Dodge D150 1990 Service Manual page 705

14 - 22 FUEL SYSTEM •
TRANSMISSION GEAR SELECTION-SBEC INPUT
The n e u t r a l safety switch (Fig. 11) is located on the
transmission housing a n d provides a n i n p u t t o t h e
SBEC t h a t indicates the automatic transmission is i n
Park, N e u t r a l or a drive gear selection. T h i s i n p u t is
used to determine idle speed (varying w i t h gear se-
lection), fuel injector pulse w i d t h , and i g n i t i o n t i m -
i n g advance. Refer t o group 2 1 Transmissions, for
testing, replacement, and adjustment i n f o r m a t i o n .
Fig. 11 Neutral Safety Switch
VEHICLE DISTANCE (SPEED) SENSOR-SBEC
INPUT
The distance sensor (Fig. 12) is located i n t h e ex-
tension housing of the transmission. T h e sensor i n -
p u t is used by t h e Single Board Engine Controller
(SBEC) t o determine vehicle speed and distance t r a v -
eled.
The distance sensor generates 8 pulses per sensor
revolution. These signals are interpreted, i n conjunc-
t i o n w i t h a closed t h r o t t l e signal from t h e t h r o t t l e
position sensor, by t h e engine controller t o differen-
tiate between a closed t h r o t t l e deceleration a n d a
n o r m a l idle (vehicle stopped) condition. U n d e r decel-
eration conditions, t h e engine controller controls t h e
ISC motor to m a i n t a i n a desired M A P value. Under
idle conditions, t h e engine controller adjusts the A I S
motor t o m a i n t a i n - a desired engine speed.
AIR CONDITIONING CLUTCH RELAY-SBEC
OUTPUT
The Single Board Engine Controller (SBEC) con-
trols t h e a i r conditioning compressor t h r o u g h t h e
A/C clutch relay (Fig. 13). B y s w i t c h i n g t h e ground
p a t h for relay on and off, t h e SBEC is able to cycle
the a i r conditioning compressor c l u t c h based on
changes i n engine operating conditions.
The relay is energized w h e n t h e A/C switch is
closed (A/C has been selected) and the blower motor
switch is i n the on position. I f , d u r i n g A/C operation,
Fig. 12 Vehicle Distance Sensor
PART THROTTLE ^ A/C CLUTCH CUTOUT STARTER
UNLOCK RELAY ^ RELAY RELAY
Fig. 13 A/C Clutch, ASD, Starter and Part Throttle
Un-lock Relays
the SBEC senses l o w idle speeds or a wide open
t h r o t t l e condition, i t w i l l de-energize the relay pre-
v e n t i n g a i r c o n d i t i o n i n g clutch engagement u n t i l t h e
idle speed increases or wide open t h r o t t l e condition
no longer exists.
AIR SWITCHING SOLENQID-SBEC OUTPUT
The SBEC controls t h e upstream or downstream
discharge of a i r f r o m t h e a i r pump t h r o u g h t h e a i r
s w i t c h i n g solenoid ( F i g . 14). The solenoid controls
the flow of v a c u u m to t h e a i r switching/relief valve
of the a i r p u m p system.
W h e n t h e a i r s w i t c h i n g system is i n t h e down-
stream mode o f operation t h e solenoid is n o t ener-
gized a n d v a c u u m is n o t supplied to t h e a i r
switching/relief valve. D u r i n g downstream operation
air p u m p o u t p u t is directed to the catalytic conver-
ter.
W h e n t h e a i r s w i t c h i n g system is i n t h e upstream
mode of operation, t h e solenoid is energized and vac-
u u m is supplied t o t h e a i r switching/relief valve.