Dynasty L4-153 2.5L SOHC (1988)
Intake Air Temperature (IAT) Sensor: Description and Operation
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR
1988-89
On 1988 models, the MAP sensor is mounted under hood on the dash panel. On 1989 models, the MAP sensor is mounted under hood on the strut
tower. The MAP sensor monitors intake manifold vacuum through a line connected to the throttle body. The sensor converts manifold vacuum
(negative pressure) and barometric pressure into electrical signals and transmits these signals to the SMEC. The module uses these signals to monitor
engine load and is used with data from other sensors to determine correct air fuel mixture for vehicle operating conditions.
OXYGEN SENSOR
The oxygen sensor produces voltage signals when exposed to oxygen in the exhaust gasses. The oxygen content in the exhaust gasses is directly
proportional to the air fuel mixture entering the engine, and the voltage signal produced by the sensor is inversely proportional to the amount of
oxygen remaining in the exhaust gasses. The logic module or SMEC uses these signals to determine air fuel mixtures entering the engine.
The oxygen sensor is mounted in the exhaust manifold, and the sensing element must be heated by exhaust gasses before the sensor begins to produce
voltage signals. When exhaust gas oxygen content is high (lean mixtures), the sensor produces a low voltage. When oxygen content is low (rich
mixtures), the sensor produces a higher voltage.
COOLANT TEMPERATURE SENSOR
The coolant temperature sensor is mounted in the thermostat housing and allows the logic module or SMEC to monitor engine operating temperature
in order to provide proper air/fuel mixtures. The sensor provides a variable resistance which is proportional to coolant temperature. When the engine
is cold and sensor resistance is low, the logic module or SMEC provides richer air/fuel mixtures and increases engine idle speed to provide acceptable
cold engine performance and allow quick warm up. On 1986 - 87 models, when coolant temperature and sensor resistance increase, the logic module
provides leaner air/fuel mixtures and lowers engine idle speed to provide proper exhaust emission control and increased fuel economy. On 1988 - 89
models, the coolant temperature sensor is also used for cooling fan control.
THROTTLE BODY TEMPERATURE SENSOR
The throttle body mounted temperature sensor allows the logic module or SMEC to monitor fuel temperature. The logic module or SMEC uses this
information to provide the proper air/fuel mixtures for a hot restart condition.
THROTTLE POSITION SENSOR (TPS)
The TPS is mounted on the throttle body and is senses the angle of the throttle plate opening. The sensor produces a voltage signal which increases
and decreases according to throttle position. The logic module or SMEC uses these voltage signals to tailor air/fuel mixtures for varying conditions
such as idle, wide open throttle, acceleration and deceleration.
SWITCH INPUTS
Various switches provide information to the logic module or SMEC. These switches include the idle, neutral safety, A/C compressor clutch speed
control (1988) and brake lamp switches. If one or more of these switches is sensed as being On, the logic module or SMEC signals the idle speed
motor to change idle speed to a pre-set RPM. In addition, when the A/C is on and the throttle plate is above a specified angle, the wide open throttle
cut-out relay prevents the A/C clutch from being energized until throttle angle is reduced.
