Ignition system

Summary

The DeLorean DMC-12 is equipped with a Bosch electronic ignition system. This breakerless ignition system is similar to a conventional ignition system except for the following modifications:

The breaker points in the distributor have been replaced by a pulse generator consisting of a stator, an induction coil, and a trigger wheel. The pulse converter is connected to an electronic control unit (ECU) module in which the signal from the distributor is converted and amplified. The ECU module is connected to a high-voltage ignition coil.

Distributor

The distributor contains a pulse generator which corresponds to the breaker points in a conventional distributor. The trigger wheel is attached to the distributor shaft and is designed with six fingers (poles). The stator, induction coil, and magnet are formed into one unit which is attached to the distributor plate. The stator is also designed with six fingers (poles).

When the trigger wheel rotates, an alternating voltage is produced in the pulse generator. The pules is transmitted to the ECU module and its voltage will vary between 0.3 volts and 100 volts depending on engine speed.

The alternating voltage is produced by the trigger wheel passing through a magnetic field which creates a voltage in the induction coil. As the pole on the trigger wheel approaches the pole on the stator, a positive voltage is produced. The voltage then reverses polarity as the poles separate. The ECU module creates secondary ignition spark when the poles are directly aligned with each other.

Electronic Control Unit Module

The ECU module controls the operation of the ignition coil and determines the proper dwell angle. The module is a fully electronic sealed component which does not utilize any moving parts. It is located in the bottom of the module compartment behind the driver's seat.

The module monitors engine operation by the varying voltage pulses it receives from the pulse generator in the distributor. This information is electronically analyzed and the proper dwell angle is established for different engine speeds. By varying the dwell angle, the coil is capable of operating at maximum efficiency.

After the dwell angle is determined, the output transistor turns the ignition coil primary circuit on and off. When current is flowing in the primary circuit, a magnetic field is built up within the coil. As current flow stops, the field collapses and the secondary ignition spark takes place. The secondary ignition spark delivered from the coil high tension terminal is routed to the proper cylinder by the distributor rotor and cap.

Compensating resistor

A dual-ballast resistor is used to control primary circuit voltage and current flow. It is attached to the firewall at the left front corner of the engine compartment.

When the ignition switch is in the "run" position, the current flow is reduced by the resistor to prevent overheating of the coil during operation. To provide increased coil voltage for starting the engine, one half of the resistor is bypassed during engine cranking. By reducing the circuit resistance, the coil primary voltage and current will increase, thus increasing secondary output voltage. A defective or improperly installed compensating resistor will cause premature ignition coil failure.

Ignition timing advance

The Bosch distributor provides timing advance by means of a centrifugal advance unit and a vacuum advance unit the same as a conventional distributor.

Spark plugs and wires

Bosch HR6DS spark plugs are used with carbon core secondary wiring. Spark plugs are gapped at 0.6 to 0.7 millimetres (0.024 - 0.028 inches).

Distributor cap and rotor

A conventional distributor cap is used with a 5,000 Ihm rotor for radio suppression. The ignition distributor is located under the intake manifold on the left cylinder head and is driven by the left camshaft. Due to the design of the crankshaft used in the PRV-V6 engine, the distributor has unequal spacing of the ignition secondary terminals. When viewing primary and secondary patterns on an oscilloscope, the patterns will have unequal dwell spacing.

Ignition coil

The ignition coil is located behind the black plastic cover in the right front corner of the engine compartment.

Specifications

Distributor

Rotation: clockwise Firing order: 1-6-3-5-2-4

Compensation resistor value: 0.5 Ohm each (1.0 Ohm total)

Basic ignition timing: 13+2 degrees BTDC at 775 +50 RPM (vacuum advance disconnected)

Induction coil resistance: 895 - 1,285 Ohm

Trigger/stator pole air gap: 0.25mm

Spark advance -- vacuum (at idle speed): 5 in.hg. = 3 degrees; 10 in.hg. = 12 degrees; 15 in.hg. = 20 degrees

Spark advance -- mechanical: 1000RPM (engine) = 0 degrees; 2000 RPM (engine) = 10 degrees; 3000 RPM (engine) = 14 degrees; 4000 RPM (engine) = 20 degrees

Rotor: 5000 Ohms

Coil

Primary winding resistance: 0.95-1.4 Ohm at 20 degrees C

Secondary winding resistance: 5.5-8.5 k Ohm

Average current value through primary winding at idle: 3.2 Amps

Spark plugs

Torque specifications: 17.5-20 NM (13-15 ft.lb.)

Gap: 0.6-0.7 mm (0.024-0.028 in.)