1993 CHEVROLET PLYMOUTH ACCLAIM coolant temperature

controlled outputs. The PCM adjusts the air-fuel ra-
tio by changing injector pulse width. Injector pulse
width is the time an injector is energized.
SYSTEM DIAGNOSIS
The PCM tests many of its own input and output
circuits. If a fault is found in a major system, the in-
formation is stored in memory. Technicians can dis-
play fault information through the malfunction
indicator lamp (instrument panel Check Engine
lamp). Also, the technician can read fault informa-
tion by connecting the DRBII scan tool to the data
link connector. For diagnostic trouble code informa-
tion, refer to the 2.2L Turbo III Multi-Port Fuel In-
jectionÐOn-Board Diagnostics section of this group.
CCD BUS
Various modules exchange information through a
communications port called the CCD Bus. The pow-
ertrain control module (PCM) transmits vehicle load
data on the CCD Bus.
POWERTRAIN CONTROL MODULE
The powertrain control module (PCM) is a digital
computer containing a microprocessor (Fig. 2). The
PCM receives input signals from various switches
and sensors that are referred to as PCM Inputs.
Based on these inputs, the PCM adjusts various en-
gine and vehicle operations through devices that are referred to as PCM Outputs.
PCM Inputs:
² Air Conditioning Controls
² Battery Voltage
² Brake Switch
² Camshaft Position Sensor
² Crankshaft Position Sensor
² Charge Air Temperature Sensor
² Engine Coolant Temperature Sensor
² Knock Sensor
Fig. 1 Electronic Fuel Injection Components
Fig. 2 PCM
14 - 84 FUEL SYSTEMS Ä

² Manifold Absolute Pressure (MAP) Sensor
² Oxygen Sensor
² SCI Receive
² Speed Control System Controls
² Throttle Position Sensor
² Vehicle Speed Sensor
PCM Outputs:
² Air Conditioning Clutch Relay
² Generator Field
² Idle Air Control Motor
² Auto Shutdown (ASD) Relay
² Barometric Read Solenoid
² Canister Purge Solenoid
² Malfunction Indicator Lamp (Check Engine Lamp)
² Data Link Connector
² Fuel Injectors
² Ignition Coil
² Radiator Fan Relay
² Speed Control Solenoids
² Tachometer Output
² Wastegate Solenoid
Based on inputs it receives, the PCM adjusts fuel
injector pulse width, idle speed, ignition spark ad-
vance, ignition coil dwell and canister purge opera-
tion. The PCM regulates operation of the cooling fan,
A/C and speed control systems. The PCM changes
generator charge rate by adjusting the generator
field. The PCM adjusts injector pulse width (air-fuel ra-
tio) based on the following inputs.
² battery voltage
² engine coolant temperature
² exhaust gas content
² engine speed (crankshaft position sensor)
² manifold absolute pressure
² throttle position
The PCM adjusts ignition timing based on the fol-
lowing inputs.
² engine coolant temperature
² knock sensor
² engine speed (crankshaft position sensor)
² manifold absolute pressure
² throttle position
The Automatic Shut Down (ASD) and Fuel Pump
relays are mounted externally, but turned on and off
by the PCM through the same circuit. The camshaft position sensor and crankshaft posi-
tion sensor signals are sent to the PCM. If the PCM
does not receive both signals within approximately
one second of engine cranking, it deactivates the
ASD relay and fuel pump relay. When these relays
are deactivated, power is shut off to the fuel injector,
ignition coil, oxygen sensor heating element and fuel
pump. The PCM contains a voltage converter that
changes battery voltage to a regulated 8.0 volts. The
8.0 volts power the camshaft position sensor, crank- shaft position sensor and vehicle speed sensor. The
PCM also provides a 5.0 volts supply for the coolant
temperature sensor, manifold absolute pressure sen-
sor and throttle position sensor.
AIR CONDITIONING SWITCH SENSEÐPCM INPUT
When the air conditioning or defrost switch is put
in the ON position and the low pressure and high
pressure switches are closed, the PCM receives an in-
put for air conditioning. After receiving this input,
the PCM activates the A/C compressor clutch by
grounding the A/C clutch relay. The PCM also ad-
justs idle speed to a scheduled RPM to compensate
for increased engine load.
BATTERY VOLTAGEÐPCM INPUT
The PCM monitors the battery voltage input to de-
termine fuel injector pulse width and generator field
control. If battery voltage is low the PCM will in-
crease injector pulse width (period of time that the
injector is energized).
BRAKE SWITCHÐPCM INPUT
When the brake switch is activated, the PCM re-
ceives an input indicating that the brakes are being
applied. After receiving this input, the PCM vents
the speed control servo. Venting the servo turns the
speed control system off. The brake switch is
mounted on the brake pedal support bracket.
CAMSHAFT POSITION SENSORÐPCM INPUT
Fuel injection synchronization and cylinder identi-
fication are provided through the camshaft position
sensor (Fig. 3). The sensor generates pulses. The
pulse are the input sent to the PCM. The PCM inter-
prets the camshaft position sensor input along with
the crankshaft position sensor input to determine
crankshaft position. The PCM uses crankshaft posi-
tion sensor input to determine injector sequence and
ignition timing.
Fig. 3 Camshaft Sensor
Ä FUEL SYSTEMS 14 - 85

The camshaft position sensor senses when a notch in
the camshaft gear passes beneath it (Fig. 4). When
metal aligns with the sensor, voltage goes low (less
than 0.3 volts). When a notch aligns with the sensor,
voltage spikes 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 events. Top dead center (TDC) does not occur when notches
on the camshaft sprocket pass below the cylinder. TDC
occurs after the camshaft pulse (or pulses) and after
the 4 crankshaft pulses associated with the particular
cylinder.
The camshaft position sensor is mounted on the top
of the cylinder head (Fig. 5). The bottom of the sensor
is positioned above the camshaft sprocket. The dis-
tance between the bottom of sensor and the
camshaft sprocket is critical to the operation of
the system. When servicing the camshaft posi-
tion sensor, refer to the 2.2L Turbo III Multi-Port
Fuel InjectionÐService Procedures section in
this Group.
CHARGE AIR TEMPERATURE SENSORÐPCM IN-
PUT
The charge air temperature sensor is mounted to
intake manifold. The sensor measures the temperature
of the air-fuel mixture (Fig. 6). This information is used
by the PCM to modify air/fuel mixture and turbo-
charger boost level.
ENGINE COOLANT TEMPERATURE SENSORÐPCM
INPUT
The coolant temperature sensor is a variable resis-
tor with a range of -40ÉC to 128ÉF (-40ÉF to 265ÉF).
The sensor is installed into the thermostat housing
(Fig. 7). The PCM supplies 5.0 volts to the coolant temper-
ature sensor. The sensor provides an input voltage to
the PCM. The PCM determines engine operating
temperature from this input. As coolant temperature
varies, the sensor resistance changes resulting in a
different input voltage to the PCM. Based on the coolant sensor and charge air temper-
ature sensor inputs the PCM changes certain operat-
ing schedules until the engine reaches operating
temperature. While the engine warms up, the PCM
demands slightly richer air-fuel mixtures, lower
boost levels, revised spark advance and higher idle
speeds.
Fig. 5 Camshaft Position Sensor Location
Fig. 6 Charge Air Temperature Sensor
Fig. 4 Camshaft Gear
14 - 86 FUEL SYSTEMS Ä

CRANKSHAFT POSITION SENSORÐPCM INPUT
The crankshaft position sensor (Fig. 8) senses slots
cut into the flywheel. There ar e a 2 sets of slots.
Each set contains 4 slots, for a total of 8 slots (Fig.
9). Basic timing is set by the position of the last slot
in each group. Once the PCM senses the last slot, it
determines crankshaft position (which piston will
next be at TDC) from the camshaft position sensor
input. The 4 pulses generated by the crankshaft po-
sition sensor represent the 69É, 49É, 29É, and 9É BTDC
marks. It may take the PCM one engine revolution
to determine crankshaft position. The Turbo III en-
gine uses a fixed ignition system. Base timing is not
adjustable.
The PCM uses the crankshaft position sensor input
to determine injector sequence and ignition timing.
Once crankshaft position has been determined, the
PCM begins energizing the injectors in sequence. The crankshaft position sensor is located in the
transaxle housing, below the throttle body (Fig. 10).
The bottom of the sensor is positioned next to the
drive plate. The distance between the bottom of sensor and the drive plate is critical to the oper-
ation of the system. When servicing the crank-
shaft position sensor, refer to the 2.2L Turbo III
Multi-Port Fuel InjectionÐService Procedures
section in this Group.
KNOCK SENSORÐPCM INPUT
The knock sensor generates a signal when spark
knock occurs in the combustion chambers. The sensor
can detect detonation in the cylinders. The sensor
provides information used by the PCM to modify
spark advance and boost schedules in order to elimi-
nate detonation. The knock sensor is installed into the engine, be-
hind the PCV breather/separator (Fig. 11).
MANIFOLD ABSOLUTE PRESSURE (MAP)
SENSORÐPCM INPUT
The PCM supplies 5 volts to the MAP sensor. The
Map sensor converts intake manifold pressure into
voltage. The PCM monitors the MAP sensor output
voltage. As vacuum increases, MAP sensor voltage
decreases proportionately. Also, as vacuum decreases,
MAP sensor voltage increases proportionately.
Fig. 7 Coolant Temperature Sensor
Fig. 8 Crankshaft Position Sensor
Fig. 9 Timing Slots
Fig. 10 Crankshaft Position Sensor Location
Ä FUEL SYSTEMS 14 - 87

sition, the PCM monitors the crankshaft position and
camshaft position sensor signals to determine engine
speed and ignition timing (coil dwell). If the PCM
does not receive the crankshaft position sensor and
camshaft position sensor signals when the ignition
switch is in the Run position, it de-energizes both re-
lays. When the relays are de-energized, battery volt-
age is not supplied to the fuel injector, ignition coil,
fuel pump and oxygen sensor heating element. The ASD relay and fuel pump relay are located in
the power distribution center (Fig. 16).
IDLE AIR CONTROL MOTORÐPCM OUTPUT
The idle air control motor is mounted on the throt-
tle body (Fig. 14). The PCM operates the motor. The
PCM adjusts engine idle speed through the idle air
control motor to compensate for engine load or ambi-
ent conditions. The throttle body has an air bypass passage that
provides air for the engine at idle (the throttle blade
is closed). The idle air control motor pintle protrudes
into the air bypass passage and regulates air flow
through it. The PCM adjusts engine idle speed by moving the
idle air control motor pintle in and out of the bypass
passage. The adjustments are based on inputs the
PCM receives. The inputs are from the throttle posi-
tion sensor, camshaft position sensor, crankshaft po-
sition sensor, coolant temperature sensor, and
various switch operations (brake and air condition-
ing). Deceleration die out is also prevented by in-
creasing airflow when the throttle is closed quickly
after a driving (speed) condition.
BAROMETRIC READ SOLENOIDÐPCM OUTPUT
The barometric pressure read solenoid is spliced
into the manifold absolute pressure (MAP) sensor
vacuum hose (Fig. 12). The barometric read solenoid
switches the pressure supply to the MAP sensor from
either barometric pressure (atmospheric) or manifold
vacuum. The PCM operates the solenoid. Atmospheric pressure is periodically supplied to
the MAP sensor to measure barometric pressure.
This occurs at closed throttle, once per throttle clo-
sure but no more often than once every 3 minutes
and within a specified RPM band. Barometric infor-
mation is used primarily for boost control and start
fuel enrichment at various altitudes.
CANISTER PURGE SOLENOIDÐPCM OUTPUT
Vacuum for the Evaporative Canister is controlled
by the Canister Purge Solenoid (Fig. 17). The sole-
noid is controlled by the PCM. The PCM operates the solenoid by switching the
ground circuit on and off. When grounded, the sole-
noid energizes and prevents vacuum from reaching
the evaporative canister. When not energized the so-
lenoid allows vacuum to flow to the canister. During warm-up and for a specified time period after
hot starts the PCM grounds the purge solenoid.
Vacuum does not operate the evaporative canister
valve. The PCM removes the ground to the solenoid when
the engine reaches a specified temperature and the
time delay interval has occurred. When the solenoid is
de-energized, vacuum flows to the canister purge
valve. Vapors are purged from the canister and flow to
the throttle body. The purge solenoid will also be energized during
certain idle conditions, in order to update the fuel
delivery calibration.
MALFUNCTION INDICATOR LAMP (CHECK
ENGINE)ÐPCM OUTPUT
The malfunction indicator lamp (instrument panel
Check Engine lamp) comes on each time the ignition
key is turned ON and stays on for 3 seconds as a bulb
test. The malfunction indicator lamp warns the opera-
tor that the PCM has entered a Limp-in mode. During
Limp-in-Mode, the PCM attempts to keep the system
operational. The malfunction indicator lamp signals
the need for immediate service. In limp-in mode, the
PCM compensates for the failure of certain components
that send incorrect signals. The PCM substitutes for
the incorrect signals with inputs from other sensors. Signals that can trigger the malfunction indi-
cator lamp (Check Engine Lamp).
² Engine Coolant Temperature Sensor
² Manifold Absolute Pressure Sensor
² Throttle Position Sensor
² Battery Voltage Input
² An Emissions Related System
² Charging system
The malfunction indicator lamp can also be used to
display diagnostic trouble codes. Cycle the ignition
switch on, off, on, off, on, within five seconds and any
Fig. 17 EVAP Canister Purge Solenoid and Waste- gate Control Solenoid
14 - 90 FUEL SYSTEMS Ä

diagnostic trouble codes stored in the PCM will be
displayed. Refer to the 2.2L Turbo III Multi-port Fuel
InjectionÐOn-Board Diagnostics section of this
Group for Diagnostic trouble code Descriptions.
DATA LINK CONNECTORÐPCM OUTPUT
The data link connector provides the technician
with the means to connect the DRBII scan tool to di-
agnosis the vehicle.
FUEL INJECTORÐPCM OUTPUT
The Fuel Injectors are electric solenoids driven by
the PCM (Fig. 18).
Based on sensor inputs, the PCM determines when
and how long the fuel injector should operate. The
amount of time an injector fires is referred to as in-
jector pulse width. The auto shutdown (ASD) relay
supplies battery voltage to the injector. The PCM
supplies the ground path. By switching the ground
path on and off, the PCM adjusts injector pulse
width. When the PCM supplies a ground path, a spring
loaded needle or armature lifts from its seat and fuel
flows through the injector orifice. Fuel is constantly supplied to the injector at regu-
lated 380 Kpa (55 psi). Unused fuel returns to the
fuel tank.
IGNITION COILÐPCM OUTPUT
The Direct Ignition System (DIS) uses a molded
coil (Fig. 19). The coil is mounted on the front of the
engine. High tension leads route to each cylinder
from the coil. The coil fires two spark plugs every
power stroke. One plug is the cylinder under com-
pression, the other cylinder fires on the exhaust
stroke. The PCM determines which of the coils to
charge and fire at the correct time. The auto shutdown (ASD) relay provides battery
voltage to the ignition coil. The PCM provides a
ground contact (circuit) for energizing the coil. When the PCM breaks the contact, the energy in the coil
primary transfers to the secondary causing the
spark. The PCM will de-energize the ASD relay if it
does not receive the crankshaft position sensor and
camshaft position sensor inputs. Refer to Auto Shut-
down (ASD) Relay/Fuel Pump RelayÐPCM Output
in this section for relay operation.
RADIATOR FAN RELAYÐPCM OUTPUT
The radiator fan is energized by the PCM through
the radiator fan relay. The PCM grounds the radia-
tor fan relay when engine coolant reaches a predeter-
mined temperature. For more information, refer to
Group 7, Cooling Systems. The radiator fan relay is located in the power dis-
tribution center (Fig. 16). Refer to the Wiring and
Component Identification section of Group 8W.
SPEED CONTROL SOLENOIDSÐPCM 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.
TACHOMETERÐPCM OUTPUT
The PCM supplies engine RPM to the instrument
panel tachometer. Refer to Group 8 for tachometer
information.
WASTEGATE CONTROL SOLENOIDÐPCM OUTPUT
The PCM operates the wastegate control solenoid.
The PCM adjusts maximum boost to varying engine
conditions by changing the amount of time the sole-
Fig. 18 Fuel Injector
Fig. 19 Ignition Coil
Ä FUEL SYSTEMS 14 - 91

noid is energized. The solenoid mounts to the passen-
ger side inner fender panel, next to the strut tower
(Fig. 17).
MODES OF OPERATION
As input signals to the PCM change, the PCM
adjusts its response to the output devices. For example,
the PCM must calculate a different injector pulse
width and ignition timing for idle than it does 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 input
signals and responds according to preset PCM pro-
gramming. Input from the oxygen (O
2) sensor is not
monitored during OPEN LOOP modes. During CLOSED LOOP modes, the PCM does moni-
tor the oxygen (O
2) sensor input. This input indicates
to the PCM whether or not the calculated injector pulse
width results in the ideal air-fuel ratio of 14.7 parts air
to 1 part fuel. By monitoring the exhaust oxygen
content through the O
2sensor, the PCM can fine tune
the injector pulse width to achieve optimum fuel
economy combined with low emissions. The 2.2L Turbo III multi-port fuel injection system
has the following modes of operation:
² Ignition switch ON - Zero RPM
² Engine start-up
² Engine warm-up
² Cruise (Idle)
² Acceleration
² Deceleration
² Wide Open Throttle
² Ignition switch OFF
The engine start-up (crank), engine warm-up, and
wide open throttle modes are OPEN LOOP modes. The
acceleration, deceleration, and cruise modes, with the
engine at operating temperature are CLOSED
LOOP modes (under most operating conditions).
IGNITION SWITCH ON (ZERO RPM) MODE
When the ignition switch activates the fuel injection
system the following actions occur:
²
The PCM calculates basic fuel strategy by determining
atmospheric air pressure from the MAP sensor input.
² The PCM monitors the coolant temperature sensor
and throttle position sensor input. The PCM modifies
fuel strategy based on this input. When the key is in the ON position and the engine is
not running, the auto shutdown (ASD) relay and fuel
pump relay are not energized. Therefore battery volt-
age is not supplied to the fuel pump, ignition coil, fuel
injector or oxygen sensor heating element.
ENGINE START-UP MODE
This is an OPEN LOOP mode. The following actions
occur when the starter motor is engaged. If the PCM receives the camshaft position and crank-
shaft position sensor signals, it energizes the auto
shutdown (ASD) relay and fuel pump relay. These
relays supply battery voltage to the fuel pump, fuel
injectors, ignition coil, and oxygen sensor heating ele-
ment. If the PCM does not receive the camshaft posi-
tion sensor and crankshaft position sensor signals
within approximately one second, it de-energizes the
ASD relay and fuel pump relay. The PCM energizes all injectors until it determines
crankshaft position from the camshaft position sensor
and crankshaft position sensor signals. The PCM de-
termines crankshaft position within 1 engine revolu-
tion. After determining crankshaft position, the PCM be-
gins energizing the injectors in sequence. The PCM
adjusts injector pulse width and controls injector syn-
chronization by turning the individual ground paths to
the injectors On and Off. When the engine idles within 664 RPM of its target
RPM, the PCM compares current MAP sensor value
with the atmospheric pressure value received during
the Ignition Switch On (zero RPM) mode. If the PCM
does not detect a minimum difference between the two
values, it sets a MAP fault into memory. Once the ASD and fuel pump relays have been
energized, the PCM:
² Determines injector pulse width based on coolant
temperature, manifold absolute pressure (MAP) and
the number of engine revolutions since cranking was
initiated.
² Monitors the coolant temperature sensor, camshaft
position sensor, crankshaft position sensor, MAP sen-
sor, and throttle position sensor to determine correct
ignition timing.
ENGINE WARM-UP MODE
This is a OPEN LOOP mode. The following inputs
are received by the PCM:
² engine coolant temperature
² knock sensor
² manifold absolute pressure (MAP)
² engine speed (crankshaft position sensor)
² throttle position
² A/C switch
² battery voltage
The PCM provides a ground path for the injectors to
precisely control injector pulse width (by switching the
ground on and off). The PCM adjusts engine idle speed
through the idle air control motor. Also, the PCM
regulates ignition timing.
14 - 92 FUEL SYSTEMS Ä

CRUISE OR IDLE MODE
When the engine is at operating temperature, this is
a CLOSED LOOP mode. During cruising speed the
following inputs are received by the PCM:
² engine coolant temperature
² knock sensor
² manifold absolute pressure
² engine speed (crankshaft position sensor)
² throttle position
² exhaust gas oxygen content
² A/C control positions
² battery voltage
The PCM provides a ground path for the injectors to
precisely control injector pulse width. The PCM adjusts
engine idle speed and ignition timing. The PCM con-
trols the air/fuel ratio according to the oxygen content
in the exhaust gas.
ACCELERATION MODE
This is a CLOSED LOOP mode. The PCM recognizes
an abrupt increase in throttle position or MAP pres-
sure as a demand for increased engine output and
vehicle acceleration. The PCM increases injector pulse
width in response to increased fuel demand.
DECELERATION MODE
This is a CLOSED LOOP mode. During deceleration
the following inputs are received by the PCM:
² engine coolant temperature
² knock sensor
² manifold absolute pressure
² engine speed (crankshaft position sensor)
² throttle position
² exhaust gas oxygen content ²
A/C control positions
² battery voltage
The PCM may receive a closed throttle input from
the throttle position sensor (TPS) at the same time it
senses an abrupt decrease in manifold pressure. This
indicates a hard deceleration. The PCM modifies the
injector sequence. This helps maintain better control
of the air-fuel mixture.
WIDE OPEN THROTTLE MODE
This is an OPEN LOOP mode. During wide-open-
throttle operation, the following inputs are received
by the PCM:
² engine coolant temperature
² knock sensor
² manifold absolute pressure
² engine speed (crankshaft position sensor)
² throttle position
When the PCM senses a wide open throttle condi-
tion it will de-energize the air conditioning relay.
This disables the air conditioning system. The exhaust gas oxygen content input is not ac-
cepted by the PCM during wide open throttle opera-
tion. The PCM will enrichen the air/fuel ratio to
increase performance and compensate for increased
combustion chamber temperature.
IGNITION SWITCH OFF MODE
This is an OPEN LOOP mode. When the ignition
switch is turned to the OFF position, the following
occurs:
² All outputs are turned off.
² No inputs are monitored.
² The PCM shuts down.
Fig. 20 Throttle Body
Ä FUEL SYSTEMS 14 - 93