What this test proves

Check whether supply pressure follows demand when the complaint occurs.

Tools

  • Rated fuel-pressure transducer or approved remote gauge arrangement
  • Scan tool logging command, actual pressure and load
  • Approved load-test facility

Preparation and precautions

  • Confirm the system and pressure rating. For high-pressure rails use the separate rail-pressure scan-data guide.
  • Prefer a controlled workshop load test. Never route fuel or a mechanical fuel gauge into the cabin; do not watch equipment while driving.

Connections

  • Connect an approved low-pressure transducer at the specified supply point and secure its electrical logger away from heat and motion.

Equipment settings

  • Log pressure, pump command, engine speed and load together at a rate appropriate to the event.

Test sequence

  1. Establish the specified baseline.
  2. Reproduce the complaint only using a safe approved load procedure.
  3. Compare actual pressure with required pressure through the event.
  4. If it falls, check voltage at the pump, regulation and flow restrictions.
  5. Repeat the same conditions after repair.

Expected signal / readings

Pressure should follow the system’s required behavior without an unexplained collapse as demand rises.

Interpreting results

  • Pressure loss with normal pump command requires electrical and hydraulic checks.
  • A commanded reduction in pressure is not automatically pump failure.

Common mistakes

  • Assuming idle pressure proves load capability
  • Using unsecured test lines
  • Confusing scan-tool pressure units