DIESEL ALTITUDE ADJUSTMENTS ADJ. TO IMPROVE PERFORMANCE

1983 Cutlass Supreme models equipped with 4.3L V-6 diesel engines will be manufactured with either high or low altitude diesel emission systems. Cars equipped with the high altitude emission system will be invoiced with option NA6. The type of system can also be identified by the emission label attached to the fan shroud. The label will indicate that the car was built for primary use at either high or low altitude. These procedures are considered altitude performance adjustments and apply only to in-use vehicles. They should not be used to modify vehicles prior to sale.

CONVERSION OF LOW ALTITUDE SYSTEM TO HIGH ALTITUDE

Dealers in high altitude areas should encourage owners who have moved to high altitude counties to purchase the following adjustment procedure. This adjustment is considered an owner maintenance expense. See attachment for a list of counties which the Environmental Protection Agency has designated as high altitude counties. Diesel timing should be checked or adjusted at the same approximate altitude at which the vehicle will be driven.

1. Replace the EGR vacuum control valve assembly with the assembly shown in Figure 1. Refer to Parts Information for part numbers.

2. Install Timing Meter J-33075 or equivalent, set pump Timing to -6 DEG, and set engine idle to specifications, turn off engine.

3. Remove air crossover assembly. Install screen covers J-29657.

4. With transmission in Park and A/C off, start engine.

5. Loosen locknut (Figure 2) and slowly turn metering valve stop screw clockwise until idle speed drops approximately 10 RPM.

6. Turn metering valve stop screw counterclockwise exactly 2 1/8 turns. Tighten locknut.

7. Check for fuel leaks around metering valve stop screw.

8. Turn engine off.

9. Remove magnetic tachometer probe and screened covers from intake manifold and reinstall parts removed.

10. Fill in dealer code and date on the supplemental emission control label, part number 14057201 or equivalent (Figure 3). This label must be placed next to the existing underhood emission control information label. Wash off the area with soap and water, dry thoroughly, and apply the new label.

PARTS INFORMATION

Part Part Number ---- ----------- 1. EGR Vacuum Control Valve Assembly 22519396 or equivalent High Altitude Application

2. Label 14057201 or equivalent

Suggested Time

The suggested time to perform the Low to High Altitude Adjustment and part replacement is 0.8 hour labor.

CONVERSION OF HIGH ALTITUDE SYSTEM TO LOW ALTITUDE

Dealers should advise owners moving to low altitude areas that they should purchase the following altitude adjustment procedure. This adjustment is considered an owner maintenance expense. Diesel timing should be checked or adjusted at the same approximate altitude at which the vehicle will be driven.

1. Replace the EGR vacuum control valve assembly with the assembly shown in Figure 1. Refer to Parts Information for part numbers.

2. Install timing meter J-33075 or equivalent, set pump timing to -6 DEG, and set engine idle to specifications, turn off engine.

3. Remove air crossover assembly. Install screen covers J-29657.

4. Loosen lock nut (Figure 2) and turn metering valve stop screw counterclockwise 1.5 turns. Tighten lock nut.

5. Start engine. With engine running and transmission in Park, check for fuel leaks around metering valve stop screw.

6. Turn engine off.

7. Remove magnetic tachometer probe and screened covers from intake manifold and reinstall parts removed.

8. Fill in dealer code and date on the supplemental emission control label, part number 14055121 or equivalent (Figure 4). The label must be placed next to the existing underhood emission control information label. Wash off the area with soap and water, dry thoroughly and apply the new label.

PARTS INFORMATION

Part Part Number ---- ----------- 1. EGR Vacuum Control Valve Assembly 22519395 or equivalent Low Altitude Application

2. Label 14055121 or equivalent

Suggested Time

The suggested time to perform High to Low Altitude adjustment and part replacement is 0.8 hour labor.

COUNTIES WHICH ARE DESIGNATED HIGH-ALTITUDE AREAS

ARIZONA MONTANA UTAH

Apache Navajo Beaverhead Madison Beaver Morgan Cochise Yavapai Deer Lodge Meagher Box Elder Piute Coconino Gallatin Park Cache Rich Jefferson Silver Bow Carbon Salt Lake COLORADO Judith Basin Wheatland Daggett San Juan Powell Davis San Pete Adams Kit Carson Duschesne Sevier Alamosa Lake NEBRASKA Emery Summit Arapahoe LaPlata Garfield Tooele Archuleta Larimer Banner Kimball Grand Unitah Boulder Las Animas Cheyenne Sioux Iron Utah Chaffee Lincoin Juab Wasatch Cheyenne Mesa NEVADA Kane Wayne Clear Creek Mineral Millard Weber Conejos Moffat Carson City Lyon Costilla Montezuma Douglas Mineral Crowley Montrose Elko Nye WYOMING Custer Morgan Esmeralda Pershing Delta Otero Eureka Storey Albany Natrona Denver Ouray Humboldt Washoe Campbell Niobrara Dolores Park Lander White Pine Carbon Park Douglas Pitkin Lincoln Converse Platte Eagle Pueblo Fremont Sublette Elbert Rio Blanco NEW MEXICO Goshen Sweetwater El Paso Rio Grande Hot Springs Teton Fremont Routt Bernalillo Mora Johnson Vinta Garfield Saguache Catron Rio Arriba Laramie Washakie Gilpin San Juan Colfax Roosevelt Lincoln Weston Grand San Miguel Curry Sandoval Gunnison Summit DeBaca San Juan Hinsdale Teller Grant Sans Miguel Huerfano Washington Guadalupe Santa Fe Jackson Weld Harding Sierra Jefferson Hidalgo Socorro Lincoin Taos IDAHO Los Alamos Torrance Luna Union Bannock Franklin McKinley Valencia Bear Lake Fremont Otero Bingham Jefferson Blaine Lemhi OREGON Booneville Madison Butte Minidoka Harney Lake Camas Oneida Klamath Caribou Power Cassia Teton TEXAS Clark Valley Custer Jeff Davis Hudspeth Parmer

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.