Housing Pressure Altitude Advance - Operation

Number: 84-187

Section: 6E (VIt)

Date: Sept., 1984
Subject: HOUSING PRESSURE ALTITUDE ADVANCE


Model and Year: ALL 1984 VEHICLES WITH 4.3L AND 5.7L DIESEL ENGINES
TO: ALL CHEVROLET DEALERS


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 engine may stop running and it will not restart. An altitude car will drive normally at higher altitudes but may stop running when driven to a lower altitude.