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EGR Functional Tests

EGR Control Valve:





FUNCTIONAL TEST
1. Warm up engine and allow the engine to idle in neutral or park for at least two minutes.
2. Disconnect the hose at the EGR valve and connect a vacuum gauge. Open and close the throttle quickly several times and verify a fluctuation of several inches of vacuum.
3. Remove the vacuum gauge and attach a vacuum pump to the EGR valve. Apply at least 15 inches Hg vacuum directly to the valve, the engine speed should drop several hundred RPM, stumble or stall.
4. Disconnect the vacuum pump and reconnect the EGR system hose to the EGR valve.
5. A properly operating system will pass both of these tests. If either test fails, refer to the EGR Diagnosis.




DIAGNOSIS
EGR VALVE STEM DOES NOT MOVE ON SYSTEM TEST

Possible Cause Cracked, leaking, disconnected or plugged hoses

Correction Verify correct hose connections and leak check to confirm that all hoses are open. If defective hoses are found, replace hose harness.

Possible Cause Defective EGR valve, ruptured diaphragm or valve stem frozen

Correction Disconnect hose harness from EGR valve. Connect external vacuum source, 10 inches Hg or greater, to the valve diaphragm. If no valve movement occurs, replace valve. If valve opens, approximately 1/8 inch 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 NOT MOVE ON SYSTEM TEST, OPERATES NORMALLY ON EXTERNAL VACUUM SOURCE


Possible Cause Defective charge temperature sensor

Correction To check charge temperature sensor, remove wiring connector from charge temperature sensor. Use a 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 (50° 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 charge temperature sensor.

Possible Cause Defective EGR vacuum control solenoid


Correction a. With engine running, connect a voltmeter to gray wire of EGR vacuum solenoid and ground. With engine temperature below 70°F - 2 BBL. and 50°F - 4 BBL. voltmeter should read 0-1 volts. Voltage above 1 volt, perform next test.
b. Turn the engine off. Disconnect the computer 12 way connector. Connect a voltmeter to cavity No. 7 of the 12 way connector and ground. Turn the ignition switch to the run position. Voltmeter should read within 1 volt of battery voltage. If voltage is okay, replace computer. 0 volt, repair the wire of cavity No. 7 for an open circuit to the EGR vacuum solenoid.
c. With engine running, connect voltmeter to blue wire of EGR vacuum solenoid. Voltmeter should read within 1 volt of battery voltage. Voltage okay, replace EGR vacuum solenoid. 0 volts, repair wire harness to ignition switch for an open circuit.

Possible Cause Defective vacuum control unit (amplifier)

Correction a. (5.2L 4 v) Venturi Vacuum Control System: 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.

Possible Cause Plugged carburetor vacuum signal passage

Correction a. (5.2L 2 V) Remove ported signal hose from carburetor. Connect a hand vacuum source to nipple. With engine at idle, apply at least 5 inches Hg of vacuum to nipple, engine rpm should drop a minimum of 150 rpm. If rpm does not drop, a plugged carburetor passage is indicated. Use a suitable cleaner to open passage.

b. (5.2L 4 v)If vacuum control unit (amplifier), operates normally in previous test, plugged vacuum tap to carburetor is indicated. Use suitable carburetor cleaner to open passage.

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

ENGINE WILL NOT IDLE, DIES OUT ON RETURN TO IDLE OR IDLE IS VERY ROUGH OR SLOW

Possible Cause Control system defective-EGR valve open

Correction Disconnect hose from EGR valve and plug hose-recheck idle. If satisfactory, replace vacuum control unit (amplifier).

Possible Cause High EGR leakage in closed position

Correction If vacuum hose removal does not correct, remove EGR valve and inspect to insure poppet is seated. Clean deposits if necessary, or replace valve if found defective.

WEAK WIDE OPEN THROTTLE PERFORMANCE

Possible Cause Defective vacuum control unit (amplifier)

Correction Disconnect hose from EGR valve and plug the hose. Road test vehicle, if performance is restored, replace vacuum control unit.







SOLENOID TEST
1. Ensure all vacuum hose connections are correct and not leaking.
2. Disconnect electrical connector from solenoid valve.
3. Connect either solenoid terminal to a ground and the other one to the battery positive terminal, then listen for clicking noise from solenoid as it is connected to battery positive terminal.
4. To test valve operation, let engine idle, then increase engine speed to approximately 2000 RPM. If EGR control valve stem does not move, replace delay solenoid.

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