light CHEVROLET DYNASTY 1993 Service Manual

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

(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

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