4.2L & 5.9L Only
- With engine at normal operating temperature and at curb idle speed, rapidly open and close throttle. Open throttle sufficiently to obtain at least 1500 RPM. A distinct movement should be noticed in EGR diaphragm.
- If diaphragm does not move, probable causes are: faulty vacuum signal to EGR, defective EGR diaphragm or defective backpressure sensor diaphgram (if equipped). Repair, correct or replace as necessary.