Exhaust - Odor (Rotten Egg Odor At Idle)
88chevy13GMC NUMBER: 88-T-126
GROUP: 6E - Engine Emissions
DATE: JULY, 1988
CORPORATE
NUMBER: 836523
SUBJECT: EXHAUST ODOR (ROTTEN EGG ODOR AT IDLE)
MODELS: 1988 M VAN WITH 4.3L (VIN CODE Z) ENGINES
Some 1988 M vans equipped with 4.3L (VIN Code Z) engines built prior to 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 APPROPRIATE CALPROM.
PARTS REQUIRED
0TY DESCRIPTION PART NUMBER
1 exhaust Y-pipe 15598249
1 plug 10017198
1 the appropriate PROM from the table
below
CALIBRATION PROM TABLE
Federal/Altitude Emissions Packages (NA5 and NA6)
SERVICE PROCEDURE
1. Disconnect the battery.
2. Check to determine if a bleed connector 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 connector when relocating the oxygen sensor to the Y-pipe because the air bleed will result in artificially 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 40 N-m (30 ft.lbs.) It will be necessary to remove the wiring harness cover and untape the existing O2 sensor lead a short distance up the hamess. 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, in the former oxygen sensor location in the left exhaust manifold and torque to 40 N-m (30 ft.lbs).
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 O2 sensor location, it may cause the exhaust odor condition to continue.
Labor Operation: T7620 Labor Time: .9 hr