DESCRIPTION
The Direct Ignition System (DIS) eliminates the need for the conventional distributor. The DIS ignition system consists of 2 or 3 separate ignition coils, a DIS ignition module, a crankshaft position sensor, wiring harness and 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, using information from the following inputs: crankshaft position, engine RPM, engine temperature, engine load (manifold pressure or vacuum), air temperature and atmospheric pressure.
In the direct ignition system, each cylinder is paired with the cylinder opposite it in the firing order. On 2.8L engines, cylinders No. 1-4, 3-6 and 2-5 are paired together.
The spark occurs simultaneously in the cylinder coming up on the compression stroke and in the cylinder coming down on the exhaust stroke. The process is repeated when the cylinders reverse roles. Each cylinder pair is fired by its own ignition coil.
IGNITION MODULE
The DIS ignition module monitors crankshaft position sensor signals and based on these signals, sends a reference signal to the ECM so that correct spark and fuel injector control can be maintained during all driving conditions.
During cranking the ignition module monitors crankshaft sensor synchronization pulse to begin ignition firing sequence. Below 400 RPM, the ignition coil module controls spark by a predetermined interval based on engine speed alone. Above 400 RPM, the ECM controls the EST and compensates for all driving conditions. The ignition module is incorporated into the coil pack. (Scheme 1)
ELECTRONIC SPARK TIMING (EST)
The EST system uses the same EST-to-ECM wiring circuits as distributor type ignition systems use. Operation of each circuit is described in the following paragraphs.
IGNITION REFERENCE SIGNAL
The crankshaft position sensor sends a signal to the DIS ignition module which results in a reference signal being sent to the ECM. The ECM uses this signal to calculate the crankshaft position, engine RPM and injector pulse width.
REFERENCE GROUND
The EST system is grounded through the DIS ignition module to ensure that the ground circuit does not have excessive amount of voltage drop between the ignition module and the ECM. An excessive voltage drop in the system could affect engine performance.
BY-PASS SIGNAL
At about 400 RPM, the ECM applies 5 volts to this circuit to switch spark timing control from the DIS module to the ECM. On open or grounded by-pass circuit will cause the engine control system to operate in an ignition timing back-up mode. A code 42 will be set.
EST SIGNAL
The DIS ignition module sends a reference signal to the ECM when engine is cranking. If the engine RPM is under 400, the DIS ignition module controls the ignition timing. If engine RPM is above 400, the ECM applies a 5 volt signal to the by-pass circuit to switch spark timing control to the ECM.
An open or grounded EST circuit will result in engine operating in an ignition timing back-up mode and the "SERVICE ENGINE SOON" light will illuminate. If the EST fault is present the next time the engine is started, code 42 will be set.
IGNITION COILS
Separate ignition coils are mounted over the DIS ignition module. Each coil provides the spark for 2 simultaneously paired spark plugs. Each coil can be replaced separately.
CRANKSHAFT POSITION SENSOR
The crankshaft position sensor is mounted on the bottom of the DIS ignition module or near to the ignition module. (Scheme 1)The sensor protrudes into the engine block and is mounted within.050" (1.3 mm) of the crankshaft reluctor. Sensor position is not adjustable.
The reluctor is a special piece of metal cast with the crankshaft. It has 7 slots machined into it, 6 of which are equally spaced (about 60 degrees apart). A seventh slot is spaced about 10 degrees from one of the other slots and generates a synchronization pulse signal. As reluctor rotates, the slots change the magnetic field to the sensor, creating an induced voltage.
TROUBLE SHOOTING
Note. See the TROUBLE SHOOTING - BASIC PROCEDURES article in the GENERAL TROUBLE SHOOTING section.
TESTING
The ignition system is an integral part of the engine's computerized engine control (CEC) system. For testing and diagnosis information, see the 2.8L VINS [S,9] PFI CEC TESTS W/CODES article in the ENGINE PERFORMANCE section.
EST PERFORMANCE CHECK
- The ECM will set timing at a specified value when diagnostic test terminal of the ALDL connector is grounded. To check the EST operation, perform the following steps
- Start and run engine at 1500 RPM with the ALDL diagnostic test terminal NOT grounded. Ground test terminal. When ALDL test terminal is grounded there should be a noticeable change in engine RPM. When a fault in the EST system takes place, a code 42 should be set.
- If code 42 is set, use appropriate chart for diagnosis. If symptom is engine miss and the direct ignition system is suspect, use CHART C-4D DIS MISFIRE in the «2.8L VINS [S,9] PFI CEC TESTS W/CODES»(ref-94880) article in the ENGINE PERFORMANCE section for proper diagnosis.
2.8L Direct Ignition System Components. Scheme 1
Removal & Installation
- Disconnect negative battery cable. Unplug connectors at ignition module. Disconnect spark plug wires from coil pack. Remove ignition module from engine block. Remove coils and assembly plate. To install, reverse removal procedures.
Note. If spark plug boots adhere to spark plugs, use Boot Remover (J-36011). Twist first and then pull upward. Boots must be in place on housing prior to ignition system assembly installation or damage may result.
Disconnect sensor harness at DIS ignition module. Remove bolt and sensor from engine block. (Scheme 1) Inspect crankshaft sensor "O" ring for wear, cracks or other damage. Replace if necessary. Lubricate new "O" rings with engine oil before installing. To install, reverse removal procedure.
Disconnect negative battery cable. Remove spark plug wires from coils. Remove nuts or screws from ignition coils. Remove coils. To install, reverse removal procedure.
OVERHAUL
Overhaul information is not available.
See also:
• TROUBLE SHOOTING - BASIC PROCEDURES