Injection Systems - Opel 1991 Astra Workshop Manual

Multi Point
Simultaneous
Sequential
Grouped
Single Point
Throttle Body
Operation
Injectors on the Bosch Motronic engine management systems receive battery voltage and are
triggered by the E.C.U. depending on the signals received from the various sensors attached
to the engine. Fuel pressure is constant (M.P.F.I. –
Injector opening frequency (Hz) and duration (pulse width) determine the amount of fuel
being delivered to the combustion chamber. Variations in pulse width and frequency ensure
that adequate fuel is supplied for efficient engine operation.
LONGER PULSE WIDTH
SHORTER PULSE WIDTH
Pulse rate and width will increase with increased engine rpm and load.
Duty Cycle
Duty cycle is the combination of pulse width and pulse rate, and is expressed as a percentage
of time "ON" and time "OFF" eg. If an injector was on for 10ms and closed for 90ms, the
duty cycle "ON" is 10% and the duty cycle "OFF" is 90%. The total on and off duty cycle
reading should be 100%.
Cranking Injector duration is longer during cranking (richer mixture) for easier starting
and to promote warm-up.
Idling Injector duration is longer at start-up if engine is cold, and gradually
decreases as engine warms up.
Acceleration Injector duration is longer at initial acceleration to prevent "flat spot"
Running Injection pulse is controlled by the E.C.U. depending on the signals received
from the various engine sensors.

Injection Systems

Injectors receive pulses from E.C.U. twice per engine cycle.
( Corsa 13 NE, 16NE, Astra 14SE, 16SE, 18XE, 20SHE )
Injectors are pulsed by E.C.U. once per engine cycle as per spark
plug firing order. ( Astra 20XE )
Injectors pulsed in groups or banks, once or twice per cycle
depending on system design
Single injector mounted on throttle body pulsed as per engine
requirement ( Astra 160 TBI )
= RICHER MIXTURE
= LEANER MIXTURE
250 to 300 Kpa).