DESCRIPTION
The Direct Ignition System (DIS) eliminates the need for a mechanical distributor. The DIS ignition system consists of 2 or 3 separate ignition coils, a DIS ignition module, a crankshaft position sensor, and 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, engine RPM, engine temperature, engine load (manifold pressure or vacuum), and atmospheric (barometric) pressure.
In the direct ignition system, each cylinder is paired with the cylinder that is opposite in the firing order. On the 2.0L and 2.5L engines, cylinders No. 1-4 and 2-3 are paired. On the 2.8L engine, cylinders No. 1-4, 3-6, and 2-5 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.
DIS 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.
While cranking, the ignition module monitors crankshaft sensor synchronization pulse to begin ignition firing sequence. Below 400 RPM, the ignition module controls spark advance by triggering each of the 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 side of engine. (Scheme 16)
EST SYSTEM OPERATION
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.
DIS REFERENCE SIGNAL
The crankshaft position sensor sends a signal to DIS ignition module which results in a reference pulse being sent to the ECM. The ECM uses this signal to calculate crankshaft position, engine RPM, and injector pulse width.
REFERENCE GROUND
The EST system is grounded through the DIS ignition module to ensure that ground circuit does not have an excessive voltage drop between ignition module and the ECM. An excessive voltage drop in system could affect engine performance.
2.0L Direct Ignition System (DIS) Components. Scheme 16
BY-PASS SIGNAL
At about 400 RPM, the ECM applies 5 volts to this circuit to switch spark timing control from the DIS ignition module to the ECM. An open or grounded by-pass circuit will operate engine in a back-up ignition timing mode. Code 42 will be set.
EST SIGNAL
The DIS ignition module sends a reference signal to the ECM when the engine is cranking. If the engine is under 400 RPM, The DIS ignition module controls ignition timing. When engine speeds exceeds 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 result in engine operating in a back-up ignition timing mode and the "SERVICE ENGINE SOON" warning light will come on. If EST fault is present the next time 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 OPERATION
The crankshaft position sensor is either mounted on the bottom of the DIS ignition module or next to the ignition module. (Scheme 16), (Scheme 17) and (Scheme 18). The sensor protrudes into the engine block, within 0.05" (1.3 mm) of crankshaft reluctor. Sensor position is not adjustable.
The reluctor is a special wheel cast into the crankshaft with 7 slots machined into it, 6 of which are equally spaced (about 60 degrees apart). A seventh slot is spaced 10 degrees from one of the other slots and serves to generate a synchronization pulse signal. As reluctor rotates, the slots change the magnetic field to sensor, creating an induced voltage.
2.5L Direct Ignition System (DIS) Components. Scheme 17
TROUBLE SHOOTING
Note. See the TROUBLE SHOOTING - BASIC PROCEDURES article in the GENERAL TROUBLE SHOOTING section.
TESTING & DIAGNOSIS INFORMATION
The direct ignition system is an integral part of the engine's Computer Command Control (CCC) system. See the appropriate TESTS W/ CODES article in the COMPUTER ENG CONTROL or ENGINE PERFORMANCE sections under the ENGINE PERFORMANCE category. Refer to the following menu
If engine cranks but will not run or if it stalls, CHART A-3 must be used to determine if failure is in the direct ignition system or fuel injection system. See the appropriate TESTS W/ CODES article in the COMPUTER ENG CONTROL or ENGINE PERFORMANCE sections under the ENGINE PERFORMANCE category. Refer to the following menu
- «2.0L VIN [1] TBI TESTS W/CODES»(ref-94861) - 2.0L, VIN 1
- «2.0L VIN [K] / 2.5L VINS [R & U] TESTS W/CODES»(ref-94862) - 2.5L, VIN U
- «2.8L PFI TESTS W/CODES»(ref-94863) - 2.8L, VINS S, W & 9
EST PERFORMANCE CHECK
The ECM will set timing at a specified value when diagnostic test terminal of ALDL connector is grounded. To check EST operation, perform the following steps
1) Start and run engine at 1500 RPM with ALDL diagnostic test terminal NOT grounded, and then with terminal grounded. If EST is operating properly, there should be a noticeable change in engine RPM. A fault in the EST system will set Code 41.
2) If Code 42 is set, use appropriate chart for diagnosis. If symptom is an engine miss and the direct ignition system is suspected, use CHART C-4D DIS MISFIRE for proper diagnosis. See the appropriate TESTS W/ CODES article in the COMPUTER ENG CONTROL or ENGINE PERFORMANCE sections under the ENGINE PERFORMANCE category. Refer to the following menu
- 2.0L, VIN 1, see: «2.0L VIN [1] TBI TESTS W/CODES»(ref-94861)
- 2.5L, VIN U, see: «2.0L VIN [K] / 2.5L VINS [R & U] TESTS W/CODES»(ref-94862)
- 2.8L, VINS S, W & 9 see: «2.8L PFI TESTS W/CODES»(ref-94863)
Note. Code 12 is used during diagnostic test procedure to check the diagnostic and code display ability of the ECM. This code indicates that ECM is not receiving DIS reference signal. Signal occurs with ignition switch in "ON" position and the engine not running.
DIS IGNITION MODULE R & I
- 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.
- On 2.5L engine, inspect crankshaft sensor "O" ring for wear, cracks, or other damage. (Scheme 17) Replace if necessary. Lubricate new "O" ring with engine oil before installing. To install, reverse removal procedure.
CRANKSHAFT POSITION SENSOR R & I - 2.0L & 2.8L
Disconnect sensor harness at DIS ignition module. Remove bolt and sensor from engine block. (Scheme 18) Inspect crankshaft sensor "O" ring for wear, cracks, or other damage. Replace if necessary. Lubricate new "O" ring with engine oil before installing. To install, reverse removal procedure.
CRANKSHAFT POSITION SENSOR R & I - 2.5L
Remove DIS ignition module. Remove crankshaft sensor screws and pull sensor away from DIS ignition module. Inspect "O" ring before installing DIS ignition module. Replace if necessary. To install, reverse removal procedure.
IGNITION COIL R & I
Disconnect negative battery cable. Remove spark plug wires from coil. Remove nuts or screws and ignition coil. To install, reverse removal procedure.
2.8L Direct Ignition System (DIS) Components. Scheme 18
See also:
• TROUBLE SHOOTING - BASIC PROCEDURES