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voltage is not supplied to the fuel p u m p , i g n i t i o n coil,
fuel injector or oxygen sensor h e a t i n g relay.
Engine Start-Up Mode
This i s a n O P E N LOOP mode. The f o l l o w i n g ac-
tions occur when t h e starter motor i s engaged.
I f t h e SBEC receives a d i s t r i b u t o r signal i t w i l l en-
ergize t h e auto shutdown (ASD) relay to supply bat-
t e r y voltage to the fuel pump, fuel injector i g n i t i o n
coil, and oxygen sensor heating element. I f t h e SBEC
does not receive a d i s t r i b u t o r i n p u t , t h e A S D relay
w i l l not be energized.
W h e n t h e engine is operating a n d i d l i n g w i t h i n
±64 R P M of the target RPM, t h e SBEC compares t h e
c u r r e n t M A P value w i t h the atmospheric pressure
value i t received d u r i n g the Key-On mode. I f a m i n -
i m u m difference between the t w o i s not detected, a
pneumatic f a u l t code is set i n t o memory.
Once t h e ASD relay has been energized t h e SBEC:
• Supplies a ground p a t h to t h e injector a n d the i n -
jector is pulsed six times per engine r e v o l u t i o n i n -
stead of t h e n o r m a l three pulses per r e v o l u t i o n .
• determines injector pulse w i d t h based o n coolant
temperature, barometric pressure ( M A P sensor), and
the n u m b e r of engine revolutions since c r a n k i n g was
i n i t i a t e d .
• M o n i t o r s the coolant temperature sensor, d i s t r i b u -
t o r pick-up, M A P sensor, and t h r o t t l e position sensor
to determine correct i g n i t i o n t i m i n g .
Engine Warm-Up Mode
This i s a O P E N L O O P mode. The f o l l o w i n g i n p u t s
are received by the SBEC:
• coolant temperature
• idle contact switch
• m a n i f o l d absolute pressure
• engine speed (distributor pick-up)
• t h r o t t l e position
• gear position (automatic transmission)
• A/C switch
• battery voltage
The SBEC provides a ground p a t h for t h e injector
to precisely control injector pulse w i d t h (by s w i t c h i n g
the ground on and off) and fires the injector three
times per engine revolution. The SBEC controls en-
gine idle speed, t h r o t t l e stop angle, and i g n i t i o n t i m -
i n g .
The SBEC controls engine idle speed a n d t h r o t t l e
stop angle. F o r vehicles equipped w i t h a m a n u a l
transmission, t h e up-shift indicator l a m p i s con-
trolled b y the SBEC according t o engine speed a n d
load.
Cruise Mode
W h e n the engine is a t operating t e m p e r a t u r e t h i s
is a CLOSED LOOP mode. D u r i n g c r u i s i n g speed t h e
following inputs are received by the SBEC:
• coolant temperature
• m a n i f o l d absolute pressure
• engine speed
• t h r o t t l e position
• exhaust gas oxygen content
• gear position (automatic transmission)
• A/C control positions
The SBEC provides a g r o u n d p a t h for t h e injector
to precisely control injector pulse w i d t h a n d fires the
injector three times per engine r e v o l u t i o n . The SBEC
controls engine idle speed, t h r o t t l e stop angle, and
i g n i t i o n t i m i n g . The SBEC controls the air/fuel m i x -
t u r e r a t i o according to t h e oxygen content i n the ex-
haust gas.
For vehicles equipped w i t h a m a n u a l transmission,
t h e up-shift indicator l a m p is controlled by t h e SBEC
according to engine speed a n d load.
Acceleration Mode
This i s a n O P E N L O O P mode. The SBEC recog-
nizes a n a b r u p t increase i n t h r o t t l e position or M A P
pressure as a demand for increased engine o u t p u t
and vehicle acceleration. The SBEC increases injec-
t o r pulse w i d t h i n response to increased fuel demand.
Deceleration Mode
This i s a O P E N L O O P mode. D u r i n g deceleration
t h e f o l l o w i n g inputs are received by the SBEC:
• coolant temperature
• m a n i f o l d absolute pressure
• idle contact switch
• engine speed
• t h r o t t l e position
• exhaust gas oxygen content
• gear position (automatic transmission)
• A/C control positions
W h e n t h e SBEC receives a closed t h r o t t l e i n p u t a t
t h e same t i m e i t senses a n a b r u p t decrease i n m a n i -
fold pressure from the M A P sensor (indicating a h a r d
deceleration) i t may reduce injector f i r i n g to once per
engine r e v o l u t i o n t o lean t h e air-fuel m i x t u r e as
sensed t h r o u g h the 0
2
sensor.
The SBEC grounds t h e EGR and evaporative purge
solenoids stopping E G R and canister purge functions.
The SBEC may cycle a i r s w i t c h i n g solenoid for short
periods o f t i m e i n response to t h e M A P sensor send-
i n g a h i g h vacuum signal.
Wide Open Throttle Mode
This is a n O P E N L O O P mode. D u r i n g wide-open-
t h r o t t l e operation, t h e f o l l o w i n g i n p u t s are received
by the SBEC:
• coolant temperature
• m a n i f o l d absolute pressure
• engine speed
• t h r o t t l e position
W h e n t h e SBEC senses wide open t h r o t t l e condi-
t i o n t h r o u g h the TPS i t w i l l provide a ground for the
EGR solenoid and evaporative
canister purge sole-
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