EXHAUST ODOR AT IDLE RELOCATE 02 SENSOR/ Y PIPE

VEHICLES AFFECTED: 1988 M VAN (ONLY) W/4.3L, ENGINE (VIN) Z

Some 1988 M vans equipped with 4.3L (VIN Code Z) engines built prior to Chevrolet VIN 191855 and GMC VIN 523374 may exhibit an exhaust odor often described as sulfur or rotten egg smell at idle following sustained highway driving or trailer towing.

This condition can be addressed by relocating the oxygen sensor from the left hand exhaust manifold to the exhaust takedown or Y-pipe and installing the appropriate calibration PROM.

NOTICE: 1988 M VANS BUILT AFTER THESE VIN's ARE EQUIPPED WITH AN OXYGEN SENSOR LOCATED IN THE EXHAUST Y-PIPE AND AN APPROPRIATE CALPROM.

Parts Required

To accomplish this, it will be necessary to obtain the required parts listed below:

- exhaust Y-pipe P/N 15598249

- plug P/N 10017198

- the appropriate PROM from the table below

Calibration PROM Table

Federal/Altitude Emissions Packages (NA5 and NA6) -------------------------------------------------

Truck Transmission Service PROM PROM I.D. Model Model (RPO) Axle PROM Kit P/N Label (Scanner) ----- ----------- ----- ------------ ----- ---------- M A4 (MD8) All 16121142 AKMH 3051 M5 (MH3) All 16120722 AKSP 3561

Service Procedure

1. Disconnect the battery.

2. Check to determine if a bleed has been installed at port "J" on the TBI unit during previous repairs. If so, remove the bleed connector assembly and reconnect the vacuum hose to port "J". (It is necessary to remove the bleed when relocating the oxygen sensor to the Y-pipe because the air bleed will result in artifically lean readings by the oxygen sensor at the new location. Failure to remove the bleed will result in the system adding additional fuel and possibly worsen the odor condition.)

3. Remove the exhaust Y-pipe and discard.

4. Install new Y-pipe, P/N 15598249

5. Remove the oxygen sensor from the left exhaust manifold and install it in the boss provided in the newly installed Y-pipe using a small amount of anti-seize compound as described in the service manual. Torque to (30 ft.lbs). It will be necessary to remove the wiring harness cover and untape the existing 02 sensor lead a short distance up the harness. No splicing is necessary. The lead should be routed as shown in the Illustration below. Care should be exercised so that the lead does not contact the sharp edge of the dipstick tube bracket.

6. Install plug, P/N 10017198, i n the former oxygen sensor location in the left exhaust manifold.

7. Install the appropriate PROM from the table provided.

8. Reconnect the battery.

9. Run the engine and check the exhaust manifold to Y-pipe connections for leaks. Repair any leaks found. If a leak exists between the engine and the 02 sensor location, it may cause the exhaust odor condition to continue.

Labor Operation Number: T7620

Labor Time : .9 Hours

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.