Figure 4-37.-High-energy timer and pole pieces.
coil pole piece (fig. 4-37). When the timer core teeth
align with the pole piece, a voltage pulse is induced in
the pickup winding. This pulse signals the module to
activate the primary coil current, inducting high voltage
in the secondary windings and ultimately firing the
spark plug. The module automatically y controls the dwell
period, stretching it as engine speed increases.
Therefore, the primary current reaches its maximum
strength at high engine speeds and reduces the chances
of high-speed misfire. The secondary coil energy
(35,000 volts) is greater than in conventional ignition
systems which allows increased spark duration. The
longer spark duration of the HEI system is instrumental
in firing lean and exhaust gas recirculation (EGR)
diluted fuel/air mixtures. The condenser within the HEI
distributor is provided for noise suppression only.
COMPUTERIZED IGNITION SYSTEM
Today, minicomputers are being used to control
many modern automotive systems. One example is
Fords electronic engine control system (EEC). This
system consists of an electronic control assembly
(ECA), seven monitoring sensors, a Dura Spark II
ignition module and coil, a special distributor assembly,
and an EGR system designed to operate on air pressure.
The ECA is a solid-state microcomputer consisting of
a processor and a calibration assembly. Refer to figure 4-38
while studying the operation of this system. The processor
continuously receives inputs from the seven sensors and
converts them into usable information that is received by
the calculating section of the computer. The processor
assembly also performs ignition timing, does Thermactor
and EGR flow calculations, processes this information,
and sends out signals to the ignition module and control
solenoids to adjust the timing and flow of the systems
accordingly. The calibration assembly contains the
memory and programming for the processor.
Processor inputs come from sensors that monitor
manifold pressure, barometric pressure, engine coolant
temperature, inlet air temperature, crankshaft position,
throttle position, and EGR valve position.
Manifold Absolute Pressure Sensor
This sensor detects changes in intake manifold
pressure that are caused by variances in engine speed,
engine load, or atmospheric pressure.
Barometric Pressure Sensor
Barometric pressure is monitored by a sensor
mounted on the fire wall. Measurements taken are
Figure 4-38.-Computer ignition components.