A direct High Pressure Injection Pump can’t increase its speed independent of the engine to increase it’s output or pressure, so it has to control the volume of fuel that is compressed. This relationship is what makes direct injection high-pressure fuel pumps a mystery to some technicians and even engineers. But once you understand the relationship between the pump and control solenoid, your diagnostic skills will grow.

A direct injection fuel pump can’t increase its speed independent of the engine to increase it’s output or pressure, so it has to control the volume of fuel that is compressed. This relationship is what makes direct injection high-pressure fuel pumps a mystery to some technicians and even engineers. But once you understand the relationship between the pump and control solenoid, your diagnostic skills will grow.

High-pressure fuel pumps are mechanical and are typically driven by a camshaft. A lobe on the camshaft pushes on a follower or roller that moves a piston. The piston in the pump has two cycles, suction and compression. The solenoid on the side of the pump controls how much fuel is compressed during the compression ***. During the suction cycle, the solenoid will allow fuel from the low-pressure side of the fuel system to enter the pump. As the piston starts to travel upwards, the solenoid will remain open. The fuel is pushed into the low-pressure side of the fuel system when the solenoid is open. When the solenoid is shut, the low-pressure and high-pressure side of the fuel system are isolated.

If there is low demand on the engine, the solenoid will remain open longer and a smaller volume of fuel is compressed. If there is a high demand on the engine, the solenoid will close sooner, and a higher volume of fuel will be compressed. The length of time the solenoid is open will determine how much fuel reaches the fuel injectors.

The operation of the solenoid is engine-position dependent. The ECU and pump use the camshaft position sensor to know the position of the pump’s lobe on the camshaft. With engine position information, it can accurately time the events of the solenoid on the high-pressure fuel pump.

If you hook up a scope to the solenoid, you will see a “peak and hold” signal that will change as demands on the engine change. On channel B, you can graph the camshaft position sensor to understand the location of the lobe.

What If?

The supply pump in the tank also can work as a limp-home pump if the high-pressure pump fails on some engines. When this happens, it will increase the output of the supply pump, open the solenoid on the high-pressure pump and change the open times of the injectors. This engine will have restricted performance. If the supply pump is weak or failing, it has been observed on some vehicles that the suction from the high-pressure fuel Injection Pump Machine can *** fuel from the tank and keep the vehicle running, but with a great loss of power.

Diagnostic fundamentals for GDI are not that much different than conventional fuel injection systems. These systems inject the right amount of fuel directly into the cylinder. These systems are very efficient and are able to get the right amount of fuel into the cylinder so no fuel is wasted by not having to spray on the back of the intake valve.