Chart A7, Fuel System Diagnosis: Notes

If there are no RPM reference pulses, the ECM will shut off the fuel pump within 2 seconds after the key is turned on. The fuel pump test terminal is located in the left side of the engine compartment. When the engine is stopped, pump can be turned on by applying battery voltage to the test terminal.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Fuel pressure should be noted while fuel pump is running. Fuel pressure will drop immediately after fuel pump stops running due to a controlled bleed in the fuel system.
Low fuel pressure falls into 2 categories:
- Regulated Pressure Less Than 9 psi (62 kPa) - Amount of fuel to injectors is okay, but pressure is too low. Fuel system will be running lean and may set Code 44. Also exhibits hard starting cold and poor overall performance.
  
  Fig 1: Flow Chart A7 (1 of 2) - Trooper II (2.8L) Fuel System Diagnosis
  Courtesy of ISUZU MOTOR CO.
  
  Fig 2: Flow Chart A7 (2 of 2) - Trooper II (2.8L) Fuel System Diagnosis
  Courtesy of ISUZU MOTOR CO.
- Restricted Flow Causing Pressure Drop - Normally, a vehicle with a fuel pressure of less than 9 psi (62 kPa) at idle will not be driveable. However, if the pressure drop occurs only while driving, the engine will normally surge, then stop, as pressure begins to drop rapidly.
Restricting the fuel return line allows the fuel pump to develop its maximum pressure (dead head pressure). When battery voltage is applied to the fuel pump test terminal, pressure should be 13-18 psi (90-124 kg/cm² ).
This test determines if the high fuel pressure is due to a restricted fuel return line or a throttle body pressure regulator problem.