JLG 4394RT Service Manual - Manual (Page 78)

SECTION 3 - CHASSIS & SCISSOR ARMS
3-42 – JLG Sizzor – 3121133
ELECTRONIC IGNITION
The electronic ignition system controls fuel combustion by
providing a spark to ignite the compressed air/fuel
w mix-
ture at the correct time. To provide optimum engine perfor-
mance, fuel economy, and control of exhaust emissions,
the ECM controls the spark advance of the ignition system.
Electronic ignition has the following advantages over a
mechanical distributor system:
• No moving parts
• Less maintenance
• Remote mounting capability
• No mechanical load on the engine
• More coil cooldown time between firing events
• Elimination of mechanical timing adjustments
• Increased available ignition coil saturation time
IGNITION COIL
The electronic ignition system uses a coil pack with one
ignition coil for each two cylinders in the engine. Each cyl-
inder is paired with its opposing cylinder in the firing order,
so that one cylinder on compression fires simultaneously
with the opposing cylinder on exhaust. The spark that
occurs in the cylinder on the exhaust stroke is referred to
as a "waste spark."
The primary coils in the coil pack are triggered by the
"Ignition Coil Feed #1" and "Ignition Coil Feed #2" Signals
from the ECM.
ENGINE CONTROL MODULE (ECM)
The ECM is responsible for maintaining proper spark and
fuel injection timing for all operating conditions. To provide
optimum operation and emissions, the ECM monitors the
input signals from the following components in order to
calculate spark timing:
• Engine coolant temperature (ECT) sensor
• Intake air temperature (IAT) sensor
• Throttle position sensor
• Crankshaft position sensor