Manifold Absolute Pressure (Map) Sensor; Powertrain Control Module - Chrysler 1998 Voyager Service Manual

8D - 6 IGNITION SYSTEM
GENERAL INFORMATION (Continued)
Fig. 9 Camshaft Position Sensor
cylinder 4 crankshaft timing marks follow. One cam-
shaft pulse after the 3 pulses indicates cylinder 5.
The 2 camshaft pulses after cylinder 5 signals cylin-
der 6 (Fig. 10). The PCM can synchronize on cylin-
ders 1 or 4.
When metal aligns with the sensor, voltage goes
low (less than 0.3 volts). When a notch aligns with
the sensor, voltage switches high (5.0 volts). As a
group of notches pass under the sensor, the voltage
switches from low (metal) to high (notch) then back
to low. The number of notches determine the amount
of pulses. If available, an oscilloscope can display the
square wave patterns of each timing event.
Top Dead Center (TDC) does not occur when
notches on the camshaft sprocket pass below the cyl-
inder. TDC occurs after the camshaft pulse (or
pulses) and after the 4 crankshaft pulses associated
with the particular cylinder. The arrows and cylinder
call outs on Figure 4 represent which cylinder the
flat spot and notches identify, they do not indicate
TDC position.
The camshaft position sensor is mounted in the
front of the timing case cover (Fig. 11).

MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR

The MAP sensor reacts to absolute pressure in the
intake manifold and provides an input voltage to the
Powertrain Control Module (PCM). As engine load
changes, manifold pressure varies. The changes in
engine load cause the MAP sensors resistance to
change. The change in MAP sensor resistance results
in a different input voltage to the PCM.
The input voltage level supplies the PCM with
information relating to ambient barometric pressure
during engine start-up (cranking) and engine load
while its operating. Based on MAP sensor voltage
and inputs from other sensors, the PCM adjusts
spark advance and the air-fuel mixture.
ENGINE COOLANT TEMPERATURE (ECT) SENSOR
The ECT sensor is located next to the thermostat
housing (Fig. 12). The sensor provides an input volt-
age to the Powertrain Control Module (PCM). The
Fig. 10 Camshaft Sprocket
Fig. 11 Camshaft Position Sensor Location
sensor is a variable resistance (thermistor) with a
range of -40°F to 265°F. As coolant temperature var-
ies, the sensors resistance changes, resulting in a dif-
ferent input voltage to the PCM.
The PCM contains different spark advance sched-
ules for cold and warm engine operation. The sched-
ules reduce engine emission and improve driveability.
When the engine is cold, the PCM will demand
slightly richer air-fuel mixtures and higher idle
speeds until normal operating temperatures are
reached.
The ECT sensor input is also used for cooling fan
control.
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