Diesel Trucks (5.9L)
EGR system operation must first be checked with the DRB scan tool. To perform a test of the EGR system, refer to the appropriate Powertrain Diagnostic Procedures service manual. Check and correct any electrical malfunctions before proceeding.
Do not attempt to diagnose a defective EGR valve by applying vacuum to the EGR valve diaphragm fitting with engine running. Opening the EGR valve at idle speed will not change idle speed.
- Check operation of EGR valve vacuum regulator solenoid and EGR system with DRB scan tool.
- Start engine and verify that vacuum is available at inlet fitting of EGR valve vacuum regulator solenoid. Vacuum is supplied by an engine driven vacuum pump Engine Vacuum Pump. Refer to BRAKES for vacuum pump specifications and test procedures.
- Check EGR valve for operation and leaks. Use the following test procedure to determine if exhaust gas is flowing through the EGR valve. It can also be used to determine if the EGR tube is plugged, or the system passages in the intake or exhaust manifolds are plugged.
- Use the following test procedure to determine if exhaust gas is flowing through the EGR valve. It can also be used to determine if the EGR tube is plugged, or the system passages in the intake or exhaust manifolds are plugged. To verify EGR valve operation, it must be removed from intake manifold. Refer to EGR Valve Removal/Installation procedures. Examine the head of poppet valve at base opening on bottom of EGR valve. Look for heavy carbon build-up. A coating of carbon is normal with engine operation. Shine a bright light through valve opening and examine edge (seat) of poppet valve. No light should be evident at valve edge. If either condition exists, replace EGR valve. Do not attempt to clean the poppet valve within the EGR valve assembly. The EGR valve is equipped with a fitting located on the EGR valve vacuum motor. Connect a hand - held vacuum pump equipped with a vacuum gauge to this fitting. Slowly apply 10 inches HG of vacuum to the fitting on the EGR valve motor. The poppet valve should start to open at approximately 10 inches of vacuum. Vacuum should hold steady at 10 inches. If not, replace the EGR valve. If vacuum holds steady at 10 inches, and poppet valve has started to open, proceed to next step. Continue to apply vacuum until gauge reading is at 20 inches. The poppet valve should be fully open at approximately 20 inches of vacuum. Vacuum should also hold steady at 20 inches. If not, replace the EGR valve. If the EGR valve tested OK, the EGR tube may be plugged with carbon, or the passages in the intake and exhaust manifolds may be plugged with carbon. While the EGR valve is removed, check passages in EGR tube. Remove the EGR tube between the intake and exhaust manifolds. Check and clean the EGR tube and its related openings on the manifolds. Refer to EGR Tube Removal/Installation. While the EGR valve is removed, check for carbon build-up at intake manifold openings. Clean carbon deposits as necessary.
- Check operation of one-way check valve EGR Valve and Components. A quick-release type, one-way check valve is located in the vacuum line between the EGR valve and the EGR valve vacuum regulator solenoid. This check valve allows engine vacuum to be quickly bled from EGR valve. If the valve is defective, vacuum will be stored in the EGR valve diaphragm motor (EGR valve will remain open) If the valve is leaking, the EGR valve may not open. Attach a vacuum gauge with a "T" fitting into the vacuum line at EGR valve (between EGR valve and EGR vacuum regulator solenoid). Bring engine to operating temperature to allow EGR system operation. While driving at steady speed, high vacuum should be observed at gauge. Quickly open the throttle while observing gauge. Gauge should immediately drop to 0 inches. If any vacuum is being stored (gauge reading anything other than 0 inches), test EGR system electrical operation using the DRB scan tool. If EGR system electrical operation is OK, but gauge reading has not dropped to 0 inches, proceed to next step before replacing check valve. Disconnect the vacuum lines at both ends of check valve and remove valve from vehicle. Attach a hand-operated vacuum pump equipped with a vacuum gauge to the inlet fitting on check valve (to solenoid). The inlet end of fitting is marked with an S. Apply a minimum of 20 in. vacuum or more to this fitting while plugging opposite fitting with a finger. Vacuum gauge should remain constant at 20 or more inches without any leakage. If not, replace check valve. Attach vacuum pump to the fitting at EGR valve end of check valve. Apply vacuum to this fitting while plugging opposite fitting with a finger. While operating vacuum pump, vacuum gauge should remain at or near 0 inches. If any vacuum is being stored, replace check valve.