Housing Pressure Cold Advance (HPCA)

The HPCA is used to improve cold starting and emission control. Located in the top of injection pump, the solenoid advances injection timing by about 3-4° when engine is cold. Timing is advanced by decreasing housing pressure. At the same time, fast idle solenoid is activated. The HPCA solenoid is controlled by a temperature switch on the left rear head bolt of C Series with internal EGR and by the electronic control module in all others. The HPCA housing pressure regulator, located in the pump cover with an additional fitting that adapts it to the fuel return pipe, is adjustable. See Adjusting the HPCA in this article.