group of timing reference notches, the first notch represents 69 degrees before top dead center (BTDC). The second notch represents 49 degrees BTDC. The third notch represents 29 degrees. The last notch in each set represents 9 degrees before top dead center (TDC).

The timing reference notches are machined at 200 increments. From the voltage pulse width the PCM tells the difference between the timing reference notches and the 60 degree signature notch. The 60 degree signature notch produces a longer pulse width than the smaller timing reference notches. If the Camshaft Position Sensor input switches from high to low when the 60 degree signature notch passes under the crankshaft position sensor the PCM knows cylinder number one is the next cylinder at TDC.

CAMSHAFT POSITION SENSOR-PCM INPUT

Camshaft Position Sensor (SOHC):

The Camshaft Position Sensor attaches to the rear of the cylinder head. The PCM determines fuel injection synchronization and cylinder identification from inputs provided by the Camshaft Position Sensor and Crankshaft Position Sensor. From the two inputs, the PCM determines crankshaft position.

The PCM sends approximately 8 volts to the hall effect sensor. This voltage is required to operate the hall effect chip and the electronics inside the sensor. A ground for the sensor is provided through the sensor return circuit. The input to the PCM occurs on a 5 volt output reference circuit.

Target Magnet - Typical:

Target Magnet Polarity:

A target magnet attaches to the rear of the camshaft and indexes to the correct position. The target magnet has four different poles arranged in an asymmetrical pattern. As the target magnet rotates, the camshaft position sensor senses the change in polarity. The sensor output switch switches from high (5.0 volts) to low (0.5 volts) as the target magnet rotates. When the north pole of the target magnet passes under the sensor, the output switches high. The sensor output switches low when the south pole of the target magnet passes underneath.

The sensor also acts as a thrust plate to control camshaft endplay.

KNOCK SENSOR
The knock sensor threads into the cylinder block.

When the Knock Sensor detects a knock in one of the cylinders, it sends an input signal to the PCM. In response, the PCM retards ignition timing for all cylinders by a scheduled amount.

Knock sensors contain a piezoelectric material which constantly vibrates and sends an input voltage (signal) to the PCM while the engine operates. As the intensity of the crystal's vibration increases, the knock sensor output voltage also increases.

NOTE: Over or under tightening affects knock sensor performance, possibly causing improper spark control.

IGNITION SWITCH
In the RUN position, the ignition switch connects power from the Power Distribution Center (PDC) to a fuse in the fuse block, back to a bus bar in the PDC. The bus bar feeds circuits for the Powertrain Control Module (PCM), Proportional purge solenoid, EGR solenoid, and ABS system. The bus bar in the PDC feeds the coil side of the radiator fan relay, A/C compressor clutch relay, and the fuel pump relay. It also feeds the Airbag Control Module (ACM)

LOCK KEY CYLINDER
The lock cylinder is inserted in the end of the housing opposite the ignition switch.

Ignition Lock Cylinder Detents:

The ignition key rotates the cylinder to 5 different detents:
- Accessory
- Off (lock)
- Unlock
- On/Run Start

IGNITION INTERLOCK
All vehicles equipped with automatic transaxies have an interlock system. The system prevents shifting the vehicle out of Park unless the ignition lock cylinder is in the Off, Run or Start position. In addition, the operator cannot rotate the key to the lock position unless the shifter is in the park position. On vehicles equipped with floor shift refer to the - Transaxle for Automatic Transmission Shifter/Ignition Interlock.