The Direct Ignition System (DIS) is a distributorless ignition system installed on the 1987-88 2.5L L4 engines (LR8). The DIS system uses individual coils (2), crankshaft sensor, ignition module and Electronic Control Module (ECM) to directly transfer spark to the spark plugs without the use of a distributor assembly. No vacuum or mechanical advances are used.
The DIS system uses a "Waste Spark" method of spark distribution. Each cylinder is paired with its opposing cylinder in the firing order, so that one cylinder fires on the compression stroke and the other on the exhaust stroke. Most of the voltage is used for the compression stroke because little voltage is needed on the exhaust stroke. This dual firing helps reduce exhaust emissions. Timing is not adjustable on these models.
The High Energy Ignition distributor (H.E.I.) with Electronic Spark Timing (EST) combines all ignition components in one unit (2.8L V6). The coil is mounted separately on the (1984-86 2.5L L4).
All spark timing changes in the H.E.I. (EST) distributor are done electronically by and Electronic Control Module (ECM) which monitors information from various engine sensors, computes the desired spark timing and signals the distributor to change the timing accordingly. A back-up spark advance system is incorporated to signal the ignition module in case of (ECM) failure. No vacuum or mechanical advances are used.