Ignition System L36 and L67
The EI system provides a spark to ignite the compressed
air/fuel mixture at the correct time in order to control fuel combustion.
The PCM controls the system's spark advance which provides optimum engine
performance, better fuel economy, and emissions control.
The EI system has several advantages over a mechanical distributor system:
| • | Remote mounting capability |
| • | No mechanical load on the engine |
| • | More coil cool down time between firing events |
| • | Elimination of timing adjustments |
| • | More ignition coil saturation time |
The EI system does not use the conventional distributor and coil. The
EI system consist of the following components:
| • | The ignition control module (ICM) |
| • | A dual Hall effect crankshaft position (CKP) sensor |
| • | The engine crankshaft balancer with interrupter rings |
| • | The ignition control (IC) and fuel metering portion of the powertrain
control module (PCM) |
Conventional ignition coils have one end of the secondary winding connected
to the engine ground. In this EI system, neither end is grounded. Instead,
each end of a coil's secondary winding is attached to a spark plug. Each cylinder
is paired with the one opposite, known as "companion" cylinders.
The spark plugs on the "companion" cylinders fire at the
same time when the coil discharges. This completes the series circuit. The
cylinder on compression is said to be the "event" cylinder; the
one on exhaust is the "waste" cylinder.
The "waste" cylinder requires very little of the available
energy to fire the plug. The "event" cylinder requires the remaining
energy. The same process occurs when the cylinders reverse roles. This method
of ignition is called a "waste spark" ignition system.
The polarity of the ignition coil primary and secondary windings is
fixed. Thus, one spark plug always fires with a forward current flow while
the "companion" plug fires with a reverse current flow. Conversely,
the distributor ignition (DI) system fires all of the plugs with the same
direction of current flow. Since 30% more voltage is needed in order to fire
a spark plug backwards, the ignition coil design is improved, with saturation
time and primary current flow increased. The EI system design allows higher
available ignition coil secondary voltage, more than 40,000 V at any
engine rpm.The polarity and the cylinder pressure determine the required spark
plug voltage.
It is possible for one spark plug to fire even if a plug wire from the
ignition coil is disconnected from the "companion" plug. The disconnected
plug wire acts as one plate of a capacitor, with the engine acting as the
other plate. These two "plates" are charged as a spark jumps across
the gap of the connected spark plug. The "plates" are then discharged
as the secondary energy is dissipated in an oscillating current across the
gap of the still-connected plug.
Secondary voltage requirements are very high with a disconnected plug.
The coil has enough reserve energy in order to fire the disconnected plug
at idle, but may fail at higher loads, where both of the "companion"
plugs may misfire.
