BOMBARDIER Johnson 90 Service Manual page 81

ENGINE CONTROL SYSTEM
ELECTRONIC FUEL INJECTION SYSTEM
ECM
Rectifier
and
regulator
Battery
ECM
IAC Valva
Sensor/ switch
signal input
Duty cycle slgnal for fuel pump
(example: 20% duty)
"ON" time
x
100 = duty (%)
1 cycle time
OFF
ON
o.a
ms
hf!
h1
hd ••
Time
4
ms (1cycle)
CONTROL MODE
BEFORE START:
The IAC valve is closed (0% duty) when engine is not running (but ignition switch is ON).
WHEN CRANKING:
The IAC valve is controlled to operate at approx. 80% duty.
AFTER START (FAST-IDLE FUNCTION):
The IAC valve is controlled to operate at approx. 25 - 50% duty until the timer, which was set according
to cylinder temperature at cranking, expires.
WHEN IDLING / TROLLING:
The IAC valve is controlled so that the engine speed is stable at the idling / trolling speed specified. Dur­
ing this period, the IAC valve has a duty cycle of approx. 15% but will vary slightly as idling / trolling con­
ditions change.
WHEN RUNNING (NORMAL OPERATION):
The IAC valve is controlled to operate at 20 - 50% duty, which depends on the current engine condi­
tions.
WHEN DECELERATING (DASHPOT EFFECT):
When the throttle valve is suddenly returned to full close and the CTP switch signal changes to "ON", the
IAC valve operates at a controlled gradual return to idle / troll operating duty to prevent engine stalling or
unstable running.
NOTE:
Due to the limited intake air flow from the /AC passage and in order to effectively use both the "Dashpot
effect" and "Fast-idle function", the bypass air screw must be adjusted to provide IAC va/ve operation at
approx. 15% duty at the engine idling / trolling specification. See page 2-15 for the bypass air screw
adjustment procedure.
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