SER. MANUAL UPDATE SEC.6E-7C EGR SYSTEM SERVICE PROCEDURE

SUBJECT: SERVICE INFORMATION MANUAL UPDATE - SECTION OB - MAINTENANCE AND LUBRICATION, SECTION 6E-C7 EGR SYSTEM PROCEDURE

I. Please update your 1990 DeVille and Fleetwood Service Information Manual, Section OB, to include the following note on EGR system service.

EGR System Service - Section 0B:

Conduct EGR system service as covered in Section 6E-C7.

IMPORTANT: Inspect the EGR valve and mounting chamber gasket for leaks at each 30,000 miles (50,000 km). A leak can be heard with the engine idling and the hood open (sounds like an exhaust leak). If a leak is found, replace the gasket(s) and torque the bolts to specifications.

II. Please update your 1990 DeVille and Fleetwood Service Information Manual, Section 6E-C7, to include the following procedure for EGR system service.

EGR System Service - Section 6E-C7:

Whenever the EGR valve is removed, or during regularly scheduled EGR system maintenance, the EGR system should be inspected and cleaned. This will ensure that the EGR system will function properly under all operating conditions. Proper EGR system service consists of the following four steps:

A. EGR System Diagnosis

Diagnosis of the EGR system should be performed if required by engine performance or engine driveability symptoms. Refer to "EGR Diagnosis" in this section.

B. EGR Valve Cleaning

1. Remove the EGR valve from the engine.

2. Hold the valve in you hand. Tap on the end of the round pintle using a light snapping action with a plastic hammer. This will remove the exhaust deposits from the valve seat. Remove all loose particles.

3. Clean the mounting surface of the valve with a wire wheel or wire brush, and the pintle with a wire brush.

4. Depress the valve diaphragm and check the seating area for cleanliness and signs of rubbing by looking through the valve outlet. If pintle or seat are not completely clean, repeat step 2.

5. Hold bottom of valve securely and try to rotate top of valve back and forth. Replace valve if any looseness is felt.

6. In ect the valve outlet for deposits. Remove any deposit build up with a screwdriver or other sharp tool. Do not wash the EGR valve in solvents or degreaser; permanent damage to the valve diaphragm may result. Sand blasting of the valve is not recommended as this may affect proper valve operation.

7. Clean the EGR passages in the intake manifold. Use care to ensure that all loose articles are completely removed to prevent them from clogging the EGR valve or being ingested into the engine.

8. Clean the manifold mounting surface. Do not reinstall the EGR valve at this time.

C. EGR Stack Tube Cleaning

9. Remove the throttle body. Refer to Section 6E-C2 for more information.

10. Inspect the EGR stack tubes in the floor of the intake manifold for carbon deposits. If necessary, clean the carbon from the EGR stack tubes using an 11/32" drill bit. Use caution to avoid drilling into or damaging the bottom of the intake manifold. CAUTION: For the next step safety glasses must be worn.

11. Cover the top end of one EGR stack tube with a piece of tape. Hold a shop rag over the EGR valve opening on the manifold. Using compressed air, blow through the uncovered EGR stack tube to force the carbon debris out through the EGR valve opening in the manifold and into the shop rag. Remove the tape from the covered tube.

12. Install the EGR valve using a new gasket.

D. Throttle Body Cleaning

13. Clean the throttle valves and throttle body passages of all carbon deposits. Refer to "Throttle Body Cleaning" in Section 6E-C1.

14. Reinstall the throttle body using a new gasket.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.