Trouble Shooting Any Diesel or Gasoline Fuel System

Any diesel or gasoline internal combustion engine requires fuel delivery (flow & pressure) to run. Although many different types of systems, they are all similar in basic fuel delivery. Most systems have some sort of low-pressure pump that supplies fuel at a low 3-80 psi to the main source of delivery at a higher pressure to the combustion chamber via some form of injector or carburetor device to deliver and atomize the fuel.

The first step in any diagnosis is to verify fuel at the adequate pressure for the specific engine after the fuel transfer or lift/supply pump. These pumps are either electric or mechanical, and can be in the fuel tank, or externally close to the tank (electric supply pump), or a mechanical pump mounted on the engine and run via a cam, or in some cases, a gear pump mounted on the actual diesel fuel injection pump or built inside the fuel injection pump.

Verifying fuel pressure and flow is straightforward with electric pumps. By disconnecting the output of the supply pump, fuel pressure/flow can be seen and measured. If no flow/ pressure is present, verify that the pump has the correct voltage. Many problems arise with the electrical wiring, fuses, or relays, preventing the pump to produce pressure/flow.

In some cases, the pump may be working, but there's a blockage of the screen filter in the tank. we have had instances where we had to apply air pressure to the line going to the tank to "blow-off "the plugged filter in the tank. If this is the case, removing and cleaning the tank will be necessary. There are several tank-mounted designs, some have multiple filter screens that can be plugged, but also can be cleaned and reused. This is especially relevant to diesel engines, as they are much more susceptible to algae growth in the tank.

The same method of checking delivery/ pressure can be used with the externally mounted mechanical pumps in the engine compartment. The gear-type pumps built internally with the diesel fuel injection pump can only be checked with very specialized equipment when the fuel injection pump is being remanufactured and in the testing phase. At AMBAC, every type of fuel injection pump is thoroughly tested during the remanufacturing process to make sure it meets or exceeds the OEM specification. As the official remanufacturer of all the US Marines Diesel equipment, AMBAC prides itself on our rigorous standards.

Once fuel/ pressure is verified to be within OEM specifications, we can rule out the supply/lift/transfer/rail pump as part of the problem, and move to the actual fuel injection or delivery system for the next phase in troubleshooting(see troubleshooting fuel systems blog).