Chrysler Le Baron, Dodge Dynasty, Plymouth Acclaim. Manual - part 51
tially energizes all injectors at the same time. Once
the PCM determines crankshaft position, it begins
energizing the injectors in sequence.
Battery voltage is supplied to the injectors through
the ASD relay. The PCM provides the ground path
for the injectors. By switching the ground path on
and off, the PCM adjusts injector pulse width. Pulse
width is the amount of time the injector is energized.
The PCM adjusts injector pulse width based on in-
puts it receives.
IGNITION COIL—PCM OUTPUT
The auto shutdown (ASD) relay provides battery
voltage to the ignition coil. The PCM provides a
ground contact (circuit) for energizing coil. When the
PCM breaks the contact, the energy in the coil pri-
mary transfers to the secondary causing the spark.
The PCM will de-energize the ASD relay if it does
not receive an input from the distributor pick-up. Re-
fer to Auto Shutdown (ASD) Relay/Fuel Pump Re-
lay—PCM Output in this section for relay operation.
The ignition coil is mounted on a bracket next to
the air cleaner (Fig. 18).
PART THROTTLE UNLOCK SOLENOID—PCM
OUTPUT
Three-speed automatic transaxles use a part throt-
tle unlock solenoid. The PCM controls the lock-up of
the torque convertor through the part throttle unlock
solenoid. The transaxle is locked up only in direct
drive mode. Refer to Group 21 for transaxle informa-
tion.
RADIATOR FAN RELAY—PCM OUTPUT
The radiator fan is energized by the PCM through
the radiator fan relay. The radiator fan relay is lo-
cated on the drivers side fender well near to the
PCM. The PCM grounds the relay when engine cool-
ant reaches a predetermined temperature or the air
conditioning system turns on.
On AA body vehicles, the relay is located next to
the drivers side strut tower (Fig. 13).
On AC, AG and AJ body vehicles, the relay is lo-
cated in the power distribution center (Fig. 12 or Fig.
14).
SPEED CONTROL SOLENOIDS—PCM OUTPUT
The speed control vacuum and vent solenoids are
operated by the PCM. When the PCM supplies a
ground to the vacuum and vent solenoids, the speed
control system opens the throttle blade. When the
PCM supplies a ground only to the vent solenoid, the
throttle blade holds position. When the PCM removes
the ground from both the vacuum and vent solenoids,
the throttle blade closes. The PCM balances the two
solenoids to maintain the set speed. Refer to Group
8H for speed control information.
TACHOMETER—PCM OUTPUT
The PCM supplies engine RPM to the instrument
panel tachometer through the CCD Bus. The CCD
Bus is a communications port. Various modules use
the CCD Bus to exchange information. Refer to
Group 8E for more information.
MODES OF OPERATION
As input signals to the PCM change, the PCM ad-
justs its response to the output devices. For example,
the PCM must calculate a different injector pulse
width and ignition timing for idle than for wide open
throttle (WOT). There are several different modes of
operation that determine how the PCM responds to
the various input signals.
There are two different areas of operation, OPEN
LOOP and CLOSED LOOP.
During OPEN LOOP modes the PCM receives in-
put signals and responds according to preset PCM
programming. Input from the oxygen (O
2
) sensor is
not monitored during OPEN LOOP modes.
During CLOSED LOOP modes the PCM does mon-
itor the oxygen (O
2
) sensor input. This input indi-
cates to the PCM if the injector pulse width results
in an air-fuel ratio of 14.7 parts air to 1 part fuel. By
monitoring the exhaust oxygen content through the
O
2
sensor, the PCM can fine tune the injector pulse
width. Fine tuning injector pulse width allows the
PCM to achieve optimum fuel economy combined
with low emissions.
The 3.0L sequential MPI system has the following
modes of operation:
• Ignition switch ON—Zero-RPM
• Engine start-up
• Engine warm-up
• Cruise (Idle)
• Acceleration
• Deceleration
• Wide Open Throttle
• Ignition switch OFF
Fig. 18 Ignition Coil
Ä
FUEL SYSTEMS
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