Chrysler 1998 Viper RT/10 Owner's Manual page 291

S R
IGNITION SYSTEM 8D - 5
D E S C R I P T I O N A N D O P E R A T I O N ( C o n t i n u e d )
ENGINE COOLANT TEMPERATURE SENSOR
The engine coolant temperature sensor threads
into the cylinder head behind the Power Steering
Pump (Fig. 11). The sensor provides an i n p u t to the
Powertrain Control Module (PCM). As coolant tem-
perature varies, the sensor resistance changes,
resulting i n a different i n p u t voltage to the P C M .
U n t i l the engine reaches normal operating temper-
ature, the P C M demands slightly richer air-fuel mix-
tures and higher idle speeds.
This sensor is also used for cooling fan control.
Fig. 11 Engine Coolant Temperature Sensor
INTAKE AIR TEMPERATURE SENSOR
The Intake A i r Temperature (IAT) sensor measures
the temperature of the air as i t enters the engine.
The sensor supplies one of the inputs the P C M uses
to determine injector pulse-width.
1ANIF0L0 ABSOLUTE PRESSURE SENSOR
The Powertrain Control Module (PCM) supplies 5
volts to the M A P sensor. Intake manifold pressure is
a function of barometric pressure. The M A P sensor
converts pressure into voltage. The P C M monitors
the M A P sensor output voltage. As vacuum increases,
M A P sensor voltage decreases proportionately. Also,
as vacuum decreases, M A P sensor voltage increases
proportionately.
D u r i n g Key-On, before cranking the engine, the
P C M determines atmospheric air pressure from the
M A P sensor voltage. While the engine operates, the
P C M determines intake manifold pressure relative to
atmospheric pressure. Also, atmospheric pressure is
updated at wide-open-throttle. Based on M A P sensor
voltage and inputs from other sensors, the P C M
adjusts spark advance and air/fuel mixture.
The M A P sensor (Fig. 12) mounts to the drivers
side intake manifold plenum.
Fig. 12 Map Sensor
THROTTLE POSITION SENSOR (TPS)
The TPS mounts to the side of the driver side
t h r o t t l e body (Fig. 13). The TPS connects to the
t h r o t t l e blade shaft. The TPS is a variable resistor
t h a t provides the Powertrain Control Module (PCM)
w i t h an i n p u t signal (voltage). The signal represents
t h r o t t l e blade position. As the position of the t h r o t t l e
blade changes, the resistance of the TPS changes.
The P C M supplies approximately 5 volts to the
TPS. The TPS output voltage (input signal to the
powertrain control module) represents t h r o t t l e blade
position. The TPS output voltage to the P C M varies
from approximately 0.38 volts to 1.03 volts at m i n i -
m u m t h r o t t l e opening (idle) to a m a x i m u m of 3.1
volts to 4.0 volts at wide open throttle.
Along w i t h inputs from other sensors, the P C M
uses the TPS i n p u t to determine current engine oper-
ating conditions. The P C M also adjusts fuel injector
pulse w i d t h and ignition t i m i n g based on these
inputs.
Fig. 13 Throttle Position Sensor