What this test proves

Measure pressure decay after shutdown. Decay alone cannot identify which component leaks.

Tools

  • Fuel-compatible rated pressure tester
  • Timer
  • Fuel-system diagram and hold-pressure specification

Preparation and precautions

  • Use the specified low-pressure circuit and approved depressurization procedure.
  • Do not clamp plastic, braided or high-pressure fuel lines. Never loosen a running high-pressure connection.

Connections

  • Attach the approved tester at the low-pressure test point. Check the tester and adapter themselves for leaks.

Equipment settings

  • Correct pressure units; record starting pressure and elapsed time against the OEM hold specification.

Test sequence

  1. Build pressure using the prescribed pump command or engine operation.
  2. Stop the pump/engine as directed and begin timing.
  3. Record pressure at the specified intervals.
  4. Use only the approved isolation procedure to distinguish injector, regulator, check-valve or plumbing leakage.
  5. Restore and leak-check the system.

Expected signal / readings

Pressure decay must meet the vehicle’s allowed amount over its defined time; some systems intentionally release pressure.

Interpreting results

  • Rapid loss can originate in the tester as well as the vehicle.
  • Combine decay with starting symptoms and the OEM isolation results before replacing a component.

Common mistakes

  • Using a universal hold time
  • Diagnosing an injector from decay alone
  • Pinching an unsuitable line