1993 CHEVROLET DYNASTY engine

The oxygen sensor contains a heating element that
keeps it at proper temperature during all operating
modes. Maintaining correct sensor temperature at all times allows the system to enter into closed loop op-
eration sooner and remain in closed loop during pe-
riods of extended idle.
In Closed Loop operation the powertrain control
module (PCM) monitors the O
2sensor input (along
with other inputs) and adjusts the injector pulse
width accordingly. During Open Loop operation the
PCM ignores the O
2sensor input. The PCM adjusts
injector pulse width based on preprogrammed (fixed)
oxygen sensor input values and the current inputs
from other sensors.
REMOVAL
CAUTION: Do not pull on the oxygen sensor wire
when disconnecting the electrical connector.
WARNING: THE EXHAUST MANIFOLD MAY BE EX-
TREMELY HOT. USE CARE WHEN SERVICING THE
OXYGEN SENSOR.
Fig. 6 Heated Oxygen SensorÐ2.5L Engine
Fig. 7 Heated Oxygen SensorÐ2.5L MPI Engine (Flexible Fuel AA-body)
Fig. 8 Heated Oxygen SensorÐTurbo III Engine
Fig. 9 Heated Oxygen SensorÐ3.0L Engine
Fig. 10 Heated Oxygen SensorÐ3.3L/3.8L Engine
Ä EMISSION CONTROL SYSTEMS 25 - 19

(1) Disconnect oxygen sensor electrical connector.
(2) Remove sensor using Tool C-4907 (Fig. 11).
After removing the sensor, the exhaust manifold
threads must be cleaned with an 18 mm X 1.5 + 6E
tap. If reusing the original sensor, coat the sensor
threads with an anti-seize compound such as Loctite
771-64 or equivalent. New sensors have compound on
the threads and do not require additional compound.
Tighten the sensor to 27 N Im (20 ft. lbs.) torque.
EXHAUST GAS RECIRCULATION (EGR) SYSTEM
Certain vehicles equipped with either a 2.2L, 2.5L,
3.0L, 3.3L or 3.8L engines may use a back-pressure
type Exhaust Gas Recirculation (EGR) system (Fig.
12, 13, or 14). 2.5L MPI (Flexible Fuel AA-body) and
Turbo III engines do not use an EGR system. The EGR system reduces oxides of nitrogen (NOx)
in engine exhaust and helps prevent spark knock.
The system allows a predetermined amount of hot
exhaust gas to recirculate and dilute the incoming
air/fuel mixture. The diluted air/fuel mixture reduces
peak flame temperature during combustion. The EGR system consists of:
² EGR tube (connects a passage in the intake mani-
fold to the exhaust manifold)
² EGR valve
² Electronic EGR Transducer (EET)
² Connecting hoses
The electronic EGR transducer (EET) contains an
electrically operated solenoid and a back-pressure
transducer (Fig. 15). The powertrain control module
(PCM) operates the solenoid. The PCM determines
when to energize the solenoid. Exhaust system back-
pressure controls the transducer. When the PCM the solenoid, vacuum does not
reach the transducer. Vacuum flows to the trans-
ducer when the PCM de-energizes the solenoid. When exhaust system back-pressure becomes high
enough, it fully closes a bleed valve in the trans-
ducer. When the PCM de-energizes the solenoid and
back-pressure closes the transducer bleed valve, vac-
uum 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.
Fig. 11 Heated Oxygen Sensor Socket
Fig. 12 EGR SystemÐ2.2L and 2.5L TBI Engines
Fig. 13 EGR SystemÐ3.0L Engines
25 - 20 EMISSION CONTROL SYSTEMS Ä

These systems do not allow EGR at idle. The 2.2L/
2.5L EGR systems operate at all temperatures. The
3.0L, 3.3L and 3.8L EGR systems do not operate
when coolant temperature is below 4.5ÉC (40É)F at
start-up. These systems activate when coolant tem-
perature reaches 77ÉC (170ÉF).
EGR SYSTEM ON-BOARD DIAGNOSTICS
The powertrain control module (PCM) performs an
on-board diagnostic check of the EGR system on all
California vehicles with EGR systems. The diagnos-
tic system uses the Electric EGR Transducer (EET)
for the system tests. The diagnostic check activates only during selected
engine/driving conditions. When the conditions are
met, the PCM energizes the transducer solenoid to
disable the EGR. The PCM checks for a change in the oxygen sensor signal. If the air-fuel mixture goes
lean, the PCM will attempt to enrichen the mixture.
The PCM registers a fault if the EGR system has
failed or degraded. After registering a fault, the PCM
turns on the malfunction indicator lamp (instrument
panel Check Engine light). The malfunction indicator
lamp indicates the need for immediate service.
If a problem is indicated by the malfunction indicator
lamp and a diagnostic trouble code for the EGR system,
check for proper operation of the EGR system. Use the
System Test, EGR Gas Flow Test and EGR Diagnosis
Chart. If the EGR system tests properly, check the sys-
tem using the DRBII scan tool. Refer to On-Board Di-
agnosis in the General Diagnosis sections of Group 14.
Also, refer to the DRBII scan tool and the appropriate
Powertrain Diagnostics Procedure manual.
EXHAUST GAS RECIRCULATION (EGR) SYSTEM
TEST
WARNING: APPLY PARKING BRAKE AND/OR
BLOCK WHEELS BEFORE PERFORMING EGR SYS-
TEM TEST.
A failed or malfunctioning EGR system can cause
engine spark knock, sags or hesitation, rough idle,
and/or engine stalling. To ensure proper operation of
the EGR system, all passages and moving parts must
be free of deposits that could cause plugging or stick-
ing. Ensure system hoses do not leak. Replace leak-
ing components. Inspect hose connections between the throttle body,
intake manifold, EGR solenoid and transducer, and
EGR valve. Replace hardened, cracked, or melted
hoses. Repair or replace faulty connectors.
Check the EGR control system and EGR valve with
the engine fully warmed up and running (engine cool-
ant temperature over 150ÉF). With the transmission in
neutral and the throttle closed, allow the engine to idle
for 70 seconds. Abruptly accelerate the engine to ap-
proximately 2000 rpm, but not over 3000 rpm. The EGR
valve stem should move when accelerating the engine
(the relative position of the groove on the EGR valve
stem should change). Repeat the test several times to
confirm movement. If the EGR valve stem moves, the
control system is operating normally. If the control sys-
tem is not operating normally, refer to the EGR Diag-
nosis Chart to determine the cause.
EGR GAS FLOW TEST
The following procedure should be used to determine
if exhaust gas is flowing through the EGR system.
Connect a hand vacuum pump to the EGR valve
vacuum motor. With engine running at idle speed,
slowly apply vacuum. Engine speed should begin to
drop when applied vacuum reaches 2.0 to 3.5 inches.
Fig. 14 EGR MountingÐ3.3L and 3.8L Engines
Fig. 15 Electric EGR Transducer (EET) Assembly
Ä EMISSION CONTROL SYSTEMS 25 - 21

Engine speed may drop quickly or engine may even
stall. This indicates that EGR gas is flowing through
the system.If both the EGR Gas Flow Check, System Check
and Diagnosis Chart are completed satisfactorily,
then the EGR system functions normally. If engine speed does not drop off when performing
the test, remove both the EGR valve and EGR tube
and check for plugged passages. Also, check the in-
take manifold inlet passage. Clean or replace these
components for restoration of proper flow.
EGR VALVE SERVICEÐ2.2L AND 2.5L TBI
ENGINES
REMOVAL
(1) Disconnect electrical connector and vacuum
line from the electric EGR transducer (Fig. 12). (2) Remove EGR valve bolts from intake manifold.
(3) Remove EGR valve from intake manifold.
(4) Clean gasket surface and discard old gasket.
Check for any signs of leakage or cracked surfaces.
INSTALLATION
(1) Assemble EGR valve with new gasket onto the
intake manifold. (2) Install EGR valve mounting bolts. Tighten to
22 N Im (200 in. lbs.) torque.
(3) Reconnect vacuum line and electrical connector
to Electric EGR Transducer.
EGR TUBE SERVICEÐ2.2L AND 2.5L TBI ENGINES
REMOVAL
(1) Remove EGR tube attaching bolts from intake
and exhaust manifolds. (2) Remove EGR tube.
(3) Clean intake and exhaust manifold gasket sur-
faces and EGR tube flange gasket surfaces. Discard
old gaskets. (4) Check for signs of leakage or cracked surfaces
on either manifolds or tube. Replace as necessary.
INSTALLATION
(1) Loosely position EGR tube and new gaskets in
place on intake and exhaust manifolds. Install
mounting bolts. (2) Tighten attaching bolts to 22 N Im (200 in. lbs.)
torque.
EGR VALVE SERVICEÐ3.0L ENGINES
REMOVAL
(1) Disconnect the electric and vacuum connectors
from the electric EGR transducer (EET) (Fig. 16). (2) Remove EGR valve mounting bolts.
(3) Clean all gasket surfaces and discard old gas-
kets. Check for any signs of leakage or cracked sur-
faces. Repair or replace as necessary.
INSTALLATION
(1) Install EGR valve and new gasket on intake
manifold. Tighten mounting bolts to 22 N Im (200 in.
lbs.) torque. (2) Connect the electrical and vacuum connectors
to the electric EGR transducer.
EGR TUBE SERVICEÐ3.0L ENGINES
REMOVAL
(1) Remove EGR tube flange nuts from exhaust
manifold (Fig. 16). (2) Remove EGR valve nuts at intake manifold
(Fig. 16). Remove EGR tube. (3) Clean all gasket surfaces and discard old gas-
kets. Check for any signs of leakage or cracked sur-
faces. Repair or replace as necessary.
INSTALLATION
(1) Loosely install the EGR tube on the intake and
exhaust manifolds with new gaskets. (2) Tighten EGR tube flange bolts at the intake
manifold to 22 N Im (200 in. lbs.) torque.
(3) Tighten EGR tube to exhaust manifold nuts to
22 N Im (200 in. lbs.) torque.
EGR VALVE SERVICEÐ3.3L AND 3.8L ENGINES
REMOVAL
(1) Disconnect vacuum tube from electric EGR
transducer (EET). Inspect vacuum tube for damage
(Fig. 17). (2) Remove electrical connector from EET.
(3) Remove EGR valve bolts from intake manifold.
(4) Open EGR transducer clip and remove electric
EGR transducer. (5) Remove EGR valve from intake manifold.
(6) Clean gasket surface and discard old gasket.
Check for any signs of leakage or cracked surfaces.
Repair or replace as necessary.
INSTALLATION
(1) Assemble EGR valve with new gasket onto the
intake manifold. (2) Install mounting bolts. Tighten bolts to 22 N Im
(200 in. lbs.) torque. (3) Install electric EGR transducer in clip with ori-
entation tab in slot and snap closed. (4) Reconnect vacuum hose and electrical connec-
tor to EET.
EGR TUBE SERVICEÐ3.3L AND 3.8L ENGINES
REMOVAL
(1) Remove EGR tube attaching bolts from intake
and exhaust manifolds. (2) Clean intake and exhaust manifold gasket sur-
faces. Discard old gasket.
25 - 22 EMISSION CONTROL SYSTEMS Ä

(3) Check for signs of leakage or cracked surfaces
on either manifolds or tube. Repair or replace as nec-
essary.
INSTALLATION
(1) Loosely assemble EGR tube and new gaskets
into place on intake and exhaust manifolds. (2) Tighten mounting bolts to 22 N Im (200 in. lbs.)
torque.
AIR ASPIRATION SYSTEM
Certain vehicles equipped with the 2.2L or 2.5L
TBI engines have an aspirator valve (Fig. 18). The
valve uses exhaust pressure pulsation to draw fresh
air from the air cleaner into the exhaust system.
This reduces carbon monoxide (CO) and hydrocarbon
(HC) emissions. The aspirator valve works most effi-
ciently at idle and slightly off-idle, where the nega-
tive pulses are strongest. The aspirator valve
remains closed at higher engine speeds.
DIAGNOSIS
The aspirator valve is not repairable. Replace the
valve if it operates incorrectly. Valve failure results
in excessive underhood exhaust system noise at idle
and hardening of the rubber hose from the valve to
the air cleaner. Check for leakage at the aspirator
tube/catalyst assembly joint. Also, inspect the hose
connections at the aspirator valve and air cleaner for
leakage. If the aspirator tube/ catalyst assembly joint
is leaking, tighten the aspirator tube nut to 54 N Im
(40 ft. lbs) torque. If either hose connection leaks,
and the hose has not hardened, install hose clamps. To determine if the aspirator valve has failed, dis-
connect the hose from the aspirator inlet. With the
engine at idle in neutral, the negative (vacuum) ex-
haust pulses can be felt at the aspirator inlet. If hot
exhaust gas is escaping from the aspirator inlet, the
valve has failed. Replace the valve.
REMOVAL
(1) Disconnect the air hose from the aspirator
valve inlet. (2) Remove aspirator tube assembly from catalyst.
INSTALLATION
(1) Install aspirator tube. Tighten the nut to 54
N Im (40 ft. lbs) torque.
(2) Install aspirator tube bracket screw. Tighten
screw to 11 N Im (95 in. lbs) torque.
(3) Connect air hose to aspirator valve inlet and
air cleaner nipple.
Fig. 16 EGR System ServiceÐ3.0L Engines
Fig. 17 EGR SystemÐ3.3L and 3.8L Engines
Fig. 18 Air Aspirator System
25 - 24 EMISSION CONTROL SYSTEMS Ä

GROUP TAB LOCATOR
ENGINE, CHASSIS BODY
ELECTRICAL, FUEL EMISSION SYSTEMS
WIRING DIAGRAMS
SUPPLEMENTS
Service Manual Comment Forms (Rear of Manual)

To protect the consumer from theft and possible
fraud the manufacturer is required to include a
Check Digit at the ninth position of the Vehicle Iden-
tification Number. The check digit is used by the
manufacturer and government agencies to verify the
authenticity of the vehicle and official documenta-
tion. The formula to use the check digit is not re-
leased to the general public.
BODY CODE PLATE LOCATION AND DECODING
INFORMATION
The Body Code Plate is attached to the top of the
radiator closure panel in the engine compartment.
There are seven lines of information on the body code
plate. Lines 4, 5, 6, and 7 are not used to define ser-
vice information. Information reads from left to
right, starting with line 3 in the center of the plate
to line 1 at the bottom of the plate.
BODY CODE PLATE LINE 3
DIGIT BOXES 1,2 AND 3Ð Paint Procedure
DIGIT BOXES 4 THROUGH 7Ð Primary Paint
See Group 23, Body for color codes
DIGIT BOXES 8 THROUGH 11Ð Secondary Paint
DIGIT BOXES 12 THROUGH 15Ð Interior Trim Code
DIGIT BOXES 16, 17 AND 18Ð Engine Code
² EDB = 2,5 L, 4 cylinder EFI GasÐWith Balance
Shaft
² EDF = 2.2 L, 4 cylinder EFI GasÐAutomatic or
Manual Transaxle
² EDM = 2.5 L, 4 cylinder EFI GasÐAutomatic or
Manual Transaxle
² EDN = 2.5 L, 4 cylinder EFI Flexible FuelÐAu-
tomatic Transaxle
² EDS = 2.2 L, 4 cylinder, 16 valve Turbo IIIÐMan-
ual Transaxle
² EFA = 3.0 L, V6 Gas (EFI)ÐAutomatic or Man-
ual Transaxle
² EGA = 3.3 L, V6 Gas (EFI)ÐAutomatic
² EGH = 3.8 L, V6 Gas (EFI)ÐAutomatic
BODY CODE PLATE LINE 2
DIGIT BOXES 19 THROUGH 30Ð Vehicle Order Number
DIGIT BOXES 31, 32 AND 33Ð Vinyl Roof Code
DIGIT BOXES 34, 35 AND 36Ð Vehicle Shell Car Line
² APD = Shadow
² APP = Sundance
² AAC = Lebaron Sedan
² AAD = Spirit
² AAP = Acclaim
² AGV = Daytona, IROC R/T
² AJC = LeBaron Coupe/Convertible
VIN CODE BREAKDOWN
2 INTRODUCTION Ä

TORQUE REFERENCES
Individual Torque Charts appear at the end of many
Groups. Refer to the Standard Torque Specifications
and Bolt Identification Chart in this Group for torques
not listed in the individual torque charts (Fig. 4).
Torque specifications on the Bolt Torque chart are
based on the use of clean and dry threads. Reduce the
torque by 10% when the threads are lubricated with
engine oil and by 20% if new plated bolts are used. Various sizes of Torx head fasteners are used to
secure numerous components to assemblies. Due
to ever changing usage of fasteners, Torx head
fasteners may not be identified in art or text .
METRIC THREAD AND GRADE IDENTIFICATION
Metric and SAE thread notations differ slightly. The
difference is illustrated in Figure 5. Common metric fastener strength classes are 9.8
and 12.9 with the class identification embossed on
the head of each bolt (Fig. 6). Some metric nuts will
be marked with a single digit strength number on
the nut face.
SAE strength classes range from grade 2 to 8 with
line identification embossed on each bolt head. Mark-
ings corresponding to two lines less than the actual
grade (Fig. 7). For Example: Grade 7 bolt will exhibit
5 embossed lines on the bolt head.
METRIC SYSTEM
Figure art, specifications, and tightening references
in this Service Manual are identified in the metric
system and in the SAE system. During any maintenance or repair procedures, it is
important to salvage metric fasteners (nuts, bolts,
etc.) for reassembly. If the fastener is not salvage-
able, a fastener of equivalent specification should be
used.
Fig. 6 Metric Bolt Identification
Fig. 7 SAE Bolt Identification
Fig. 4 Grade 5 and 8 Standard Torque Specifica- tions
Fig. 5 Thread Notation (Metric and SAE)
6 INTRODUCTION Ä