The sole point of a diesel is to run on oil. That's why the compression is normally high. It takes alot of compression to ignite diesel. Notice if you see someone accidentally fill their tanks with diesel, what happens? Doesn't run to save it's life, right? The glow plugs initially is just a hot spot in the CC that ignites the fire. After that, it runs off it's own detonation. Fuel the fire and it increases it's idle. With the direct injection, it justs make it easier to control fuel to get better mileage and aids in the benefit of better tailpipe emissions. I would so love to hear someone's opinion on that. Reps for all those that has chimed in on this