Pontiac Fiero 1988 Service Manual page 414

IGNITION SYSTEM 6D4-1
SECTION 6D4
IGNITION SYSTEM
CONTENTS
General Description 6D4-1
Ignition System 6D4-1
Distributor Ignition 6D4-1
Distributorless Ignition 6D4-1
Diagnosis
6D4-3
Ignition System 6D4-3
HEI Distributor 6D4-4
Distributorless Ignition 6D4-4
Service Procedures
6D4-4
Ignition System 6D4-4
Distributor Ignition 6D4-4
Distributorless Ignition 6D4-5
On-Car Service
6D4-6
Distributorless Ignition - 2.5L 6D4-6
Ignition Coil ............................................... 6D4-6
Ignition Module 6D4-6
Sensor 6D4-6
Ignition System - 2.8L 6D4-6
Distributor
6D4-6
Ignition Coil
6D4-6
GENERAL DESCRIPTION
The engine electrical system includes the battery,
ignition (primary and secondary), starter (and related
wiring) and the generator (and related wiring).
Diagnostic charts (see Section 6D) will aid in
trouble-shooting system faults. When a fault is traced
to a particular component, refer to that components'
section of the service manual.
IGNITION SYSTEM
Distributor Ignition
The ignition circuit consists of the battery,
distributor, ignition switch, spark plugs and primary
and secondary wiring. Refer to the Battery portion of
this section for battery information.
HEI Distributor
The High Energy Ignition (HEI) distributor with
Electronic Spark Timing (EST), used on most engines,
combines all ignition components in one unit. The
ignition coil is in the distributor cap and connects
through a resistance brush to the rotor.
The distributor has an internal magnetic pick-up
assembly which contains a permanent magnet, a pole
piece with internal teeth and a pick-up coil. When the
teeth of the timer core, rotating inside the pole piece,
line up with the teeth of the pole piece, an induced
voltage in the pick-up coil signals the electronic module
to trigger the coil primary circuit. The primary current
decreases and a high voltage is induced in the ignition
coil secondary winding. This voltage is directed
through the rotor and secondary leads to fire the spark
plugs. The capacitor in the distributor is for radio noise
suppression.
All spark timing changes in the HEI (EST)
distributor are done electronically by an 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 advance is
used. Further (EST) information is found in sections
6E Emissions Control, and 8A Electrical
Troubleshooting.
IGNITION SYSTEM
Distributorless Ignition
Distributorless ignition systems use a " waste
spark" method of spark distribution. Each cylinder is
paired with its opposing cylinder in the firing order, so
that one cylinder on compression fires simultaneously
with its opposing cylinder on exhaust. Since the
cylinder on exhaust requires very little of the available
voltage to fire its plug, most of the voltage is used to
fire the cylinder on compression. The process reverses
when the cylinders reverse roles. There are two or three
coils for a 4-cylinder or 6-cylinder engine (DIS - Direct
Ignition System) and three coils for a 6-cylinder engine
(CT).
Direct Ignition System
Components of the Direct Ignition System are a
coil pack, ignition module, crankshaft reluctor ring,
magnetic sensor, and the ECM. The coil pack consists
of two separate, interchangeable, ignition coils. These
coils operate in the same manner as previous coils. Two
coils are needed because each coil only fires for two
cylinders. The ignition module is located under the coil
pack and is connected to the ECM by a 6-pin
connector. The ignition module controls the primary
circuit to the coils, turning them on and off, and
controls spark timing below 400 rpm and if the ECM
bypass circuit becomes open or grounded (see Section
6E2).
The magnetic pickup sensor inserts through the
engine block, just above the pan rail, in proximity to