DR-26C Checking EGR Back Pressure

1. With engine operating, disconnect EGR vacuum supply hose from back pressure valve and connect a vacuum gauge to hose.
2. Operate engine at 2000 RPM and note vacuum gauge reading.
3. If vacuum gauge reading is above 5 inches of vacuum, replace EGR back pressure valve.
4. If vacuum gauge reading is 0, check vacuum supply from throttle body.