DRIVEABILITY EXHAUST ODOR INSPECTION/MAINTENANCE/PROM

Model and Year: 1987-88 C/G/K/M/R/V TRUCKS EQUIPPED WITH 4.3L (VIN CODE Z) ENGINE

This bulletin cancels and supersedes Chevrolet Dealer Service bulletin #87-256-6E, dated January, 1988. All copies should be destroyed.

This bulletin expands the application to include 1987 and 1988 C, G, K, R, V trucks, all 1987 M vans, and 1988 M vans prior to VIN 191855.

Some 1987 and 1988 vehicles equipped with 4.3L engines (VIN Code Z), including 1988 M vans with VIN's prior to those listed above, may exhibit one or more of the conditions listed below.

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. CALIBRATION PROMS ARE PARTICULAR TO OXYGEN SENSOR LOCATION AND SHOULD NOT BE INTERCHANGED. CALIBRATION PROMS LISTED IN THIS BULLETIN ARE APPROPRIATE FOR VEHICLES WITH THE OXYGEN SENSOR LOCATED IN THE EXHAUST MANIFOLD ONLY. ALSO, A BLEED CONNECTOR SHOULD NOT BE INSTALLED IN A VEHICLE EQUIPPED WITH AN OXYGEN SENSOR LOCATED IN THE Y-PIPE AS AN OVER RICH CONDITION WITH INCREASED SULFUR ODOR AND DEGRADED DRIVEABILITY MAY RESULT.

Driveability Conditions

- Driveability sag or hesitation during the first five minutes of operation after a cold start or within one minute of operation after a hot restart.

- Surge at speeds of 40-50 mph during a cruise or light throttle application.

- Long crank time or false start after a 1-3 hour hot soak

Inspection/Maintenance Testing ------------------------------

- Difficulty in meeting state exhaust emission inspection/maintenance testing requirements.

Exhaust Odor Condition

- Hydrogen sulfide smell typically described as "rotten egg smell" at idle.

Service Procedure

If a vehicle, exhibiting one or more of the conditions described, can not be repaired by using normal service procedures, the following should be performed:

Condition Service Procedure --------- -----------------

Driveability Use a "Scan" tool to check PROM i.d., determine if the vehicle has the appropriate calibration PROM as listed in the table below. If the vehicle is not equipped with the calibration PROM listed, install the PROM specified.

Inspection/Maintenance Use a "Scan" tool to check PROM Determine if the i.d., and/or Exhaust vehicle has the appropriate calibration PROM as in Odor the table below. If the vehicle is not equipped with the calibration PROM listed, install the PROM specified.

In addition, install bleed orifice connector, P/N 10105820 per the instructions on page 4 of this bulletin.

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) ------------------------------------------------------------------------

C,K A3 (M40) All 16082083 AKDW 2251 A4 (MD8) All 16082087 AKDX 2261 M5 (MG5) All 16082093 AKDY 2271 M4C(M20) except C10 All 16079234 AJST 8951 ------------- C10(only) M4C(M20) All 16076291 ADUH 3471

R,V A3 (M40) All 16082083 AKDW 2251 A4 (MD8) All 16082087 AKDX 2261 M3(M64), M40D(MY6) All 16079234 AJST 8951 and M4C(M20)

G A3 (M40) All 16082083 AKDW 2251 A4 (MD8) All 16082087 AKDX 2261 M3(M64), M40D(MY6) All 16082103 AKFA 2291

M A4 (MD8) All 16082087 AKDX 2261 M5 (MH3) 2.73 16088400 AMJL 8401 M5 (MH3) 3.08/3.42 16082103 AKFA 2291

California Emissions Packages

Truck Transmission Service PROM PROM I.D. Model Model (RPO) Axle PROM KIT P/N LABEL (Scanner) ------------------------------------------------------------------------

C A4 (MD8) All 16088362 AMDA 8351 M4C (M20) All 16087034 AMBU 7281 M5 (MG5) All 16087029 AMBT 7271

K A4 (MD8) All 16076224 ADUT 3561 M4C (M20) All 16079238 AJSU 8961 M5 (MG5) All 16076201 ADUN 3521

R A4 (MD8) All 16088362 AMDA 8351 M40D(MY6),M4C(M20) All 16087034 AMBU 7281

V A4 (MD8) All 16076224 ADUT 3561 M4C (M20) All 16079238 AJSU 8961

G A4 (MD8) All 16088362 AMDA 8351 M3(M64),M40D(MY6) All 16087020 AMBR 7251

M A4 (MD8) All 16088362 AMDA 8351 M5 (MH3) 2.73 16087025 AMBS 7261 M5 (MH3) .08/3.42 16087020 AMBR 7251

Bleed Orifice Installation Procedure

1. Disconnect the EGR vacuum line currently on port "J" on the front of the TBI unit. See Figure 1.

2. Install connector bleed assembly, P/N 10105820 on port "J" of the TBI unit.

3. Reconnect the EGR vacuum line remove from port "J" to the open end of the connector bleed assembly.

Labor Operation Labor Number Time Description ------ --------- ----------- T7455 .3 Hours Identify existing PROM and install connector bleed assembly.

Add .2 Hours To change PROM if necessay.

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.