Injection Pump - Housing Pressure Altitude Advance
Number 84-6 (Diesel)-15 Date 7/84Subject: HOUSING PRESSURE ALTITUDE ADVANCE - 1984 4.3L V-6 & 5.7L V-8 DIESEL ENGINE
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.