This paper presents a new model-free adaptive full-order sliding mode control (MAFOSMC) approach for addressing the challenge of precise control for the high-pressure common rail system (HPCRS) in marine engines. First, the mathematical model of HPCRS is modeled based on the hydrodynamics and the problem statement is presented. The model-free control structure is designed by adopting time delay control (TDC) technology, which can estimate uncertain and unknown dynamics without exact priori information about the system. Furthermore, the continuous sliding mode controller is developed to exhibit features of high accuracy, strong robustness, fast response based on full-order sliding mode control (FOSMC), and improved power reaching law. Then, a bidirectional adaptive strategy was designed to handle the unmodelled dynamics and unknown disturbances. The stability analysis of the closed-loop system is conducted using Lyapunov theory. Overall, the experimental comparisons were conducted with traditional FOSMC under three different testing scenarios, validating the efficacy and benefits of the proposed MAFOSMC approach for marine engines.