Chart C-7, EGR Check
The EGR valve is opened by vacuum to let exhaust gasses into the combustion chamber through the intake manifold. These inert gasses help to lower peak combustion chamber temperatures, which will eliminate detonation (pinging) and reduce the formation of oxides of nitrogen (NOx). If the volume of these gasses is too great or gasses are allowed to flow at the improper time, combustion air/fuel mixture may become "diluted" and a misfire occur. The amount of EGR valve flow is controlled by variations in vacuum and the EGR vacuum control solenoid.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- Checks for sticking EGR valve. If sticking, remove and examine valve to determine whether it can be cleaned, or must be replaced. A sticking EGR valve will cause a rough idle condition.
- Checks for plugged EGR passages. If passages are plugged, the engine may have severe detonation on acceleration.