How Gen V Direct Injection works

The all conquering supercharged LT4. Drawing by David Kimble

GM’s Gen V engines use direct injection which requires a proper fuel supply. There’s a lot of misunderstanding about the fuel delivery system because most enthusiasts are not familiar with PWM (Pulse Width Modulated) style fuel pumps.

The Overview:
For daily driving, you would normally see the engine target the stoichiometric AFR (Air Fuel Ratio) of 14.7:1 (also referred to as Lambda), if you have a wideband gauge hooked up. However, with 10% ethanol in most pump gas today, you see the program setup for 14.1:1 to account for that blend. When you step on the pedal and go wide open throttle (WOT), the vehicle goes into what is called “PE Mode” or “Power Enrichment Mode” looking for values approximately 12:1. This defers to another table that has modifiers of your aforementioned stoichiometric AFR values. The Mass Air Flow (MAF) tables and the Dynamic Airflow (VE) or volumetric efficiency tables that provide the basis for the manipulated fueling requested, taking into account factors like injector size in lbs/hr, the requested fuel line pressure and the Start Of Injection (SOI) which tells the injector when to fire.

Cross-section shows the direct injection of fuel into the combustion chamber

How it works:
The system uses two fuel pump technologies. The low side in-tank pumps are the pumps in the fuel tank that are controlled by the Fuel Pressure Control Module (FPCM) also called Fuel Pump Pressure Module (FPPM) for power output to the high pressure fuel pump which then supplies the fuel rails. The system requests approximately 50 PSI during normal driving and jumps up to approximately 72 PSI when going WOT.

The High Pressure Fuel Pump (HPFP) is located under the supercharger on the valley of the engine, in-between the cylinder heads. The high pressure pump has command technology which references it’s position as the plunger rides up and down on a specifically ground lobe on the camshaft to pressurize the fuel as it goes through the pump producing up to 2,900 psi fuel pressure (similar to diesel technology).

Factory bent high-pressure lines in the plenum. High Pressure fuel pump is shown right above the flex plate between cylinders 7 & 8.

The pressurized fuel enters the CNC (Computer numerical control) bent fuel lines and travels to the rails, and then enters the injectors. These injectors, unlike previous years port injection are located in the cylinder head with the tip projecting into the combustion chamber. Since the engines are direct injected, the fuel is fired into the cylinder from 1,500 -2,900 PSI on the intake stroke for a very short period of time (5 mil-seconds). The injected fuel will vaporize before the piston reaches top dead center (TDC), which allows for much more predictable fueling and more accurate/higher target AFRs . The benefits are less wasted fuel, better fuel delivery and a better AFR potential which results in increased mileage and reduced emissions.

For more detailed information on Gen V fuel delivery issues please ready my recently updated Gen V installation guide located here: