When testing an EGR system for proper operation using a vacuum gauge, how much should intake manifold vacuum drop when the EGR valve is commanded open by a scan tool?

Question

Quizplus · Accepted Answer

When the EGR valve is commanded open, the intake manifold vacuum should drop by about 6-8 inches of mercury (in. Hg). This is because the EGR system recirculates a portion of an engine's exhaust gas back to the engine cylinders, reducing the oxygen content in the intake air, which in turn reduces peak combustion temperatures and reduces NOx emissions. The drop in vacuum is a result of the introduction of this exhaust gas into the intake manifold, which disrupts the vacuum being generated by the engine's intake stroke.

When Testing an EGR System for Proper Operation Using a Vacuum