Emission - Driveability/Exhaust Odor/Emission Testing
88chevy23GMC NUMBER: 88-T-119
GROUP: 6E - Engine Emissions
DATE: May, 1988
CORPORATE
NUMBER: 836517
SUBJECT: DRIVEABILITY, EXHAUST ODOR, INSPECTION/MAINTENANCE TESTING
MODELS: 1987 AND 1988 C/K, R/V, G, AND M TRUCKS EQUIPPED WITH 4.3L ENGINE (ENGINE VIN CODE Z)
THIS BULLETIN CANCELS AND SUPERSEDES GMC TRUCK BULLETIN #87-T-107, DATED DECEMBER, 1987, ALL COPIES OF WHICH SHOULD BE DESTROYED.
This bulletin expands the application to include 1987 and 1988 C/K, R/V, G, and M trucks, all 1987 M vans, and 1988 M vans prior to GMC VIN 523374.
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. M-VAN 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.
Some 1987 and 1988 trucks 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.
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, cannot 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/ Use a "Scan" tool to check PROM I.D., determine if the vehicle has the appropriate
Maintenance and/or calibration PROM as listed in the table below. If the vehicle is not equipped with the
Exhaust Odor calibration PROM listed, install the PROM specified.
In addition, install bleed or orifice connector, P/N 10105820 per the instructions at the end of this bulletin.
Calibration PROM Table
FIGURE 1:
Connector Bleed Assembly Installation Procedure
1. Disconnect the EGR vacuum line currently on port "J" on the front of the TBI unit. See Figure No.1.
2. Install connector bleed assembly, P/N 10105820 on port "J" of the TBI unit.
3. Reconnect the EGR vacuum line removed from port "J" to the open end of the connector bleed assembly.
Labor Operation Labor
Number Time Description
T7455 .3 Hr Identify existing PROM and install connector bleed
assembly.
Add .2 Hr To change PROM if necessary.