fuel CHEVROLET DYNASTY 1993 Service Manual

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

NON-MONITORED CIRCUITS
The PCM does not monitor the following circuits,
systems and conditions that could have malfunctions
that result in driveability problems. Diagnostic trouble
codes may not be displayed for these conditions. How-
ever, problems with these systems may cause diagnos-
tic trouble codes to be displayed for other systems. For
example, a fuel pressure problem will not register a
fault directly, but could cause a rich or lean condition.
This could cause an oxygen sensor fault to be stored in
the PCM. Fuel Pressure - Fuel pressure is controlled by the
vacuum assisted fuel pressure regulator. The PCM
cannot detect a clogged fuel pump inlet filter, clogged
in-line fuel filter, or a pinched fuel supply or return
line. However, these could result in a rich or lean
condition causing an oxygen sensor fault. Secondary Ignition Circuit - The PCM cannot
detect an inoperative ignition coil, fouled or worn spark
plugs, ignition cross firing, or open spark plug cables. Engine Timing - The PCM cannot detect an incor-
rectly indexed timing chain, camshaft sprocket and
crankshaft sprocket. The PCM also cannot detect an
incorrectly indexed distributor. However, these could
result in a rich or lean condition causing an oxygen
sensor fault to be stored in the PCM. Cylinder Compression - The PCM cannot detect
uneven, low, or high engine cylinder compression. Exhaust System - The PCM cannot detect a
plugged, restricted or leaking exhaust system. Fuel Injector Malfunctions
- The PCM cannot
determine if the fuel injector is clogged, the pintle is
sticking or the wrong injector is installed. However,
these could result in a rich or lean condition causing an
oxygen sensor fault to be stored in the PCM. Excessive Oil Consumption - Although the PCM
monitors exhaust stream oxygen content when the
system is in closed loop, it cannot determine excessive
oil consumption. Throttle Body Air Flow - The PCM cannot detect a
clogged or restricted air cleaner inlet or filter element. Evaporative System - The PCM will not detect a
restricted, plugged or loaded evaporative purge canis-
ter. Vacuum Assist - Leaks or restrictions in the
vacuum circuits of vacuum assisted engine control
system devices are not monitored by the PCM. How-
ever, these could result in a MAP sensor fault being
stored in the PCM. PCM System Ground - The PCM cannot determine
a poor system ground. However, a diagnostic trouble
code may be generated as a result of this condition. PCM Connector Engagement - The PCM cannot
determine spread or damaged connector pins. How-
ever, a diagnostic trouble code may be generated as a
result of this condition.
HIGH AND LOW LIMITS
The powertrain control module (PCM) compares in-
put signal voltages from each input device with estab-
lished high and low limits that are programmed into it
for that device. If the input voltage is not within
specifications, and other diagnostic trouble code crite-
ria are met, a diagnostic trouble code will be stored in
memory. Other diagnostic trouble code criteria might
include engine RPM limits or input voltages from other
sensors or switches that must be present before a fault
condition can be verified.
DIAGNOSTIC TROUBLE CODE DESCRIPTION
When a diagnostic trouble code appears, it indicates
that the Powertrain control module (PCM) has recog-
nized an abnormal condition in the system. Diagnostic
trouble codes can be obtained from the malfunction
indicator lamp (Check Engine lamp on the Instrument
Panel) or from the DRBII scan tool. Diagnostic trouble
codes indicate the results of a failure but do not
identify the failed component directly.
Fig. 3 PCMÐAG and AJ Bodies
Ä FUEL SYSTEMS 14 - 131