CHEVROLET PLYMOUTH ACCLAIM 1993 Service Manual

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 COILÐPCM 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-
layÐPCM 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 SOLENOIDÐPCM
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 RELAYÐPCM 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 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 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
2sensor, 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:
² Ignition switch ONÐZero-RPM
² Engine start-up
² Engine warm-up
² Cruise (Idle)
² Acceleration
² Deceleration
² Wide Open Throttle
² Ignition switch OFF
Fig. 18 Ignition Coil
Ä FUEL SYSTEMS 14 - 121

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 multi-port fuel injection system is acti-
vated by the ignition switch, the following actions
occur:
² The PCM determines atmospheric air pressure from
the MAP sensor input to determine basic fuel strategy.
² The PCM monitors the coolant temperature sensor
and throttle position sensor input. The PCM modifies
fuel strategy based on these inputs. When the key is in the ON position and the engine is
not running (zero rpm), the auto shutdown (ASD) relay
and fuel pump relay are not energized. Therefore
battery voltage is not supplied to the fuel pump,
ignition coil, fuel injectors 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 a distributor signal, 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
element. If the PCM does not receive a distributor
input, the ASD relay and fuel pump relay will be
de-energized after approximately one second. The PCM energizes all six injectors until it deter-
mines crankshaft position from the distributor pick-up
signals. The PCM determines crankshaft position
within 2 engine revolutions. 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, distribu-
tor pick-up, MAP sensor, 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 crankshaft position (distributor pick-up)
² manifold absolute pressure (MAP)
² engine speed (distributor pick-up)
² throttle position
² A/C switch
² battery voltage
The PCM adjusts injector pulse width and controls
injector synchronization by turning the individual
ground paths to the injectors On and Off. The PCM adjusts engine idle speed by regulating
the idle air control motor and ignition timing.
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 crankshaft position (distributor pick-up)
² manifold absolute pressure
² engine speed (distributor pick-up)
² throttle position
² exhaust gas oxygen content
² A/C control positions
² battery voltage
The PCM adjusts injector pulse width and controls
injector synchronization by turning the individual
ground paths to the injectors On and Off. The PCM adjusts engine idle speed and ignition
timing. The PCM controls the air/fuel ratio according
to the oxygen content in the exhaust gas.
ACCELERATION MODE This is a CLOSED LOOP mode. The PCM recog-
nizes an abrupt increase in throttle position or MAP
pressure 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 decelera-
tion the following inputs are received by the PCM:
² engine coolant temperature
² crankshaft position (distributor pick-up)
² manifold absolute pressure
² engine speed (distributor pick-up)
² throttle position
² exhaust gas oxygen content
² A/C control positions
² battery voltage
14 - 122 FUEL SYSTEMS Ä

The PCM may receive a closed throttle input from
the throttle position sensor (TPS) when it senses an
abrupt decrease in manifold pressure. This indicates
a hard deceleration. The PCM may reduce injector
firing to once per engine revolution. This helps main-
tain better control of the air-fuel mixture. During a deceleration condition, the PCM grounds
the exhaust gas recirculation (EGR) solenoid. When
the PCM grounds the solenoid, preventing EGR.
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 crankshaft position (distributor pick-up)
² manifold absolute pressure
² engine speed (distributor pick-up)
² throttle position
When the PCM senses wide open throttle condition
through the throttle position sensor (TPS) it will:
² Provide a ground for the electrical EGR transducer
(EET) solenoid. When the PCM grounds the solenoid,
the EGR system stops operating.
² De-energize the air conditioning relay. This dis-
ables 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 adjust injector pulse width to
supply a predetermined amount of additional fuel.
IGNITION SWITCH OFF MODE
When the ignition switch is turned to the OFF po-
sition, the following occurs:
² All outputs are turned off.
² No inputs are monitored.
² The PCM shuts down.
THROTTLE BODY
The throttle body assembly (Fig. 19) is located at
the left end of the air intake plenum. The throttle
body houses the throttle position sensor and the idle
air control motor. Air flow through the throttle body
is controlled by a cable operated throttle blade lo-
cated in the base of the throttle body.
FUEL SUPPLY CIRCUIT
Fuel is supplied to the fuel rail by an electric pump
mounted in the fuel tank. The pump inlet is fitted
with a strainer to prevent water and other contami-
nants from entering the fuel supply circuit. Fuel pressure is controlled to a preset level above
intake manifold pressure by a pressure regulator.
The pressure regulator is mounted on the fuel rail.
The regulator uses intake manifold pressure as a ref-
erence.
Fig. 19 Throttle Body
Ä FUEL SYSTEMS 14 - 123

FUEL PRESSURE REGULATOR
The pressure regulator is a mechanical device lo-
cated on the fuel rail, downstream of the fuel injec-
tors (Fig. 20). The regulator maintains a constant
328 kPa (47.6 psi) across the fuel injector tip. The regulator contains a spring loaded rubber dia-
phragm that covers the fuel return port. When the
fuel pump is operating, fuel flows past the injectors
into the regulator. Fuel is restricted from flowing
any further by the blocked return port. When fuel
pressure reaches 328 kPa (47.6 psi) it pushes on the
diaphragm, compresses the spring, and uncovers the
fuel return port. The diaphragm and spring con-
stantly move from an open to closed position to keep
the fuel pressure constant.
Fig. 20 Fuel Pressure Regulator
14 - 124 FUEL SYSTEMS Ä

3.0L MULTI-PORT FUEL INJECTIONÐGENERAL DIAGNOSIS INDEX
page page
Fuel System Diagram .................... 125 Visual Inspection........................ 125
FUEL SYSTEM DIAGRAM
The 3.0L MPI system is managed by the PCM. The
PCM receives inputs from various switches and sen-
sors (Fig. 1). Based on these inputs, the PCM adjusts
ignition timing and idle speed through various out-
put devices. Refer to the Multi-Port Fuel Injec-
tionÐ3.0L Engine section of this group for system
and component descriptions.
VISUAL INSPECTION
Perform a visual inspection for loose, disconnected,
or misrouted wires and hoses before diagnosing or
servicing the fuel injection system. A visual check
saves unnecessary test and diagnostic time. A thor-
ough visual inspection includes the following checks: (1) Check for correct spark plug cable routing. En-
sure the cables are completely connected to the spark
plugs and distributor. (2) Check ignition coil electrical connections (Fig.
2). (3) Verify the electrical connector is attached to
the Purge Solenoid (Fig. 3).
Fig. 1 Multi-Port Fuel Injection Components
Fig. 2 Ignition Coil Electrical Connection
Ä FUEL SYSTEMS 14 - 125

(4) Verify vacuum connection at Purge Solenoid is
secure and not leaking (Fig. 3).
(5) Verify the electrical connector is attached to
the MAP sensor (Fig. 4). (6) Check MAP sensor hose at MAP Sensor Assem-
bly (Fig. 4), and at Vacuum Connection at Intake
Plenum Fitting.
(7) Check generator wiring connections. Ensure
the accessory drive belt has proper tension. (8) Verify hoses are securely attached to the vapor
canister (Fig. 5). (9) Verify the engine ground strap is attached at
the engine and dash panel (Fig. 6). (10) Ensure the heated oxygen sensor connector is
connected to the harness connector (Fig. 6). (11) Verify the distributor connector is connected
to the harness connector (Fig. 7). (12) Verify the coolant temperature sensor connec-
tor is connected to the harness connector (Fig. 8). (13) Check vacuum hose connection at fuel pres-
sure regulator and intake plenum connector (Fig. 8).
Fig. 3 Duty Cycle EVAP Canister Purge Solenoid
Fig. 4 Map Sensor Electrical and Vacuum Connections
Fig. 5 Vapor Canister
Fig. 6 Oxygen Sensor Connector
Fig. 7 Distributor Connector
14 - 126 FUEL SYSTEMS Ä

(14) Ensure the harness connector is securely at-
tached to each fuel injector. (15) Check the oil pressure sending unit electrical
connection (Fig. 9).
(16) Check hose connections at throttle body (Fig.
10). (17) Check throttle body electrical connections
(Fig. 10). (18) Check PCV hose connections (Fig. 11).
(19) If equipped, check EGR system vacuum hose
connections (Fig. 12). (20) If equipped, check EGR tube to intake plenum
connections (Fig. 12). (21) Inspect the electronic EGR transducer sole-
noid electrical connector. (22) Ensure the vacuum connections at the elec-
tronic EGR transducer is secure and not leaking.
Fig. 8 Coolant Temperature Sensor and Vacuum Connections
Fig. 9 Oil Pressure Sending Unit ElectricalConnection
Fig. 10 Throttle Body Electrical and Vacuum Hose Connections
Fig. 11 Positive Crankcase Ventilation (PCV) System
Fig. 12 EGR System Vacuum Hose Connections
Ä FUEL SYSTEMS 14 - 127

(23) Check Power Brake Booster and Speed Con-
nections (Figs. 13 and 14).
(24) Inspect engine harness to main harness con-
nections. (25) Check all automatic transaxle electrical con-
nections (Fig. 15). (26) Check the vehicle speed sensor electrical con-
nection (Fig. 16). (27) Inspect the PCM 60-way electrical connector
for damage or spread terminals. Verify the 60-way
connector is fully inserted into the socket of the
PCM. Ensure wires are not stretched or pulled out of
the connector (Figs. 17, 18, and 19).
Fig. 13 Power Brake Booster and Speed Control Vacuum Hose Connections (Without Anti-lock Brakes)
Fig. 14 Speed Control Vacuum Hose Connection(With Anti-lock Brakes)
Fig. 15 Automatic Transaxle Electrical Connections
Fig. 16 Vehicle Speed Sensor Electrical Connector
Fig. 17 PCMÐAA Body
14 - 128 FUEL SYSTEMS Ä

(28) Check the air conditioning, starter, ASD, fuel
pump and radiator fan relay connections (Figs. 20,
21, and 22).
(29) Check battery cable connections.
(30) Check hose and electrical connections at fuel
pump. Ensure connector is making contact with ter-
minals on pump.
Fig. 18 PCMÐAC Body
Fig. 19 PCMÐAG and AJ Bodies
Fig. 20 Relay IdentificationÐAA Body
Fig. 21 Relay IdentificationÐAC Body
Fig. 22 Relay IdentificationÐAG and AJ Bodies
Ä FUEL SYSTEMS 14 - 129

3.0L MULTI-PORT FUEL INJECTIONÐON-BOARD DIAGNOSTICS INDEX
page page
60-Way PCM Wiring Connector ............. 136
Circuit Actuation Test Mode ................ 134
Diagnostic Trouble Code Description ......... 131
General Information ...................... 130
High and Low Limits ..................... 131
Ignition Timing Procedure ................. 136 Monitored Circuits
....................... 130
Non-Monitored Circuits ................... 131
State Display Test Mode .................. 134
System Tests .......................... 134
Throttle Body Minimum Air Flow Check Procedure ............................ 135
GENERAL INFORMATION
The PCM has been programmed to monitor many
different circuits of the fuel injection system. If a
problem is sensed with a monitored circuit often
enough to indicate an actual problem, the PCM
stores a fault. If the problem is repaired or ceases to
exist, the PCM cancels the Diagnostic trouble code
after 51 vehicle key on/off cycles. Certain criteria must be met for a diagnostic trou-
ble code to be entered into PCM memory. The crite-
ria may be a specific range of engine RPM, engine
temperature, and/or input voltage to the PCM. It is possible a diagnostic trouble code for a moni-
tored circuit may not be entered into memory even
though a malfunction has occurred. This may happen
because one of the diagnostic trouble code criteria for
the circuit has not been met. For example, assume
one of the diagnostic trouble code criteria for a cer-
tain sensor is the engine must be operating between
750 and 2000 RPM. If the sensor output circuit
shorts to ground when engine RPM is above 2400
RPM (resulting i n a 0 volt input to the PCM) a diag-
nostic trouble code will not be entered into memory.
This is because the condition does not occur within
the specified RPM range. There are several operating conditions that the
PCM does not monitor and set diagnostic trouble
codes for. Refer to Monitored Circuits and Non-Mon-
itored Circuits in this section. Stored diagnostic trouble codes can be displayed ei-
ther by cycling the ignition key On - Off - On - Off -
On, or through use of the DRBII scan tool. The
DRBII scan tool connects to the data link connector
in the vehicle (Fig. 1, Fig. 2 or Fig. 3).
MONITORED CIRCUITS
The powertrain control module (PCM) can detect
certain fault conditions in the fuel injection system. Open or Shorted Circuit - The PCM can deter-
mine if the sensor output (input to PCM) is within
proper range. Also, the PCM can determine if the cir-
cuit is open or shorted. Output Device Current Flow - The PCM senses
whether the output devices are hooked up. If there is a problem with the circuit, the PCM senses whether
the circuit is open, shorted to ground, or shorted
high. Oxygen Sensor - The PCM can determine if the
oxygen sensor is switching between rich and lean
once the system has entered closed loop. Refer to
Modes of Operation in this section for an explanation
of closed loop operation.
Fig. 1 PCMÐAA Body
Fig. 2 PCMÐAC Body
14 - 130 FUEL SYSTEMS Ä