 In order to test the pressure in the fuel lines, you need a fuel pressure gauge and a place to attach it. Many manufacturers have installed a test fitting on the fuel rail for this purpose. If there is not a fitting there, you will have to install a “T” fitting in line. Most fuel injection systems require between 30 and 80 PSI to start and run the engine. Each application is different so be sure to check those manuals for fuel pressure specifications.
Fuel Pump Voltage Testing
Fuel pumps are electric, and if they aren’t powered properly, they can’t push enough fuel. To test this simply turn on the key, and place the leads of a voltage meter across the terminals of the pump. When the pump is inside the tank, test the current as close as possible to the pump. You may have to unplug the pump to measure it. If there isn’t enough power, check the ground, relays, and wiring harness.
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Static Pressure Test (car off key on or auxiliary powered)
Test for sustained pressure at manufacturer’s recommended PSI. ): Energize the fuel pump by turning on the key or connecting it to an auxiliary battery. Energized, the fuel pump should bring up fuel pressure very quickly and hold steady at a fixed value if there is no voltage at the pump,
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Residual Fuel Pressure Test
After completion of the static fuel pressure test above, the pump is turned off, or stops running. At this point the fuel delivery system should maintain it’s pressurized status. The manual has a specification for the duration and fall off of this pressure for several minutes. Check the manual for the specifications and compare it to your findings. If the fuel system pressure drops too quickly, this is a sign of a fuel leak that could result in a fire. Specifically look for the leak around the fuel pump check valve, along each of the fuel lines, the pressure control valves, and finally each of the fuel injectors.
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Fuel Volume Test
A fuel pump can pass the static and residual tests and still be BAD! If you suspect the pump, and it barely passes the first to tests, try a fuel volume test. This is the final manual check you can run without starting the engine on the vehicle. Measuring the volume of fuel the pump delivers in 30 seconds involves turning the engine off and allowing it to cool before connecting any test equipment. Then you connect a fuel flow gauge into the fuel supply line, or disconnect the fuel return line from the fuel pressure regulator. Connect a tube, hose, or fitting and direct the gas into a measuring container. Energize the fuel pump for 30 seconds. Generally speaking a quart of gas (~1 liter) in 30 seconds is adequate.
If you have passed these 3 checks, you are fairly sure you aren’t going to start the car on fire, have no leaks in the fuel system, and the pump works. Now you should run a few final checks to ensure that the fuel system is operational and full functional. Start that engine……..
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Engine @ Idle - Fuel Pressure Test
With the engine on, measure the fuel system pressure while the car is at idle and compare it to the manufacturer’s specifications.
Should the test fail to fall within specification, look for low voltage to the pump, worn pumps, plugged fuel filter, pinched or kinked fuel line, a bad pressure regulator or a nearly empty fuel tank.
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High Speed Fuel Availability Testing
Some folks call this Dead Head Pressure. The speed shops call it high speed fuel pump testing. Either way, the test is the same. Turn on the vehicle, and let it idle. Pinch off the fuel return lines and keep the vehicle at idle. The fuel pressure gauge should show at least 2 times the standard pressure. Without the higher output from the fuel pump you wouldn’t have enough pressure at higher RMP or Speeds. Replace fuel pumps that do not meet this standard.
Remember: If you diagnose a bad fuel pump and replace it. Inspect the inside of the fuel tank. The presence of rust or debris will lead to another premature fuel pump failure. Clean or replace the fuel tank to ensure the elimination of the problem.
Remember: New fuel pumps should always be installed with new O-rings, new debris screens, new fuel tank collar.
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Diesel Fuel Injector Parts Lookup |
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