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High Pressure Fuel Pump Test

  1. Check fuel tank(s) for adequate fuel supply, do not assume fuel gauge is correct. Check for fuel leakage at all fittings and lines. To check for electrical continuity to fuel pump, locate fuel pump connector at rail mounted (high pressure) fuel pump. Disconnect connector from body wiring harness and connect a volt/ohmmeter (VOM) across body connector.
  2. With ignition off, measure resistance. If resistance is 5 ohms or less, go to step 4. If resistance is 5 ohms or more, connect lead of VOM to ground lead of body wiring harness and check for continuity to ground. If there is no continuity, repair wiring or body ground and repeat step 2.
  3. If there is continuity, attach VOM to Pink/Black H wire of body connector and check continuity to ground. If not okay, it will be necessary to check wiring at pump-sender. If wiring checks okay, check continuity across pump terminals. If not okay, replace pump-sender assembly. Check for a good connection at pump-sender connector.
  4. Set meter to read voltage and turn ignition on. Voltage should rise to 12 volts for one second and then return to zero. If voltage is not within specification, check electrical circuit and repair as required.
  5. Attach VOM to pump harness leads and check continuity across leads. If okay, go to step 6. If not, check at pump terminals. If not okay at pump terminals, replace pump.
  6. Check fuel pump pressure and flow as follows: with an assistant in vehicle, raise vehicle on a hoist and attach pressure gauge to fuel diagnostic valve. As a preliminary check, turn ignition on, and check pressure gauge reading. Gauge should read 30-40 psi if pump is operating properly and other system components are okay. Go to next step.
  7. Disconnect fuel return line at fuel rail. Use care to avoid fuel spillage. Connect hose from fuel rail fitting to a calibrated container of at least one quart capacity. Replace fuel pump relay with modified relay. See MODIFYING FUEL CUT-OFF RELAY  in this article. Take ground lead to a convenient location on vehicle and ground it. This procedure should run fuel pump. Energize fuel pump for 10 seconds.
  8. Allow fuel to drain from return hose into container and observe volume. Fuel pump is operating properly if fuel pressure reaches 35-45 psi, fuel flow is a minimum of 5.6 oz. in 10 seconds and fuel pressure remains a minimum of 30 psi immediately after de-energization.
  9. If all 3 conditions are met, fuel pump is operating normally. If conditions are not met, check for engine and electrical problems. If okay, go to next step.
  10. Check for engine and electrical problems. If fuel pressure meets specification but fuel flow does not, check for blocked filter(s), fuel supply lines, and/or tank selector valve. After correcting any blockages, repeat above tests. If fuel flow still does not meet specification, replace pump.
  11. If both fuel pressure and fuel flow meet specification but system will not stay pressurized after pumps are turned off, check for leaking injectors or regulator. If they are both okay, replace fuel pump. If no fuel flow or fuel pressure is observed, fuel system should be checked as in step 10. If system is okay, replace fuel pump.
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