A mechanical diesel injection pump is designed to pressurize, meter, and distribute the diesel fuel that’s injected into the engine to create the optimum power output.

A mechanical injection system needs to be capable of pressurizing the plunger fuel sufficiently to open the injectors and deliver the fuel to the cylinders in an atomized form.

Fuel delivery timing is critical during all engine operating conditions and speeds. In a diesel engine, fuel is injected into the cylinder slightly before the piston completes its compression stroke. The objective of the injection pump is to match the operating conditions with the proper amount of fuel to create the desired air/fuel ratio.

The goal is to smoothly and evenly transmit force developed in the cylinders to the flywheel or torque converter. The job of the injection pump is to manage the nozzle cylinder pressure by injecting fuel and cause it to peak when the crankshaft throw angle offers little mechanical advantage, and to diminish as the crankshaft throw is driven to a 90-degree angle with the connecting rod when mechanical advantage is highest. Most diesel engines are engineered to attempt to produce peak cylinder pressure 10 to 20 crankshaft rotation degrees after TDC.

Fuel delivery timing is extremely critical in a diesel engine and impacts power, fuel economy, and emissions. If the injection timing is overadvanced, a loss of power will be experienced, along with possible internal engine failure such as piston damage. Excessive gray/black smoke can be a sign of an overly advanced pump setting. If the injection timing is retarded, a loss of power will result along with excessive smoke, high exhaust gas temperature, and if extremely late, severe white smoke.

It turns out that many of the symptoms of incorrect delivery valve pump timing are shared by timing the injection on either side of the optimum specification. For this reason, it may be very difficult to determine if the timing is advanced or retarded only by examining the exhaust color or the engine’s power output.