DIESEL HOUSING PRESSURE COLD ADVANCE INFORMATION

All 1984 model diesel engines except those sold in California contain a housing pressure altitude advance (HPAA) located in the fuel return line. Its purpose is to change the housing pressure as the car changes altitude.

The HPAA solenoid has an arrow stamped on the case and it is labeled "This end towards pump." This means put that end towards the injection pump. If the printing is no longer legible, refer to the service manual for proper orientation. Care must be exercised during service to make sure that the HPAA does not get reversed. If this were to happen, a Federal car will drive normally until it is driven to a high altitude. When the switch closes, the vehicle may experience a driveability condition and will not restart. An altitude car will drive normally at higher altitudes but may experience a driveability condition when driven to a lower altitude.

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.