High-pressure pumps generate and maintain fuel pressure for direct fuel injection systems in gasoline and diesel engines. Typically engine-driven, these positive displacement pumps deliver precise fuel volumes at pressures exceeding 300 bar (4,350 psi). Designs commonly utilize a cam-actuated piston, roller-cell, or gear mechanism to achieve high-pressure output. Integrated pressure regulators and pulsation dampeners are standard features. Modern units often incorporate electronically controlled actuators for variable pressure and flow delivery, optimizing engine performance and emissions. Failure manifests as hard starting, poor performance, or diagnostic trouble codes related to fuel pressure.