Exhaust Gas Recirculation: Testing and Inspection

***THIS ARTICLE INCLUDES UPDATES MADE BY TECHNICAL SERVICE BULLETIN 61-65-21, DATED APRIL, 1996***

Movement Of EGR Valve Diaphragm:

Comp. Loc:

EGR SYSTEM DIAGNOSIS
If Exhaust Gas Recirculation (EGR) valve fails to operate properly, any of the following areas could be the cause:

^ Vacuum hoses.
^ EGR valve.
^ EGR pressure transducer.
^ EGR Solenoid Vacuum (EGR SV) valve.

NOTICE: Before inspecting the EGR system be sure to confirm the following:

^ Engine Coolant Temperature (ECT) sensor, Throttle Position (TP) sensor, Vehicle Speed Sensor (VSS) and Mass Air Flow (MAF) sensor are not malfunctioning. If one of the above inputs is not present, the EGR system will not operate.

INSPECT
1. Raise and suitably support vehicle drive axles. Place the transmission in neutral and the transfercase in "2H." Check that the propeller shaft is turning (ECM must see VSS input for operation of EGR solenoid vacuum valve).

CAUTION: Make sure that the transmission is set to the "Neutral" position for this check. If it is set to any other position, the drive wheels may turn at high speeds and a hazardous situation could occur.

2. When engine is cold (ECT is below 55°C [131°F]) start engine. With finger on diaphragm, momentarily raise engine speed above 3,500 RPM. Check EGR valve diaphragm and ensure that there is no movement.

WARNING: If EGR valve is hot, it may be necessary to wear gloves to avoid burning fingers.

3. Warm up the engine to normal operating temperature and momentarily raise engine speed above 3,500 RPM. Check the diaphragm to ensure that it moves forward during acceleration and backward during deceleration.
4. Keep engine running at idle speed and open the EGR valve by hand. The engine should slow down and run rough or stall. If neither occurs, EGR passage is clogged and must be cleaned.