Systems and methods for fuel injection

1. A system, comprising:

an engine including a cylinder;

a direct injection fuel pump including a piston, a compression chamber, a step chamber arranged below a bottom surface of the piston, a cam for moving the piston, and a solenoid activated check valve positioned at an inlet of the compression chamber of the direct injection fuel pump;

a first pressure relief valve fluidically coupled to the step chamber of the direct injection fuel pump, the first pressure relief valve biased to regulate pressure in the step chamber;

a second pressure relief valve positioned upstream of the solenoid activated check valve and fluidically coupled to the compression chamber of the direct injection fuel pump, the second pressure relief valve biased to regulate pressure in the compression chamber;

a lift pump fluidically coupled to the compression chamber through the second pressure relief valve and then the solenoid activated check valve from a low pressure passage of the lift pump, and coupled to the step chamber through the first pressure relief valve from the low pressure passage;

only one step room passage, the only one step room passage connected to the low pressure passage, the first pressure relief valve in the only one step room passage;

a compression chamber passage connecting the low pressure passage to the compression chamber, the solenoid activated check valve and the second pressure relief valve both in the compression chamber passage;

a direct injector fuel rail fluidically coupled to the compression chamber of the direct injection fuel pump; and

a direct injector providing fuel to the cylinder, the direct injector receiving fuel from the direct injector fuel rail.

2. The system of claim 1 , wherein the step chamber is pressurized during a suction stroke in the direct injection fuel pump, and wherein the step chamber is pressurized to a pressure higher than an output pressure of the lift pump during the suction stroke in the direct injection fuel pump.

3. The system of claim 2 , wherein the step chamber is substantially at the output pressure of the lift pump during a compression stroke in the direct injection fuel pump.

4. The system of claim 3 , wherein the compression chamber is pressurized during the compression stroke in the direct injection fuel pump, and wherein the compression chamber is pressurized to a pressure higher than the output pressure of the lift pump during the compression stroke in the direct injection fuel pump.

5. The system of claim 4 , further including a controller with computer-readable instructions stored on non-transitory memory for adjusting a status of the solenoid activated check valve to regulate pressure in the direct injector fuel rail.

6. The system of claim 5 , wherein the controller includes instructions for closing the solenoid activated check valve to increase the pressure in the compression chamber of the direct injection fuel pump to higher than a setting of the second pressure relief valve, the pressure increased based on a desired fuel rail pressure in the direct injector fuel rail.

7. The system of claim 1 , further comprising a third pressure relief valve arranged in parallel with the first pressure relief valve and a fourth pressure relief valve arranged in parallel with the second pressure relief valve.

8. The system of claim 1 , further comprising a third pressure relief valve arranged in parallel with the first pressure relief valve and a fourth pressure relief valve positioned along a passage coupling the only one step room passage to the compression chamber passage.

9. The system of claim 1 , further comprising a fuel passage connecting the only one step room passage to a low pressure fuel injection rail.

10. The system of claim 9 , further comprising a third pressure relief valve in the fuel passage connecting the only one step room passage to the low pressure fuel injection rail.