General Motors uses two basic ignition systems on these vehicles. A high energy distributor type system or a high energy distributorless type system. The High Energy Ignition (HEI) system is virtually maintenance free, since it is electronic and, therefore, uses no breaker points. The only required service for the HEI distributor is to check the distributor cap and rotor for cracks, carbon tracking, and corrosion every 30,000 miles (48,300 km).
On distributorless systems, even less maintenance is required. Since there is no distributor, there is no cap or rotor to wear out. The only normal maintenance required on these systems will be the spark plug and wires. Diagnosis of no start conditions may require testing the ignition module or coil assemblies. These items are not much different than the ignition module or coil used on HEI systems.
The distributorless ignition systems used by General Motors goes by two names, either DIS or C 3 I. DIS simple stands for Distributorless Ignition System while C 3 I stands for Computer Controlled Coil Ignition. Both of these systems function the same way; by connecting a coil pack to a pair of spark plugs and firing the proper coil each time the a specific plug should spark, instead of using a distributor cap and rotor.
The distributorless ignition system is far better than previous system. It allows for more accurate spark control and a higher spark output. This is important at the high rpm& generated by newer engines.
HIGH ENERGY IGNITION (HEI) SYSTEM
See Figure 1
The General Motors HEI system is a pulse-triggered, transistor-controlled, inductive discharge ignition system. The entire HEI system is contained within the distributor cap.
The distributor, contains the ignition coil, the electronic control module, and the magnetic pick-up assembly contains a permanent magnet, a pole piece with internal teeth, and a pick-up coil (not to be confused with the ignition coil).
For 1982 and later an HEI distributor with Electronic Spark Timing (EST) is used (for more information on EST, refer to Driveability & Emissions Controls ).
All spark timing changes in the 1982 and later distributors are done electronically by the Ignition Control Module (ICM) which monitors information from various engine sensors, computes the desired spark timing and then signals the distributor to change the timing accordingly. No vacuum or mechanical advance systems are used whatsoever.
In the HEI system, as in other electronic ignition systems, the breaker points have been replaced with an electronic switch, (a transistor), which is located within the control module. This switching transistor performs the same function the points did in a conventional ignition system; it simply turns coil primary current on and off at the correct time. Essentially then, electronic and conventional ignition systems operate on the same principle.
The module which houses the switching transistor is controlled (turned on and off) by a magnetically generated impulse induced in the pick-up coil. When the teeth of the rotating timer align with the teeth of the pole piece, the induced voltage in the pick-up coil signals the electronic module to open the coil primary circuit. The primary current then decreases, and a high voltage is induced in the ignition coil secondary windings which is then directed through the rotor and spark plug wires to fire the spark plugs.
In essence then, the pick-up coil module system simply replaces the conventional breaker points and condenser. The condenser found within the distributor is for radio suppression purposes only and has nothing to do with the ignition process. The module automatically controls the dwell period, increasing it with increasing engine speed. Since dwell is automatically controlled, it cannot be adjusted. The module itself is non-adjustable and non-repairable and must be replaced if found defective.
DISTRIBUTORLESS IGNITION SYSTEMS
See Figures 2, 3, 4 and 5
Starting in 1987, some models came with engines equipped with a Computer Controlled Coil Ignition (C 3 I) or Distributorless Ignition System (DIS).
Both DIS and C 3 I system consists of the coil pack, ignition module, crankshaft sensor, interrupter rings and ignition control module (ICM). All components are serviced as complete assemblies, although individual coils are available for Type 2 coil packs. Since the ICM controls the ignition timing, no timing adjustments are necessary or possible.