How Direct Fuel Injection Works
Direct injection is one of the newest gasoline fuel systems available. Mitsubishi introduced DI systems for gas engines in 1996 and achieved higher power ratings and increased fuel economy. Unlike port injection (which injects fuel into a port above the cylinder), direct injection bypasses the intake valve and shoots atomized fuel directly into the cylinder. This, in theory, maximizes the efficiency of the engine cycle and allows precise fuel system tuning by the ECU.
Direct injection itself is nothing new; we’ve been using it on diesel engines for decades. What is new is the prolific adoption of direct injection on gasoline engines, especially when combined with complex emission-control systems.
Prior to 2008, vehicles equipped with direct injection made up less than 3% of new car sales in the United States. Today, that number has ballooned to over 50% due (in part) to increased government fuel economy standards. But has the new system caused more problems than it has prevented? With ten years of hindsight, we say no; but there are some issues that engineers failed to prevent.
Problems with Gas D.I. Fuel Systems
In this article, we’ll focus primarily on the Chevy LT or ‘EcoTec3’ V6 and V8 engine family (sorry GM). Overall, this engine family has proven to be robust and reliable. But numerous consumer complaints have gained the LT-series engines a rocky reputation on the forums. Plus, I bought a Silverado equipped with the 5.3 EcoTec motor back in 2017, and I’m well versed in these issues. Here are two common problems that are unique to D.I. fuel systems.
One of the most common complaints about the new LT engines is a constant ticking that people mistake for an exhaust leak or lifter noise. It’s not technically a problem, but it drives many conscious consumers crazy at idle.
Such sounds were once indicative of a problem, and are therefore worth addressing. The ‘EcoTick’ is a direct result of the new direct-injection system. The noise is caused by the injectors themselves, which run on a high-pressure rail system, similar to a diesel engine.
• Carbon Fouling
Another issue with direct injection engines is the tendency for valves to foul up with carbon. This problem is normally avoided in carbureted and port-injection engines because the valves are cleaned when fuel passes over them. Gasoline acts as an antifoul agent in typical engines but never touches the modern D.I. systems’ intake valve.
• Higher Costs
The high-pressure fuel system required by direct injection poses new challenges for manufacturers and mechanics. High-pressure systems are notoriously difficult to perfect, and they cost more to maintain and repair. However, companies like Bosch have mastered designing these systems, and outsourcing helps automakers reduce costs and complexity.
Is Direct Injection Worth It?
Direct injection is absolutely worth it from a practical standpoint. It’s a clear step in the evolution of gasoline engine design and provides notable benefits in both tuning and efficiency. And even though this system’s early years may be imperfect, we still think the benefit outweighs the costs. Over time, automakers are sure to work out the kinks and increase the reliability of these systems (which are already quite dependable).
About THE AUTHOR
I rebuild & restore classic cars and trucks when I'm not researching and writing about all things automotive. My current project is a 1978 Ford.Read more about Joshua Weinstein