EGR system malfunctions can cause engine stalling at idle, rough engine idling, detonation (knock), and poor fuel economy. If the EGR valve sticks open, it will act as a large vacuum leak, causing a lean air-fuel mixture. The engine will run rough at idle or stall. If the EGR fails to open or the exhaust passage is clogged, higher combustion temperatures can cause abnormal combustion (detonation) and knocking.
EGR system maintenance
Maintenance intervals for the EGR system vary with vehicle manufacturer. Refer to a service manual for exact distance or time intervals.
Also, check that the vacuum hoses in the EGR system are in good condition. They can become hardened, which can cause leakage.
EGR system testing
To test an EGR system start, idle, and warm the engine. Operating the carburettor or throttle body accelerator linkage by hand, increase engine speed to 2000-3000 rpm very quickly. If visible, observe the movement of the EGR valve stem. The stem should move as the engine is accelerated. If it does not move, the EGR system is not functioning. Sometimes the EGR valve stem is not visible. You then need to test each EGR system component separately. Follow the procedures described in a service manual.
To test the EGR VALVE, idle the engine. Connect a hand vacuum pump to the EGR valve, Fig. 32-8.
Plug the supply vacuum line to the EGR valve. When vacuum is applied to the EGR valve with the pump, the engine should begin to MISS or STALL. This lets you know that the EGR valve is opening and that exhaust gases are entering the intake manifold.
If the EGR valve does NOT affect engine idling, remove the valve. The valve or the exhaust manifold passage could be clogged with carbon. If needed, clean the EGR valve and exhaust passage. When the EGR valve does not open and close properly, replace valve.
EGR valves which provide electrical data to a computer control system require special testing procedures. Refer to a workshop manual covering the specific system. Component damage could result from an incorrect testing method.