Ignition System; Description - Suzuki GSX-R750 Service Manual

7-20 ELECTRICAL SYSTEM

IGNITION SYSTEM

DESCRIPTION

The ignition system is controlled by the ECM. The system is called fully transistorized ignition system which
decides accurate ignition timing according to the engine rpm, gear position and throttle position.
The ignition system has four ignition coils called DIRECT IGNITION. In this system, the plug cap and ignition
coil for each cylinder are unified.
This system consists of the crankshaft position sensor (pick up coil), ECM, ignition coils/spark plug caps and
spark plugs.
1. The ignition coil power source is supplied through the side-stand relay from the battery, which means that
the ignition coil power source is controlled by the side-stand and gear position switch.
2. The ignition timing is accurately controlled by the throttle position and engine rpm.
In addition to this basic map, the engine coolant temp. sensor affects the ignition timing when the engine is
started using fast idle system with coolant temperature low.
3. The ignition timing is also compensated according to the gear position and throttle position.
The following devices affects the ignition timing.
Crankshaft position sensor:
The pick up coil is provided at the left end of the crankshaft, which produces signal waveform when meeting
with the protrusion on the generator rotor.
The generated wave is sent to the ECM that calculates the engine rpm.
This signal decides the ignition timing and signal to the tachometer.
Throttle position sensor:
This sensor is set at the throttle body, and it is a kind of variable resistor, which changes resistance value
according to the throttle opening. With this signal, the ECM decides the ignition timing in response to the
engine rpm.
The ignition timing map is composed of two factors, throttle position and engine rpm.
Gear position switch:
The gear position switch has a different resistance for each gear, and ECM understands the gear position.
The ECM selects the ignition timing when the gear position is changed.
Engine coolant temp. sensor:
This sensor changes ignition timing to advance side when the temperature is low. The timing advance returns
to the basic map when engine coolant temperature rise.