A diesel engine that runs rough or not at all could be caused by fuel delivery problems. Most modern diesel engines have electronic controlled fuel systems. Older fuel systems used a mechanical fuel High Pressure Injection Pump.

　　Fuel delivery problems can cause low power, rough running, or the engine will not start at all. Before doing any fuel delivery diagnosis, the injectors and fuel filters should be checked also. A failing injector will also cause rough running.

　　The injection pumps on modern trucks usually equipped with a quick connect fitting on them or in the high pressure line to be tested. If you cannot find a fitting, you will have to hook your fuel pressure gauge in series with the high pressure line.

　　Your fuel pressure gauge should be rated at least 40,000 PSI. Common rail fuel systems use very high pressures for better fuel delivery and atomizing of the fuel. Fuel system problems are usually caused by dirty fuel or dirt entering the the fuel system.

　　Injection pumps rarely fail unless something causes it to fail. All checks should be made before condemning the injection pump. There is another way to see if the injection pump is failing and see if you have another problem.

　　If you have a scan tool, you can do an injector drop on each cylinder while watching fuel pressure PID. If engine RPM stays the same on one cylinder, the problem is mechanical or the injector itself. Next you should always do electrical checks.

　　If the engine has an electronic fuel pump, make sure the power and ground to the pump are good while the engine is at a higher RPM. This will command the fuel pump to work harder and demand more fuel putting a load on the circuit.

　　Low fuel pressure problems are most common in cold seasons or in cold places. Ice crystals can form in the fuel filters and diesel fuel can freeze if additive is not used. This can also happen in the injection pump.

　　Though all fuel injection pumps do fail, basic checks can be done first before replacing. The most conventional way to eliminate a fuel injection pump issue is to confirm your fuel pressure reading and compare with manufacturer specs.

　　Symptoms of a fuel injection pump failing are rough running, no power, extended cranking before starting, excessive smoking, misfires, or a no start issue. I have also seen electrical problems.

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