DESCRIPTION
Computer controlled coil (C(3)I) ignition system eliminates the need for a mechanical distributor. The C(3)I ignition system consists of a coil pack, an ignition module, camshaft and crankshaft position sensors or a combination sensor, the necessary wiring, as well as the Electronic Spark Timing (EST) portion of the Electronic Control Module (ECM).
This system utilizes the EST signal from the ECM to control spark timing. Ignition timing is controlled by the ECM by using information from the following inputs: crankshaft position, camshaft position, engine RPM, engine temperature, induction air temperature, throttle position, knock retard (ESC), vehicle speed, gear position, and the amount of air entering the intake manifold.
Input from the sensors is used by the ignition module to determine correct spark plug firing sequence. The ignition module then selects and sequentially triggers each of 3 interconnected coils to fire spark plugs at the proper crankshaft position.
In the C(3)I ignition system, each cylinder is paired with the cylinder that is opposite in the firing order. Cylinders No. 1-4, 5-2, and 3-6 are paired. The spark occurs simultaneously in the cylinder coming up on the compression stroke and in the cylinder coming up on the exhaust stroke. The process is repeated when the cylinders reverse roles. Each cylinder pair is fired by its own ignition coil.
C(3)I IGNITION MODULE
The ignition module monitors input signals from several engine sensors. It then passes this information to the ECM so that correct spark and fuel injector timing can be maintained. Below 400 RPM, the module controls spark advance by triggering each of the 3 coils at a pre-determined interval based on engine speed only. Above 400 RPM, the ECM controls the EST and compensates for all driving conditions. The ignition module is located directly below coil pack, on top of engine.
ELECTRONIC CONTROL MODULE (ECM)
The ECM maintains proper spark and fuel injection timing for all driving conditions. The ECM monitors input signals from the following components to control Electronic Spark Timing (EST)
- C(3)I Ignition Module
- Coolant Temperature Sensor (CTS)
- Manifold Air Temperature (MAT) Sensor
- Mass Airflow Sensor
- Park/Neutral Switch
- ESC Module
- Throttle Position Sensor (TPS)
- Vehicle Speed Sensor (VSS)
Under 400 RPM, the ECM will start injector timing as soon as the C(3)I ignition module receives a cam signal, synchronizes spark timing, and controls fuel injection timing.
The C(3)I ignition module controls spark timing during this period. Over 400 RPM, the ECM controls EST. It also changes fuel injection timing to a sequential mode (provided a camshaft signal is received).
ELECTRONIC SPARK CONTROL (ESC)
The ESC system consists of a knock (detonation) sensor and the ESC module. The ECM monitors ESC signal to determine when engine detonation occurs. When the knock sensor detects detonation, the ESC module signals the ECM. The ECM, in turn, retards EST to reduce detonation. The knock sensor is mounted at rear of intake manifold. The ESC module is mounted on right side fender.
ELECTRONIC SPARK TIMING (EST)
The EST system uses the same EST-to-ECM circuits that distributor type ignition systems use. Operation of each circuit is described in the following paragraphs.
Reference Signal
The reference signal provides the ECM with RPM and crankshaft position information from the C(3)I ignition module. A loss of reference signal will prevent engine from running.
By-Pass Signal
At about 400 RPM, the ECM applies 5 volts to this circuit to switch spark timing control from the C(3)I ignition module to the ECM. An open or grounded by-pass circuit will operate engine in a back-up ignition timing mode. Code 42 (E042 on some models) will be set.
EST Signal
The C(3)I ignition module sends a reference signal to the ECM when the engine is cranking. If the engine is under 400 RPM, the ECM applies 5 volts to the by-pass line to switch spark timing to ECM control. An open or grounded EST circuit will stall the engine. The engine can be restarted but will operate in a back-up ignition timing mode. Code 42 (E042 on some models) will be set.
Camshaft Signal
The ECM uses this signal to determine when cylinder number one is on its compression stroke. This signal starts the firing sequence and times fuel injector opening. If camshaft signal is lost while the engine is running, the fuel injection system will shift to a simultaneous injection mode, thus allowing the engine to continue to run. The engine can be restarted but will continue to run in the simultaneous mode as long as fault is present. Code 41 (E041 on some models) will be set.
Type I
On type I ignition coils, 3 twin tower coils are combined into a single coil pack. Coil pack is mounted directly over the C(3)I ignition module. Each coil provides the spark for 2 simultaneously paired spark plugs. All 3 coils must be replaced as a unit.
Type II
On type II ignition coils, 3 separate coils are independently mounted over the C(3)I ignition module. Each coil provides the spark for 2 simultaneously paired spark plugs. Each coil can be replaced separately.
Type I & Type II Ignition Coils. Scheme 1
CRANKSHAFT POSITION SENSOR
The crankshaft position sensor is a Hall Effect switch which sends a signal to the ignition module. The signal gives the TDC position of each piston. The ignition module uses the signal to trigger each ignition coil at the correct time.The crankshaft sensor is mounted near the harmonic balancer.
3.8L C(3)I Ignition Sensors. Scheme 2
CAMSHAFT POSITION SENSOR
A Hall Effect camshaft position sensor provides the ECM with the exact position of the valves. The signal created by the camshaft position sensor is used by the ECM to properly time the fuel injection and start the spark plug firing sequence.
Camshaft position sensor is located on top of engine front
cover, above water pump. (Scheme 3)
CRANKSHAFT SENSOR
Note. Information not available from manufacturer.
TROUBLE SHOOTING
Note. See the TROUBLE SHOOTING - BASIC PROCEDURES article in the GENERAL TROUBLE SHOOTING section.
TESTING
The C(3)I ignition system is an integral part of the engine's computerized engine control system. Refer to 3800 ECM TESTS/CODES article in the COMPUTERIZED ENGINE CONTROLS section for appropriate testing and diagnosis information.
If engine cranks but will not run or if it stalls, CHART A-3 must be used to determine if failure is in the C(3)I ignition system or fuel injection system.
If either Code 41 or Code 42 (E041 or E042 on some models) is set, use appropriate chart for proper diagnosis. If symptom is an engine miss and the C(3)I ignition system is suspected, CHART C-4F must be used.
Removal & Installation
Disconnect negative battery cable. Unplug 14-way connector at ignition module. Disconnect spark plug wires from coil pack. Remove ignition module from bracket. Remove 6 coil-to-ignition module screws. Unplug connectors between ignition coil and module. Remove module. To install, reverse removal procedure.
Removal
- Disconnect crankshaft sensor harness connector.
- Position harmonic balancer so that window in interrupter ring is lined up with sensor. Loosen sensor retaining bolt until sensor is free to slide in pedestal. Remove pedestal mounting bolts. Carefully remove sensor and pedestal as an assembly.
Installation
- Loosen bolt on pedestal until sensor is free to slide in pedestal. Verify that window in interrupter ring is properly positioned. Install sensor and pedestal as an assembly. Install and tighten pedestal mounting bolts.
- Rotate harmonic balancer until interrupter ring fills sensor slot and edge of window is aligned with edge of deflector on pedestal. Insert Crankshaft Position Sensor Adjuster (J-36179) into gap between sensor and each side of interrupter ring.
- If gauge will not slide past sensor on either side of ring, sensor is out of adjustment or interrupter ring is bent. Check clearance at 3 positions around outer interrupter ring (about 120 degrees apart). See ADJUSTMENTS in this article.
Disconnect negative battery cable. Remove camshaft sensor attaching bolt. Disconnect wiring harness and remove sensor. To install, reverse removal procedure.
C(3)I Ignition Sensors. Scheme 3
Disconnect negative battery cable. Remove spark plug wires from coil pack. Remove screws securing coil to ignition module. Tilt coil assembly back. Disconnect module connectors and remove coil pack. To install, reverse removal procedure.
Disconnect negative battery cable. Remove spark plug wires from coil. Remove nuts and ignition coil. To install, reverse removal procedure.
See also:
• TROUBLE SHOOTING - BASIC PROCEDURES