IGNITION CONTROL MODULE (ICM)
The ignition control module is mounted to the ignition coil. (Scheme 244) Based on control system inputs, the ECU triggers the ignition coil via the ignition control module. The ECU is able to advance or retard ignition timing by controlling the ignition coil through the ignition control module.
The ICM consists of a solid state ignition circuit, an integrated ignition circuit and an integrated ignition coil that can be removed and serviced separately if necessary.
The ECU provides an input signal to the ICM. The ICM has only two outputs
- Tach signal to the tachometer and diagnostic connector
- High voltage from the coil to the distributor cap
View of Ignition Control Module/Ignition Coil Assembly. Scheme 244
IGNITION CONTROL MODULE (ICM) ELECTRICAL FEED CONNECTIONS
Electrical feed to the ICM is through terminal "A" of Connector No. 1 on the module. (Scheme 245)
Note. Electrical supply only occurs with the ignition switch in the START and RUN position.
Scheme 245
Terminal "B" of Connector No. 1 is grounded at the engine oil dipstick bracket along with the ECU ground wire and Oxygen (O2) sensor ground.
The tachometer output signal wire of the ICM is connected to Pin No. 1 of the "D1" Diagnostic connector. The wire is routed to the diagnostic connector through a short section of the ECU harness, the engine, and the instrument panel harness. This type of routing eliminates any potential electrical interference from occurring in the various ECU circuitry.
Ignition firing signals from ECU terminal "27" are transmitted through terminal "B" of Connector No. 2 on the ICM. the ignition signal from the ECU is received by the ICM in the form of a 5 volt square wave. As the leading edge of the wave contacts the ignition circuitry in the ICM, the ICM charges the coil primary windings.
When coil saturation occurs, the module circuitry opens the primary windings to collapse the magnetic field in the windings. This induces the coil secondary windings which is then transmitted to the spark plug via the coil wire, distributor cap, and rotor.
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
The MAP sensor reacts to absolute pressure in the intake manifold and provides an input signal to the ECU. As the engine load changes, manifold pressure varies, which causes the MAP sensor resistance to change, resulting in a different input voltage to the ECU. The input voltage level supplies the ECU with information relating to ambient barometric pressure during engine start-up or regarding engine load while the engine is running. The ECU calculates this information and adjusts the air-fuel mixture accordingly.
The MAP sensor is mounted under the hood on the firewall and is connected to the throttle body with a vacuum hose. (Scheme 246)
Scheme 246
COOLANT TEMPERATURE SENSOR (CTS)
The coolant temperature sensor is installed in the engine water jacket on the left side of the engine. (Scheme 247) It provides an input voltage to the ECU. As coolant temperatures vary, the Coolant Temperature Sensor resistance changes, resulting in a different input voltage to the ECU. The ECU calculates this information and adjusts the following
- Adjust fuel injector pulse width. Colder coolant temperatures will result in longer injector pulse width and richer air-fuel mixtures.
- Compensate for fuel condensation in the intake manifold.
- Control engine warm-up idle speed.
- Increase ignition advance when the coolant is cold.
- Energize the EGR valve solenoid, thus preventing the flow of vacuum to the EGR valve.
Scheme 247
MANIFOLD AIR TEMPERATURE (MAT) SENSOR
The Manifold Air Temperature (MAT) sensor is installed in the intake manifold with the sensor element extending into the air-fuel stream (Scheme 248) The MAT sensor provides an input voltage to the ECU. As the temperature of the air-fuel stream in the manifold varies, resistance changes, resulting in a different input voltage to the ECU.
Scheme 248
ENGINE SPEED SENSOR (CRANKSHAFT POSITION SENSOR - CPS)
The engine speed sensor is attached to the flywheel cover housing and provides an input signal to the ECU relating to crankshaft speed, angle, and position. (Scheme 249) The ECU converts crankshaft speed input into engine RPM and converts crankshaft angle to piston position. The engine speed sensor senses TDC, BDC, and engine speed by detecting the flywheel teeth as they pass by the sensor during engine operation. The engine speed sensor is non-adjustable.
The flywheel has three trigger notches, 120° apart. (Scheme 249) There are 20 small teeth between each trigger notch. Each large trigger notch is located 12 small teeth before each Top Dead Center (TDC) position of the corresponding pistons.
Scheme 249
When a small tooth and notch pass the magnet core in the sensor, the concentration, followed by the collapse of the magnetic flux induces a small voltage spike to the sensor pickup coil winding. These small voltage spikes enable the ECU to count the teeth as they pass the sensor. When a large trigger tooth and notch pass the magnetic core in the sensor, the increased concentration, and then collapse of the magnetic flux induces a higher voltage spike into the sensor pickup coil winding. (Scheme 250)
Scheme 250
The higher voltage spike is an indication to the ECU that a piston will reach its TDC position, 12 teeth later. (Scheme 251) The ignition timing for the particular cylinder is either advanced or retarded as necessary by the ECU according to sensor inputs.
Scheme 251
SYNC PULSE SIGNAL GENERATOR (STATOR)
The sync pulse signal generator is located in the distributor and works in conjunction with the engine speed sensor to provide the ECU with input to establish and maintain correct injector firing order. (Scheme 252) A pulse ring mounted to the distributor shaft references the position of pistons one and six as it rotates through the sync pulse signal generator's magnetic field.
Scheme 252
The pulse ring rotates through the sync pulse signal generator for l80°. When the leading edge of the pulse enters the sync pulse signal generator, the magnetic field becomes weaker. This indicates the position of piston number one to the ECU. When the trailing edge of the pulse ring leaves the sync pulse signal generator, the magnetic field becomes stronger. This indicates the position of piston number six.
The sync pulse signal input and engine speed sensor input allow the ECU to establish the necessary reference point to synchronize the fuel injection.
Scheme 253
KNOCK SENSOR
The knock sensor is located on the lower left side of the engine block just above the oil pan. (Scheme 254) The knock sensor provides an input to the ECU, indicating detonation (knock) during engine operation. When knock occurs, the ECU retards the ignition advance to eliminate the knock at the appropriate cylinder(s).
Scheme 254
IGNITION SYSTEM PRECAUTIONS
When disconnecting wire from spark plug or distributor cap, twist rubber boot slightly to loosen. Grasp boot (not wire) and pull with steady, even force.
When separating control unit connectors, pull with firm, straight force. DO NOT pry apart with screwdriver. When connecting, press together firmly to overcome hydraulic pressure of silicone grease.
If connector locking tabs weaken or break, press together firmly and bind with electrical tape or a harness tie strap to assure good connection.
SPARK PLUG CHECK
Faulty or fouled plugs may perform well at idle speed, but at higher engine speeds, they frequently fail. Faulty plug can exhibit the following symptomes
- Poor fuel economy.
- Power loss.
- Decreased engine speed.
- Hard starting.
- Generally poor performance.
Spark plugs also malfunction due to carbon fouling, excessive electrode air gap, or broken insulators.