Chart C-7 HPAA/AFL Electrical Check: VIN N (5.7L) VIN T (4.3L)

Fig. 068 - WIRING DIAGRAM for Chart C-7 HPAA/AFL Electrical Check. VIN N, VIN T:

CHART C-7

HPAA/AFL ELECTRICAL CHECK

4.3L VIN "T"

5.7L VIN "N"

The housing pressure altitude advance (HPAA) solenoid is located in the fuel return line from the fuel injection pump to the tank. It's function is to regulate pump housing pressure, resulting in injection timing modification, according to altitute requirements. The HPAA is ECM controlled and is energized whenever the MAP sensor signals the ECM a barometric altitude reading representing about 4,000 ft. (1219 m) or more. The HPCA must be activated along with HPAA so that proper housing pressure (injection timing) modification can occur. An altitude fuel limiter (AFL) is mounted through the end of the injection pump housing. The AFL is a ECM controlled solenoid with a normally extended plunger which, upon AFL activation, retracts limiting the travel of the metering valve at wide open throttle. Both the HPAA and AFL are supplied with ignition voltage whenever ignition switch is on. Both are also energized by the same ECM terminal "L", which completes their ground circuit whenever altitude compensation is required.

Fig. 067 - Chart C-7 HPAA/AFL Electrical Check.:

This chart is to be used for HPAA and AFL electrical diagnosis only. Housing pressure, injection timing and fuel control diagnostics are covered in Section 6C5.
1. Checks for available ignition voltage feed through HPAA or AFL solenoid and checks for ground on circuit from ECM terminal "L" to solenoids. With MAP sensor electrical connector disconnected, and jumper installed between terminals "B" and "C", a low altitude environment is simulated and solenoids should be de-energized (extended). Test light should be "ON".
2. By disconnecting each solenoid one at a time and observing test light, the possibility of one open solenoid is checked.
3. Removing jumper wire and leaving MAP sensor disconnected simulates an altitude of over approximately 4,000 ft. (1219 m) Both solenoids should be energized (retracted), and test light "OFF".
4. This step determines if problem is faulty ECM, circuit or solenoids.