What does it mean?
As you know, the internal combustion engine does not burn liquid fuel, but fuel vapors. To extract the most power out of each drop of fuel, it needs to be sufficiently vaporized inside the engine, so it can be ignited. To achieve sufficient fuel vaporization, most port fuel injection systems work at moderate pressures, 35-75 psi. The pressure and spray, in combination with high intake and cylinder temperatures, helps the fuel to vaporize even better, for better power output and fuel economy.
Diesel engines and some modern gasoline engines use a different form of fuel injection, injecting fuel directly into the cylinder. Because the fuel is injected in the compression stroke when cylinder pressure is approaching maximum, the fuel injectors need to run at much higher pressures. An electric fuel pump, mounted in or near the fuel tank, supplies fuel to a mechanical fuel pump, usually mounted directly to the engine. The mechanical pump boosts the pressure for the direct injection system.
Most gasoline direct injection (GDI) systems run up to 2,500 psi, and most diesel injection systems run over 4,000 psi. A direct injection fuel system’s basic components include a high pressure fuel pump, fuel rail, injectors and a custom programmed engine control module. (6/10/2011) To properly meter fuel injection, the engine control module (ECM) closely monitors and modulates the high pressure system, even between injector pulses.
If the ECM detects an unexpected drop in pressure in the high-pressure side of the fuel system, anywhere between the mechanical fuel pump and the fuel injectors, it will set a diagnostic trouble code (DTC), P0093 “Fuel System Leak Detected – Large Leak,” and illuminate the check engine light (CEL).