ROUGH IDLE AND/OR CONVERTER ODOR (SERVICE PROCED.-NEW PROM

VEHICLES AFFECTED: 1988 C1,C2,K1 AND K2 TRUCKS W/4.3L (VIN CODE Z)

Some 1988 C/K-trucks equipped with 4.3L (VIN Code Z) engines may exhibit an exhaust odour often described as sulphur or rotten egg smell at idle following sustained highway driving or trailer towing. Additionally, some trucks may exhibit rough or unstable idle quality.

These conditions may generally be addressed by relocating the oxygen sensor from the left hand exhaust manifold to the exhaust takedown (Y-pipe) and installing the appropriate calibration PROM.

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

Quantity Description Part Number -------- ----------- ----------- 1 Exhaust Y-pipe 15620225 1 Plug 10017198 2 Seal 15522434 1 Calibration PROM See Application Table

Parts are currently available.

SERVICE PROCEDURE:

1) Disconnect the battery

2) Remove the exhaust Y-pipe and discard.

3) Install new Y-pipe (P/N 15620225). It may be necessary to replace the exhaust manifold to Y-pipe seals (P/N 15522434) prior to installing the new Y-pipe.

4) Remove the oxygen sensor from the left side 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 the sensor to 3O ft/lbs.

5) Remove the wiring harness cover located at the rear of the engine, see Illustration.

6) Untape the existing oxygen sensor lead wire a short distance up the harness and reroute as shown in the Illustration. No splicing is necessary.

IMPORTANT: Assure that the lead wire does not contact the sharp edge of the dipstick tube bracket.

7) Install plug (P/N 10017198) in the former oxygen sensor location in the left side exhaust manifold.

8) Install the appropriate calibration PROM from the Application Table.

9) Reconnect the battery.

10) 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 oxygen sensor location, it may cause the exhaust odour and/or unstable idle quality conditions to continue.

Use appropriate Labour Operation. Labour Time ....1.4 Hrs.

APPLICATION TABLE

CURRENT SERVICE NEW TRUCK TRANS. EMISSIONS PROM ID. PROM PROM PROM ID. MODEL MODEL (RPO) PACKAGE (SCANNER) KIT P/N LABEL (SCANNER) ----- ----------- ------- --------- -------- ----- --------- C1,K1 A3 (M40) NA5/NA6 3491 16121150 AKRZ 3441 C2,K2 A3 (M40) NA5/NA6 3551 16121150 AKRZ 3441 C,K A3 (M40) NA5/NA6 2251 16121150 AKRZ 3441

C1,K1 A4 (MD8) NA5/NA6 3501 16121154 AKSB 3461 C2,K2 A4 (MD8) NA5/NA6 3481 16121154 AKSB 3461 C,K A4 (MD8) NA5/NA6 2261 16121154 AKSB 3461

C2,K M4 (M20) NA5/NA6 3471 16121166 AKSK 3521 C2,K M4 (M20) NA5/NA6 8411 16121166 AKSK 3521 C1 M4 (M20) NA5/NA6 8411 16121162 AKSJ 3511 K2,K100 53 M4 (M20) NA5/NA6 8951 16121166 AKSK 3521

C,K M5 (MG5) NA5/NA6 3451 16121158 AKSF 3491 C,K M5 (MG5) NA5/NA6 2271 16121158 AKSF 3491

NOTES:

TRUCK MODEL DESCRIPTION EMISSIONS PACKAGE DESCRIPTION ----------------------- -----------------------------

C = All C-trucks NA5 = Federal Emissions C1 = All C10-trucks NA6 = High Altitude Emissions C2 = All C20-trucks NB2 = California Emissions K = All K-trucks K1 = All K10-trucks K2 = All K20-trucks K100 53 = K10 w/Extended Cab

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.