1993 CHEVROLET DYNASTY engine

SPEED CONTROLÐPCM INPUT
The speed control system provides four separate
voltages (inputs) to the PCM. The voltages corre-
spond to the On/Off, Set, and Resume. The speed control ON voltage informs the PCM
that the speed control system has been activated.
The speed control SET voltage informs the PCM that
a fixed vehicle speed has been selected. The speed
control RESUME voltage indicates the previous fixed
speed is requested. The speed control OFF voltage
tells the PCM that the speed control system has been
deactivated. Refer to Group 8H for further speed con-
trol information.
TRANSAXLE PARK/NEUTRAL SWITCHÐPCM
INPUT
The park/neutral switch is located on the transaxle
housing (Fig. 12). It provides an input to the PCM
indicating whether the automatic transaxle is in
Park or Neutral. This input is used to determine idle
speed (varying with gear selection) and ignition tim-
ing advance. The park neutral switch is sometimes
referred to as the neutral safety switch.
THROTTLE POSITION SENSOR (TPS)ÐPCM INPUT
The Throttle Position Sensor (TPS) is mounted on
the throttle body and connected to the throttle blade
shaft (Fig. 13). The TPS is a variable resistor that
provides the PCM with an input signal (voltage). The
signal represents throttle blade position. As the posi-
tion of the throttle blade changes, the resistance of
the TPS changes. The PCM supplies approximately 5 volts to the
TPS. The TPS output voltage (input signal to the
PCM) represents the throttle blade position. The TPS
output voltage to the PCM varies from approxi-
mately 0.5 volt at minimum throttle opening (idle) to
3.5 volts at wide open throttle. Along with inputs
from other sensors, the PCM uses the TPS input to
determine current engine operating conditions. The PCM also adjust fuel injector pulse width and igni-
tion timing based on these inputs.
VEHICLE SPEED AND DISTANCE INPUTÐPCM
INPUT
The transaxle output speed sensor supplies the ve-
hicle speed and distance inputs to the PCM. The out-
put speed sensor is located on the side of the
transaxle (Fig. 12). The speed and distance signals, along with a closed
throttle signal from the TPS, determine if a closed
throttle deceleration or normal idle condition (vehicle
stopped) exists. Under deceleration conditions, the
PCM adjusts the idle air control motor to maintain a
desired MAP value. Under idle conditions, the PCM
adjusts the idle air control motor to maintain a de-
sired engine speed.
AIR CONDITIONING (A/C) CLUTCH RELAYÐPCM
OUTPUT
The PCM operates the air conditioning clutch relay
ground circuit (Fig. 14). The ignition switch supplies
battery voltage to the solenoid side of the relay.
When the A/C clutch relay energizes, battery voltage
powers the A/C compressor clutch. With the engine operating and the blower motor
switch in the On position, the PCM cycles the air
conditioning clutch on and off when the A/C switch
closes. When the PCM senses low idle speeds or wide
open throttle through the throttle position sensor, it
de-energizes the A/C clutch relay. The relay contacts
open, preventing air conditioning clutch engagement.
GENERATOR FIELDÐPCM OUTPUT
The PCM regulates the charging system voltage
Fig. 13 Throttle Position Sensor
Fig. 12 Park Neutral SwitchÐ4-Speed Electronic Automatic Transaxle
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within a range of 12.9 to 15.0 volts. Refer to Group
8A for charging system information.
AUTO SHUTDOWN (ASD) RELAY AND FUEL PUMP
RELAYÐPCM OUTPUT
The PCM operates the auto shutdown (ASD) relay
and fuel pump relay through one ground path. The
PCM operates the relays by switching the ground
path on and off. Both relays turn on and off at the
same time. The ASD relay connects battery voltage to the fuel
injector and ignition coil. The fuel pump relay con-
nects battery voltage to the fuel pump and oxygen
sensor heating element. The PCM turns the ground path off when the igni-
tion switch is in the Off position. Both relays are off.
When the ignition switch is in the On or Crank po-
sition, the PCM monitors the crankshaft position
sensor and camshaft position sensor signals to deter-
mine 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 relays. When the relays are de-energized, bat-
tery voltage is not supplied to the fuel injector, igni-
tion coil, fuel pump and oxygen sensor heating
element. The ASD relay and fuel pump relay are located in
the power distribution center (Fig. 14).
IDLE AIR CONTROL MOTORÐPCM OUTPUT
The idle air control motor is mounted on the throt-
tle body. The PCM operates the idle air control motor
(Fig. 13). The PCM adjusts engine idle speed through
the idle air control motor to compensate for engine
load or ambient 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, crankshaft position sensor, coolant tem-
perature sensor, and various switch operations
(brake, park/neutral, air conditioning). Deceleration
die out is also prevented by increasing airflow when
the throttle is closed quickly after a driving (speed)
condition.
CANISTER PURGE SOLENOIDÐPCM OUTPUT
Vacuum for the Evaporative Canister is controlled
by the Canister Purge Solenoid (Fig. 15). The sole-
noid is controlled by the PCM.
The PCM operates the solenoid by switching the
ground circuit on and off based on engine operating
conditions. When energized, the solenoid prevents
vacuum from reaching the evaporative canister.
When not energized the solenoid allows vacuum to
flow to the canister. 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 de-
livery calibration.
MALFUNCTION INDICATOR LAMP (CHECK ENGINE
LAMP)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
Fig. 14 Relay Identification
Fig. 15 Canister Purge Solenoid
Ä FUEL SYSTEMS 14 - 151

operator that the PCM has entered a Limp-in mode.
During Limp-in Mode, the PCM attempts to keep the
system operational. The malfunction indicator 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 Emission Related System (California vehicles)
² Charging system
The malfunction indicator (Check Engine Lamp) can
also display diagnostic trouble codes. Cycle the ignition
switch on, off, on, off, on, within five seconds and any
diagnostic trouble codes stored in the PCM will be
displayed. Refer to the 3.3L and 3.8L 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 diagnosis
the vehicle.
TRANSAXLE CONTROL MODULEÐPCM OUTPUT
The PCM supplies the following information to the
electronic automatic transaxle control module through
the CCD Bus:
² battery temperature
² brake switch input
² engine coolant temperature
² manifold absolute pressure (MAP)
² speed control information
ELECTRIC EGR TRANSDUCER (EET)
SOLENOIDÐPCM OUTPUT
The electronic EGR transducer (EET) contains an
electrically operated solenoid and a back-pressure
transducer (Fig. 16). The PCM operates the solenoid.
The PCM determines when to energize the solenoid.
Exhaust system back-pressure controls the transducer. When the PCM energizes the solenoid, vacuum does
not reach the EGR valve. Vacuum flows to the EGR
valve when the PCM de-energizes the solenoid. When exhaust system back-pressure becomes high
enough, it fully closes a bleed valve in the transducer.
When the PCM de-energizes the solenoid and back-
pressure closes the transducer bleed valve, vacuum
flows through the transducer to operate the EGR valve. De-energizing the solenoid, but not fully closing the
transducer bleed hole (because of by low back- pressure), varies the strength of vacuum applied to
the EGR valve. Varying the strength of the vacuum
changes the amount of EGR supplied to the engine.
This provides the correct amount of exhaust gas re-
circulation for different operating conditions.
FUEL INJECTORSÐPCM OUTPUT
The fuel injectors are electrical solenoids (Fig. 17).
The injector contains a pintle that closes off an ori-
fice at the nozzle end. When electric current is sup-
plied to the injector, the armature and needle move a
short distance against a spring, allowing fuel to flow
out the orifice. Because the fuel is under high pres-
sure, a fine spray is developed in the shape of a hol-
low cone. The spraying action atomizes the fuel,
adding it to the air entering the combustion cham-
ber. The injectors are positioned in the intake mani-
fold.
The fuel injectors are operated by the PCM. They
are energized in a sequential order during all engine
operating conditions except start up. The PCM ini-
tially energizes all injectors at the same time. Once
Fig. 16 Electric EGR Transducer (EET) Assembly
Fig. 17 Fuel InjectorÐ3.3L Engine
14 - 152 FUEL SYSTEMS Ä

the PCM determines crankshaft position, it begins
energizing the injectors in sequence.The auto shutdown (ASD) relay supplies battery
voltage to the injectors. 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 inputs it receives.
IGNITION COILÐPCM OUTPUT
The coil assembly consists of 3 molded coils to-
gether (Fig. 18). The coil assembly is mounted on the
intake manifold. 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
compression, 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 radiator fan relay is lo-
cated on the drivers side fender well near the PCM
(Fig. 14). The PCM grounds the radiator fan relay
when engine coolant reaches a predetermined tem-
perature or the A/C system head pressure is high.
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 sole-
noids 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
adjusts its response to 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 monitor
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. Fine tuning injector pulse
width allows the PCM to achieve optimum fuel
economy combined with low emissions. The 3.3L 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.
Under most operating conditions, the acceleration,
deceleration, and cruise modes, with the engine at
operating temperature are CLOSED LOOP modes.
Fig. 18 Coil PackÐ3.3L Engine
Ä FUEL SYSTEMS 14 - 153

IGNITION SWITCH ON (ZERO RPM) MODE When the multi-port fuel injection system is acti-
vated by the ignition switch, the following actions oc-
cur:
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 this input. 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. There-
fore 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 ac-
tions occur when the starter motor is engaged. If the PCM receives the camshaft position sensor
and crankshaft 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 heat-
ing element. If the PCM does not receive the cam-
shaft position sensor and crankshaft position sensor
signals within approximately one second, it de-ener-
gizes the ASD relay and fuel pump relay. The PCM energizes all six injectors until it deter-
mines crankshaft position from the camshaft position
sensor and crankshaft position sensor signals. The
PCM determines crankshaft position within 1 engine
revolution. After determining crankshaft position, the PCM
begins 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 tar-
get 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 be-
tween the two values, it sets a MAP fault into mem-
ory. Once the ASD and fuel pump relays have been en-
ergized, the PCM:
² Determines injector pulse width based on battery
voltage, coolant temperature, engine rpm and the
number of engine revolutions since cranking was ini-
tiated.
ENGINE WARM-UP MODE This is a OPEN LOOP mode. The following inputs
are received by the PCM:
² engine coolant temperature ²
manifold absolute pressure (MAP)
² engine speed (crankshaft position sensor)
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 ignition timing and engine idle
speed. Engine idle speed is adjusted through the idle
air control motor.
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 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 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 adjusts 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 manifold absolute pressure
² engine speed
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) when it senses an
abrupt decrease in manifold pressure. This indicates
a hard deceleration. The PCM will reduce injector
pulse width. This helps maintain better control of the
air-fuel mixture (as sensed through the O
2sensor).
During a closed throttle deceleration condition, the
PCM grounds the exhaust gas recirculation (EGR)
solenoid. When the solenoid is grounded, EGR func-
tion stops.
14 - 154 FUEL SYSTEMS Ä

WIDE OPEN THROTTLE MODE This is an OPEN LOOP mode. During wide-open-
throttle operation, the following inputs are received
by the PCM:
² battery voltage
² engine coolant temperature
² manifold absolute pressure
² engine speed
² throttle position
When the PCM senses wide open throttle condition
through the throttle position sensor (TPS) it will:
² De-energize the air conditioning relay. This dis-
ables the air conditioning system.
² Provide a ground for the electrical EGR transducer
(EET) solenoid. When the PCM grounds the solenoid,
the EGR system stops operating. 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 is located on the left
side of the intake manifold plenum (Fig. 19). The
throttle body houses the throttle position sensor and
the idle air control motor. Air flow through the throt- tle body is controlled by a cable operated throttle
blade located in the base of the throttle body.
FUEL SUPPLY CIRCUIT
Fuel is pumped to the fuel rail by an electrical
pump in the fuel tank. The pump inlet is fitted with
a strainer to prevent water and other contaminants
from entering the fuel supply circuit. Fuel pressure is controlled to a preset level above
intake manifold pressure by a pressure regulator.
The regulator is mounted on the fuel rail. The regu-
lator uses intake manifold pressure as a reference.
FUEL INJECTORS AND FUEL RAIL ASSEMBLY
Six fuel injectors are retained in the fuel rail by
lock rings (Fig. 20). The rail and injector assembly is
installed in position with the injectors inserted in re-
cessed holes in the intake manifold.
Fig. 19 Throttle Body
Fig. 20 Fuel Rail Assembly
Ä FUEL SYSTEMS 14 - 155

3.3L AND 3.8L MULTI-PORT FUEL INJECTIONÐGENERAL DIAGNOSIS INDEX
page page
Fuel System Diagram .................... 157 Visual Inspection........................ 157
FUEL SYSTEM DIAGRAM
Refer to the Component Identification portion of
this section for a more complete description of the
components shown in Fig. 1.
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 ignition cable routing from the coil pack
to the spark plugs. Verify the cable are routed in the
correct order and are fully seated to the coil and
spark plug. (2) Check direct ignition system (DIS) coil electri-
cal connection for damage and a complete connection
to the coil (Fig. 2). (3) Verify the camshaft position sensor electrical
connector is connected to the harness and not dam-
aged (Fig. 3). (4) Ensure the engine temperature sensor electri-
cal connector is connected to the sensor and not dam-
aged (Fig. 3). (5) Ensure the coolant temperature sensor electri-
cal connector is connected to the sensor and not dam-
aged (Fig. 4). (6) Verify the quick connect fuel fittings are fully
inserted on the fuel supply and return tubes. (7) Check the vacuum hose connection at the fuel
pressure regulator for damage or leakage (Fig. 5). (8) Check the oil pressure sending unit electrical
connection (Fig. 6). (9) Verify the electrical connector is attached to
the Purge Solenoid (Fig. 7) and not damaged. (10) Verify the vacuum connection at the purge so-
lenoid is secure and not leaking (Fig. 7).
Fig. 1 Multi-Port Fuel Injection Components
Ä FUEL SYSTEMS 14 - 157

(11) Verify the hoses are securely attached to the
vapor canister (Fig. 8). (12) Ensure the harness connectors for the fuel in-
jector are attached to the correct injector and not
damaged. (13) Verify the fuel injector harness and engine
wiring harness connectors are fully inserted into the
main wiring harness. (14) Check the vacuum connections at the throttle
body (Fig. 9). (15) Ensure the idle air control motor and TPS
electrical connectors are fully seated and not dam-
aged (Fig. 9). (16) Verify the harness connector is attached to
the electric EGR transducer solenoid (Fig. 9). (17) Verify the vacuum connections at the trans-
ducer are secure (Fig. 9). Check all EGR system vac-
uum hoses for secure connections. Inspect the EGR
tube.
Fig. 2 Ignition Coils Electrical Connection
Fig. 3 Camshaft Position Sensor
Fig. 4 Engine Coolant Temperature Sensor
Fig. 5 Fuel Pressure Regulator Vacuum Connection
Fig. 6 Oil Pressure Sending Unit Electrical Connection
14 - 158 FUEL SYSTEMS Ä