DRIVEABILITY EXHAUST ODOR INSPECTION/MAINTENANCE/PROM

VEHICLES AFFECTED: 1987 AND 1988 C/G/K/M/R/V TRUCKS EQUIPPED WITH 4.3L ENGINE (ENGINE VIN CODE Z)

This bulletin canels and supercedes GM of Canada bulletin #87-643-110 date December, 1987.

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 Chevrolet VIN 191855 and GMC VIN 523374.

Some 1987 and 1988 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 60-80 kph (40-50 mph) during a cruise or light throttle application.

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

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.

Exhaust Odor 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.

In addition, install bleed orifice connector, P/N 10105820 per the instructions at the end 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 CIO 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

Connect Bleed Assembly 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.

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.