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FUEL SYSTEM
14 - 17
DUAL POINT F U E L I N J E C T I O N
Page
A/C S w i t c h - S B E C Input
19
Air Conditioning Clutch R e l a y - S B E C Output . . . . 22
Air Switching Solenoid—SBEC Output
. . . . . . . . .
22
Alternator—SBEC Output
23
Auto Shutdown (ASD) R e l a y — S B E C Output . . . . . 23
Battery Voltage—SBEC Input . . . . . . . . . . . . . . . .
19
Brake Light Switch—SBEC Input
. . .
. . . . . .
19
Canister Purge Solenoid—SBEC Output . . . . . . . .
23
Check Engine L a m p — S B E C Output
. . . . . . .
23
Coolant TemperatureSensor—SBEC Input
. . . . . .
19
E G R Solenoid—SBEC Output
23
EMR
L a m p — S B E C Output
23
Engine S p e e d — S B E C Input
19
Fuel Injectors—SBEC Output
. . . . . . . . . . . . . . . .
24
Fuel Pressure Regulator
30
Fuel P u m p — S B E C Output
. . . 24
General Information
". . . 17
GENERAL INFORMATION
The D u a l - P o i n t Electronic F u e l Injection System
(Fig. 1) is a computer regulated system t h a t provides
a precise air/fuel r a t i o for a l l d r i v i n g conditions. F u e l
is supplied t o the engine t h r o u g h two fuel injectors
i n the t h r o t t l e body.
A t the center of the system is t h e Single Board E n -
gine
Controller
(SBEC).
The SBEC
is a pre-
programmed, d i g i t a l computer t h a t regulates i g n i t i o n
t i m i n g , a i r - f u e l r a t i o , emission control devices, charg-
i n g system, speed control and idle speed. The SBEC
can adapt i t s p r o g r a m m i n g to meet changing operat-
i n g conditions.
Various sensors provide the inputs necessary for
t h e SBEC t o correctly regulate fuel flow at the injec-
tor. These include t h e M a n i f o l d Absolute
Pressure
sensor,
T h r o t t l e Position sensor,
Oxygen
Sensor,
Coolant Temperature sensor, and Vehicle Distance
sensor. I n a d d i t i o n t o the sensors, c e r t a i n switches
and relays provide i m p o r t a n t inputs. These include
t h e
Neutral-Safety
S w i t c h a n d A i r Conditioning
C l u t c h Relay.
A l l i n p u t s t o t h e Single Board Engine Controller
are converted i n t o signals. A i r - f u e l r a t i o , i g n i t i o n
t i m i n g and other controlled outputs are adjusted
based on these i n p u t s . The SBEC adjust the air-fuel
r a t i o by c h a n g i n g injector pulse w i d t h . Injector pulse
w i d t h is t h e period o f t i m e t h a t a n injector is ener-
gized by t h e SBEC.
The fuel injection system is a "Speed-Density" sys-
t e m . I n t h i s type of system engine R P M a n d manifold
absolute pressure are the p r i m a r y computer inputs
t h a t determine fuel injector pulse w i d t h . The SBEC
m a i n t a i n s desired air/fuel (14.7 t o 1) r a t i o by deter-
m i n i n g mass a i r flow and adjusts fuel injector pulse
w i d t h to o b t a i n the correct mass fuel flow.
Page
Idle Contact S w i t c h - S B E C Input . . . . . . . . . . . . .
20
Idle Speed Control (ISC) A c t u a t o r - S B E C Output . 24
Ignition C o i l - S B E C Output . . . . . . . . . . . . . . . . . .
24
Lock-Up Torque Convertor Solenoids—SBEC
Outputs
25
Manifold Absolute Pressure (MAP) S e n s o r — S B E C
Input
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
20
Modes of Operation
25
Overdrive S o l e n o i d - S B E C Outputs . . . . . . . . . . .
24
Oxygen Sensor ( 0
2
S e n s o r ) - S B E C Input
. . . . . .
20
Single Board Engine Controller (SBEC)
17
Throttle Body
27
Throttle Body Temperature S e n s o r — S B E C Input
(5.2L
and 5.9L Engines)
21
Throttle Position Sensor ( T P S ) - S B E C Input
. . . . 21
Transmission Gear Selection—SBEC Input
22
Vehicle Distance (Speed) S e n s o r - S B E C Input . . . 22
The combination of engine R P M and t h r o t t l e angle
( t h r o t t l e position i n p u t ) indicates engine a i r flow.
The M A P sensor i n p u t indicates a i r density. T h e
product of engine air flow and a i r density is mass a i r
flow. The product o f fuel pressure and injector pulse
w i d t h i s mass fuel flow.
SYSTEM
DIAGNOSIS
The
Single
Board
Module
Engine
Controller
(SBEC) tests m a n y of i t s o w n i n p u t and o u t p u t cir-
cuits. I f a f a u l t is found i n a major system, t h i s i n -
f o r m a t i o n is stored i n memory. I n f o r m a t i o n about
t h i s f a u l t can be displayed to a technician by means
of t h e i n s t r u m e n t panel Check Engine l a m p or b y
connecting the Diagnostic Readout Box I I ( D R B I I )
and reading descriptions o f any faults w h i c h have
been stored i n memory. Refer to the Service Diagnos-
tic Tester and accompanying manuals. The Service
Diagnostic Tester plugs i n t o a diagnostic connector
inside the engine compartment.
SINGLE BOARD ENGINE CONTROLLER (SBEC)
The Single Board Engine Controller ( S B E C -
F i g .
2) is a d i g i t a l computer c o n t a i n i n g a microprocessor.
I t receives i n p u t signals f r o m various switches a n d
sensors. Based on these inputs, the SBEC regulates
various engine and vehicle operations t h r o u g h differ-
ent system components t h a t are referred to as " S B E C
O u t p u t s " .
The SBEC controls fuel injector pulse w i d t h (air-
fuel r a t i o ) based on inputs received from sensors t h a t
react to exhaust gas oxygen content, coolant temper-
ature, m a n i f o l d absolute pressure, battery voltage,
engine speed, t h r o t t l e position, t h r o t t l e body temper-
ature (5.2L and 5.9L engines) battery voltage, a n d
i n p u t s from switches t h a t are triggered b y a i r condi
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