Ignition System - c3i Buick Electra Estate Wagon

DESCRIPTION

The Computer Controlled Coil Ignition System (C3I) eliminates the need for a mechanical distributor. The C3I system works in conjunction with the Computer Command Control System (CCC) to maintain vehicle performance and lower emissions. An Electronic Spark Timing System (EST) is used on C3I equipped vehicles.

The C3I system consists of an electronic control module (ECM), ignition module, and crankshaft and camshaft position sensors. The primary function of the ECM is to control spark advance. Timing is controlled by the ECM from the following inputs: Crankshaft position, engine speed, engine temperature, and amount of air entering 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 C3I system, each cylinder is paired with the cylinder that is opposite in the firing order. Cylinders 1-4, 5-2, and 3-6 are paired. The spark occurs simultaneously in the cylinder coming up on compression and in the cylinder coming up on exhaust. The process is repeated when the cylinders reverse roles. Each cylinder pair is fired by its own ignition coil. Ignition coils are mounted on the ignition module.

Ignition timing can also be modified by the Electronic Spark Control System (ESC). This system retards ignition timing to reduce spark knock. The ESC system consists of an ESC module and a knock sensor.

Buick C3I System Components. Scheme 1

Crankshaft Position Sensor

The crankshaft position sensor is a Hall Effect switch which sends a signal to the ignition module and the ECM. The signal gives the TDC position of each piston. The ignition module uses the signal to trigger each ignition coil at the correct time.

Camshaft Position Sensor

A Hall Effect camshaft sensor provides the ECM with the exact position of the valves. This signal is used by the ECM to properly time the fuel injection and start the spark plug firing sequence.

Power Circuit

A 10 amp fuse provides power for the ignition coils. A 7.5 amp ECM fuse provides a low current source for sensors and internal circuitry.

Crankshaft Signal

Terminal "C" provides the ECM with RPM and crankshaft position from a Hall Effect switch. (Scheme 5) A plate with 3 vanes is mounted on the harmonic balancer. The vanes pass through slots in the crankshaft sensor. As the vanes pass through the slots, a signal is sent to ignition module and from there to the ECM.

The signal from the switch is either high or low and is used to trigger the ignition module for proper engine timing. Both camshaft and crankshaft sensor signals must be seen by the ignition module for a signal to be sent to the ECM.

By-Pass Mode

During cranking, or whenever ECM fails, the C3I system goes into by-pass mode. In by-pass mode, timing is controlled by ignition module and is preset at 10° BTDC.

At about 400 RPM, ECM applies 5 volts to terminal "B" to switch timing control from ignition module to ECM. An open or grounded by-pass circuit will set a Trouble Code 42.

EST Signal

Terminal "A" triggers the HEI module. The ECM does not know the exact timing, but it will advance or retard timing from the point when it receives a reference signal. Timing is determined by crankshaft sensor and is not adjustable.

Camshaft Signal

The ECM uses Terminal "E" to determine when No. 1 cylinder is on compression stroke. This signal starts the firing sequence and times fuel injector opening. Loss of camshaft signal will set a Trouble Code 41 if engine is running. Loss of signal during cranking will cause a no-start condition.

Coolant & Mass Air Flow (MAF) Sensors

The ECM uses signals from coolant and MAF sensors to calculate timing as follows

1. Cold Engine - More spark advance.
2. Engine Under Minimum Load - More spark advance.
3. Hot Engine - Less spark advance.
4. Engine Under Heavy Load - Less spark advance.

ELECTRONIC SPARK CONTROL SYSTEM OPERATION

ESC knock sensor detects engine spark knock. The ESC module receives sensor information and signals the ECM to retard timing. ECM normally receives a 8-10 volt signal from the ESC module. When spark knock occurs, module turns off the circuit to the ECM. Terminal "B7" goes to 0 volts and the ECM retards timing. Sensor is mounted at rear of intake manifold. The ESC module is mounted on right side fender.

Scheme 2

1. Remove No. 1 spark plug. Bring No. 1 cylinder to TDC on compression stroke. Mark harmonic balancer and rotate engine to 25° ATDC. Remove plug wires from coil assembly.
2. Using removal tool (J-28742-A) or equivalent, remove terminal "B" of sensor 3-way connector on module side. Install jumper wire into terminal "B". Connect wire that was removed to jumper wire. (Scheme 2) (Scheme 2): Adjusting Camshaft Sensor
3. Connect voltmeter between jumper wire and ground. Turn ignition to "ON". Rotate camshaft sensor counterclockwise until sensor switch just closes. This indicated by the voltage reading going from 5-12 volts to 0-2 volts.
4. Low voltage indicates switch is closed. Tighten retaining bolt. Install spark plug and wires. Remove jumper wire and install wire in terminal "B".

TROUBLE SHOOTING

Note. See the TROUBLE SHOOTING - BASIC PROCEDURES article in the GENERAL TROUBLE SHOOTING section.

TESTING & DIAGNOSIS

Note. Additional information concerning testing and diagnosis may be found in the appropriate TESTS W/CODES article in the ENGINE PERFORMANCE section. Refer to the following list.

1. For 1.8L, see: «1.8L/2.5L TBI TESTS W/CODES»(ref-94851) .
2. For 2.5L, see: «1.8L/2.5L TBI TESTS W/CODES»(ref-94851) .
3. For 3.0L, see: «3.0L/3.8L PFI TESTS W/CODES»(/buick/electra-estate-wagon/1985-1985/remont/testing-diagnostics/#30l38l-pfi-tests-wcodes) .
4. For 3.8L, see: «3.0L/3.8L PFI TESTS W/CODES»(/buick/electra-estate-wagon/1985-1985/remont/testing-diagnostics/#30l38l-pfi-tests-wcodes) .

Ignition System Diagnosis - Chart No. 1 (3.8L Only). Scheme 3

Ignition System Diagnosis - Chart No. 2 (3.8L Turbo Only). Scheme 4

ELECTRONIC SPARK CONTROL SYSTEM

1. Connect tachometer to terminal "D" of ignition module. Place transmission in "P" or "N". Start engine. Run at approximately 1800 RPM. Tap engine block in area of knock sensor and check for RPM drop.
2. If RPM drops, system is OK. If no RPM drop, unplug the ESC module and check for RPM drop. If there is no RPM drop, go to step 6.
3. If RPM drops, run engine at 2000 RPM and check voltage between pins "E" and "D" with digital voltmeter. There should be over 80 millivolts (.080 volts) at 2000 RPM. (Scheme 5)
4. If voltage correct, check for faulty ESC connection or ESC module. If voltage not correct, check for open in ground circuit. Ground is BLK/WHT wire at terminal "D" of ESC module.
5. If ground circuit is OK, check for faulty connection from knock sensor to module. If circuit is OK, replace knock sensor.
6. If there was no RPM drop when ESC module was disconnected in step 2), check engine light. If light is off, turn engine off and turn ignition "ON". Check if there is 2 volts present at ESC harness terminal "C".
7. If there is less than 2 volts, replace ECM. If over 2 volts, correct short on YEL/BLK wire from ESC terminal "C" to ECM terminal "B7".
8. If engine light was on in step 6, plug in ESC module and run engine at 1500 RPM. Check timing. Unplug knock sensor and check for timing change. If timing changed, replace knock sensor.
9. If timing did not change in step 8, remove terminal "E" from ESC module connector with engine at 1500 RPM. Check timing. If no change, check for faulty ESC connection or module.
10. If timing changed, knock sensor-to-ESC module wire may be routed too close to ignition wires and picking up false knock signals.

Removal & Installation

Disconnect negative battery cable. Unplug 14-way connector at ignition module. Disconnect spark plug wires. Remove ignition module from bracket. Remove 6 coil-to-ignition module screws. Unplug connectors between ignition coil and module and remove module. To install, reverse removal procedure.

Removal

Disconnect negative battery cable. Unplug 3-way connector. Raise and support vehicle. Position harmonic balancer so that slot in disc is lined up with sensor. Loosen retaining bolt. Slide sensor through notch in sensor housing.

Installation

Install sensor in housing. Rotate harmonic balancer so that disc is positioned in sensor. Adjust sensor so that there is an equal distance on each side of disc. There should be approximately .030" (.76 mm) between disc and sensor. Tighten retaining bolt. Continue installation in reverse of removal procedure.

Disconnect negative battery cable. Unplug module 14-way connector. Disconnect spark plug wires from module. Remove ignition module bracket assembly. Unplug sensor 3-way connector. Remove 2 sensor retaining screws and lift off sensor. To install, reverse removal procedure.

Remove camshaft position sensor as previously described. Note position of slot in rotating vane. Remove bolt securing drive assembly in engine. Remove drive assembly.

Install camshaft assembly with slot in vane. Install bolt and washer. Install camshaft sensor as previously described. Adjust camshaft sensor timing.

OVERHAUL

Overhaul information is not available.

Buick C3I System Wiring Diagram. Scheme 5

Electronic Spark Control System Wiring Diagram. Scheme 6

See also:
• TROUBLE SHOOTING - BASIC PROCEDURES
• 3.0L/3.8L PFI TESTS W/CODES