Diagnosis of the fuel injection pump includes the following diagnostic steps (more detail for these checks can be found at the end of this section):
1. Check the fuel supply to the injection pump (refer to Figure 7-47):
– Check that the output of the lift pump is correct:
• Volume of at least 0.24 liter (1/2 pint) in 15 seconds
• Pressure of 40 to 60 kPa (5.8 to 8.7 psi)
– Check that the restriction of the fuel filter is not excessive:
• Lift pump volume and pressure should be present at the inlet of the injection pump.
– Check the fuel entering the injection pump for the presence of air, using a transparent hose:
• If air bubbles appear, check the lift pump suction line for air leakage under a vacuum.
– Check the quality of the fuel:
• If necessary, use a fuel with a known cetane rating.
2. Check the fuel return from the injection pump (refer to Figure 7-48):
– Check the injection pump housing pressure:
• If pressure is not within 55 to 83 kPa (8 to 12 psi), do one of these things:
– Check the return line for a restriction.
– Check the housing pressure regulator for a restriction.
– Check the fuel exiting the injection pump for the presence of air, using a transparent hose:
• If air bubbles appear, remove the injection pump for service.
3. Check the injection pump transfer pump pressure (refer to Figure 7-48):
– Pressure while cranking should be at least 138 to 207 kPa (20 to 30 psi).
– Pressure should increase as engine speed increases, and a maximum of over 690 kPa (100 psi) is possible.
4. Check the Housing Pressure Cold Advance (HPCA) solenoid operation (refer to Figure 7-49):
– With the engine at 2,000 rpm, jumper the fast idle/cold advance temperature switch to energize the HPCA solenoid circuit.
– Observe that the engine speed increases, indicating an advance in injection timing.
– If no change in engine speed occurs, diagnose the fast idle/cold advance circuit.
5. Check the injection pump automatic advance mechanism piston for movement (refer to Figure 7-49):
– With the engine at 2,000 rpm, press the lower end of the mechanical light load advance rocker arm toward the injection pump.
– Observe that the engine speed decreases, indicating a retard in injection timing.
– If no change in engine speed occurs, remove the injection pump for service.
6. Check the operation of the injection lines and nozzles (refer to Figure 7-50):
– Inspect the injection lines for external damage and evidence of fuel leakage.
– Replace any damaged injection line.
– Remove and test each injection nozzle for correct opening pressure, chatter, leakage and spray pattern (see page 7-60 for more information).
– Replace any faulty nozzle and install the nozzles with new compression gaskets.
7. If a fuel system fault still exists, remove the injection pump and send it to an authorized diesel injection pump repair shop.
