What is the difference between multi-point fuel injection and direct injection?
2 Answers
Multi-point fuel injection and direct injection differ in the following aspects: 1. Fuel injection method: Fuel injection can be categorized into conventional fuel injection, single-point fuel injection, and multi-point fuel injection. The forms of fuel injection are largely similar, as they all involve injecting fuel into the intake manifold where it mixes with air before entering the cylinder for combustion. However, the control precision has become increasingly refined. In contrast, direct injection delivers fuel directly into the cylinder, where it mixes with air from the intake manifold before combustion. This process eliminates intermediate steps, making direct injection another form of fuel injection. 2. Technology: Multi-point fuel injection has a relatively simple structure and more mature technology. The fuel injection pressure is not as high as in direct injection, so the requirements for electronic fuel injectors are lower, and the cost is relatively cheaper. In terms of reliability and maintenance, multi-point fuel injection is clearly more economical. Additionally, multi-point fuel injection engines have lower fuel quality requirements. The main advantage of direct injection lies in injecting fuel directly into the combustion chamber at extremely high pressure. With significant advancements in electronic control systems in recent years, the computer's ability to interpret and control air intake and fuel injection timing has become more precise, enabling stratified combustion and lean combustion. As a result, direct injection offers superior fuel efficiency and performance compared to multi-point fuel injection. 3. Carbon buildup: Multi-point fuel injection engines can form a mixture in the intake manifold, making it easier for carbon deposits to accumulate in the intake tract. However, since multi-point fuel injection sprays fuel into the intake manifold and gasoline itself is an effective carbon deposit cleaner, it can effectively clean components such as intake valves, cylinders, fuel injectors, and intake manifolds. Therefore, multi-point fuel injection engines generally have fewer carbon deposit issues compared to direct injection engines. Direct injection engines, on the other hand, inject fuel directly into the cylinder, making it easier for carbon deposits to form inside the cylinder (e.g., on the throttle valve). Additionally, the intake manifold in direct injection engines lacks sufficient gasoline to clean carbon deposits, leading to the accumulation of more carbon deposits over time. This can result in restricted airflow, increased fuel consumption, and reduced engine performance.
From my over ten years of experience in car repair, multi-point fuel injection sprays fuel near the intake manifold, waiting for air to mix in. This system is simple, reliable, and rarely fails, used in most older car models, and is cheaper to maintain. Direct injection is different—it sprays fuel directly into the cylinder for ignition, offering higher efficiency, stronger power, and better fuel economy. However, its design is more complex, and carbon buildup is a common issue. For example, residual oil in the cylinder over time can easily clog the fuel injectors, requiring regular cleaning. In daily driving, cars with direct injection feel more aggressive in acceleration, especially with strong push-back sensation at high speeds, while multi-point injection provides a smoother ride, suitable for owners who prefer hassle-free driving. During repairs, direct injection often brings more trouble, requiring specialized tools and higher costs, whereas multi-point injection is much simpler—just plug and unplug. In short, one follows a classic approach, while the other pursues performance upgrades. The choice depends on individual needs.
