DIESEL ALTITUDE ADJUSTMENT ADJ. TO IMPROVE PERFORMANCE

MODELS: 1983 CABALLEROS WITH RPO LF9 5.7L V-8 DIESEL ENGINES

The 1983 GMC Caballeros with RPO LF9 5.7L V-8 diesel engines will be manufactured with either high or low altitude diesel systems. A vehicle with a high altitude 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 vehicle was designed for principal use at either high or low altitude.

These adjustments are considered Altitude Performance Adjustments and apply only to in-use vehicles. They should not be used to modify vehicles prior to sale.

Dealers must not sell vehicles with low altitude systems for principal use at high altitude.

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 service adjustment procedure out- lined below, which is considered an owner mainte- nance 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 (Figure No. 1) with the assembly shown in the parts information.

2. Install timing meter J-33075 or equivalent, set pump timing 4 DEG, and set idle speed to specifications.

3. Remove air cleaner and air crossover assemblies and install screen covers J-26996-2.

4. Install shop towel in the intake manifold valley area under the injection pump head to absorb any fuel leakage. Remove housing pressure tap plug and seal located on the rear of the pump (Figure No. 2).

5. Using the parts continued in kit, part number 22516487 or equivalent, assemble locknut and new seal (O-ring) to metering valve stop screw.

6. Install assembly in injection pump until lock-nut contacts pump housing. Tighten locknut.

7. Place transmission in Park, turn A/C off and start engine.

8. Loosen locknut and slowly turn metering valve stop screw clockwise until idle speed drops approximately 10 RPM.

9. Turn metering valve stop screw counterclock-wise 2-1/2 turns and tighten locknut.

10. Check installation for fuel leaks and remove shop towel from intake valley.

11. Turn engine off.

12. Remove timing meter and screened covers from intake manifold and re-install parts removed.

13. Type or print with ball point pen the dealer code and date in the space provided on the supplemental emission control label, part number 14057201 or equivalent, Figure No. 3 (part of kit). The label must be placed next to the existing underhood emission control information label to the extent possible. The label should not be affixed to any equipment that can be easily detached from the vehicle. Wash off the area with soap and water, dry thoroughly, and apply the new label.

PARTS INFORMATION

Part Part Number

1. EGR Vacuum Control 22515542 or Valve Assembly High equivalent Altitude Application - All Models

2. Kit Contents 22516487 or equivalent

Part Quantity

Locknut 1 Seal 1 Metering Valve Screw 1 Label part number 1 14057201 or equivalent (See Figure No. 3)

CONVERSION OF HIGH ALTITUDE VEHICLES TO LOW ALTITUDE

Dealers should advise owners moving to low altitude areas that they should purchase the service adjustment procedure outlined below which is con- sidered 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 (Figure No. 1) with the assembly shown in the parts information.

2. Install timing meter J-33075 or equivalent, set pump timing -4 DEG, and set idle speed to specifications.

3. Remove timing meter.

4. Type or print with ball point pen the dealer code and date in the space provided on the supplemental emission control label, part number 14055121 or equivalent (Figure No. 4). The label must be placed next to the existing underhood emission control information label to the extent possible. The label should not be affixed to any equipment that can be easily detached from the vehicle. Wash off the area with soap and water, dry thoroughly and apply the new label.

PARTS INFORMATION

Part Part Number 1. EGR Vacuum Control 22514746 or Valve Assembly Low equivalent Altitude Application - All Models

2. Label 14055121 or (See Figure No. 4) equivalent

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.