What is the proper testing procedure for conducting an EGR functional test?

What is the proper testing procedure for conducting an EGR functional test?

• A. With the engine running at 2000 RPM, apply vacuum to the valve and listen for an RPM drop.
• B. With the engine running at idle, apply vacuum to the valve and listen for an RPM rise.
• C. With the engine at 3000 RPM, apply vacuum and listen for RPM rise.
• D. With the engine at 1000 RPM, remove the EGR valve.

Answer: (A)

The test checks whether the EGR valve opens and affects engine operation when vacuum is applied. When you hold the engine at about 2000 RPM and apply vacuum to the EGR valve, a properly functioning valve will open and cause the engine speed to drop. That drop shows the exhaust gas recirculation is occurring and pulling enough inert gas into the intake to slow the engine slightly. If there’s little or no change, the valve isn’t opening correctly or the vacuum source isn’t delivering vacuum. Testing at idle wouldn’t reliably show the valve’s response, and applying vacuum at a much higher rpm won’t reflect normal operating conditions. Removing the EGR valve isn’t a functional test. So applying vacuum at around 2000 RPM with observation of a real RPM drop is the correct procedure.

The test checks whether the EGR valve opens and affects engine operation when vacuum is applied. When you hold the engine at about 2000 RPM and apply vacuum to the EGR valve, a properly functioning valve will open and cause the engine speed to drop. That drop shows the exhaust gas recirculation is occurring and pulling enough inert gas into the intake to slow the engine slightly. If there’s little or no change, the valve isn’t opening correctly or the vacuum source isn’t delivering vacuum.

Testing at idle wouldn’t reliably show the valve’s response, and applying vacuum at a much higher rpm won’t reflect normal operating conditions. Removing the EGR valve isn’t a functional test. So applying vacuum at around 2000 RPM with observation of a real RPM drop is the correct procedure.