Symptom Related Diagnostic Procedures

WARNING: BE SURE TO APPLY PARKING BRAKE IDLE CHECK OR ADJUSTMENT, OR ANY ENGINE
AND/OR BLOCK WHEELS BEFORE PERFORMING RUNNING TESTS.

Condition Possible Cause Correction

EGR VALVE STEM DOES (a) Cracked, leaking, disconnected or (a)Verify correct hose connections and
NOT MOVE ON SYSTEM plugged hoses. leak check to confirm that all hoses
TEST. are open. If defective hoses are
found, replace hose harness.
(b)Defective EGR valve, ruptured (b)Disconnect hose harness from EGR
diaphragm or valve stem frozen. valve. Connect external vacuum
source, 10 inches Hg or greater, to
valve diaphragm. If no valve
movement occurs, replace valve. If
valve opens, approximately 1/8 inch
(3.0 mm) travel, pinch off supply hose
to check for diaphragm leakage.
Valve should remain open 30
seconds or longer. If leakage occurs,
replace valve.

EGR VALVE STEM DOES (a-1) Defective CTS (a-1) Bypass EGR solenoid and connect
NOT MOVE ON SYSTEM amplified venturi vacuum directly to
TEST, OPERATES EGR valve. If normal operation of
NORMALLY ON EXTERNAL EGR stem is observed, further
VACUUM SOURCE. diagnosis of the CTSEGR system is
required. With engine warmed up,
remove wire from center terminal of
the CTS. Wait 90 seconds. If EGR
valve operates, replace CTS.
To check CTS with engine cold,
remove both wires from the CTS. Use
an ohmmeter to check the resistance
of the switch. If the resistance is
greater than 10 ohms, replace the
switch. If the resistance is not greater
than 10 ohms, check the continuity
of the ground circuit.

EGR VALVE STEM DOES (a-2) Defective CVS5P valve. (a-2) Bypass valve so that amplifier is
NOT MOVE ON SYSTEM connected directly to EGR valve. If
TEST, OPERATES normal operation of EGR valve stem
NORMALLY ON EXTERNAL is restored, replace CVS5P valve.
VACUUM SOURCE. (CON'T) (b)Defective coolant temperature (B) To check coolant temperature sensor,
sensor. remove wiring connector from coolant
temperature sensor. Use an
ohmmeter to check resistance of
sensor. Ohmmeter should read as
follows:
382,000 to 22,000 ohms at (-40°
to 20°F) 36,000 to 3,300 ohms at
(500 to 100°F) 3,900 to 176 ohms
at 140° to 245°F.)
If resistance is okay, repair wires
between computer and sensor for
open or short. If resistance is not
okay, replace coolant temperature
sensor.
(c) Defective EGR vacuum control (c-1) Engine running. Connect voltmeter
solenoid. to gray wire of EGR vacuum solenoid
and ground. With engine temperature
below 50°F-4 BBL. voltmeter should
read 0-1 volts. Voltage above 1 volt,
perform next test.

(c-2) Engine running. Connect voltmeter
to blue wire of EGR vacuum solenoid.
Voltmeter should read within one volt
of battery voltage. Voltage OK replace
EGR vacuum solenoid. 0 volts repair
wire harness to ignition switch for an
open circuit.
(d) Defective vacuum control unit (d) Venturi Vacuum Control System:
(amplifier). Remove venturi signal hose from
nipple on carburetor. With engine
operating at idle, apply a vacuum of
one to two inches Hg to venturi signal
hose. Engine speed should drop a
minimum of 150 RPM and EGR valve
stem should visibly move 1/8 inch
(3.0 mm) or more. If this does not
occur, replace vacuum control unit.
(e) Plugged carburetor venturi signal (e) If vacuum control unit (amplifier),
passage. operates normally in previous test,
plugged vacuum tap to carburetor
venturi is indicated. Use suitable
carburetor solvent to remove deposits
from passage and use light air
pressure to verify that passage is
clear.

ENGINE WILL NOT IDLE, (a)Control system defective-EGR (a)Disconnect hose from EGR valve and
DIES OUT ON RETURN TO valve open. plug hose-recheck idle. If
IDLE OR IDLE IS VERY satisfactory, replace vacuum control
ROUGH OR SLOW. unit (amplifier).
(b)High EGR valve leakage in closed (b)If vacuum hose removal does not
position. correct, remove EGR valve and
inspect to insure poppet is seated.
Clean deposits if necessary, or
replace valve if found defective.

WEAK WIDE OPEN (a)Defective vacuum control unit (a)Disconnect hose from EGR valve and
THROTTLE (amplifier). plug the hose. Road test the vehicle,
PERFORMANCE. if performance is restored, replace
vacuum control unit.

Do not use drills or wires to clean carburetor control passages for either type of control system as calibration of precision control orifices may be altered resulting in unsatisfactory vehicle operation.