[Doby454]

Saw this post and recalled one from my Ford work site a while back-it's pretty good...

Posted on June 16 by Greg Holekamp: A diesel runaway is when the engine rpm goes up uncontrolled and there is no way the engine can stop itself. Diesel engines don't actually require any controls on then to run. All they need is fuel and air. Gas engines need a spark at just the right time, and a fuel pulse of just the right duration to run. Also, diesels can run on a wide range of fuel. Remember when all of us diesel guys were complaining about leaking injectors on 03's that were filling the crankcase with fuel? Well, 30+ quarts of a fuel/oil mix in the crankcase will submerge the crank. One of the last steps on the diesel diag sheet is an oil aeration test where you have to run the engine at wot (3500 or so rpm) for 3 minutes and then view the oil condition. That crank whipping up the fuel/oil will make a foam that rises through the engine, and eventually starts getting drafted into the intake stream. If there is enough coming into the intake, the engine rpm will start to rise even higher. Of course, this causes the oil to whip more, which makes it rise faster in the engine - a vicious cycle. You cut the key off, but the engine doesn't care - it's getting it's own fuel from another source. Smoke starts to pour from the tailpipe, and the truck starts to vibrate. At about 6000 rpm the ground starts to shake throughout the shop and the sales department looks outside to see if a thunderstorm is coming. 7500 rpm has the shop evacuating - by this time, the whole shop is flooded with smoke. 9000 rpm brings ominous noises from the shop - a cyclic wave of sound that feels like an invisible hand pressing on your chest. Somewhere about 10,000 rpm and the engine gives up. A sound that is a combination of a nearby lightning strike and every toolbox in the shop turning over at once explodes from the shop. The sound echos and continues for several seconds. You can actually feel a shockwave disperse through the concrete you're standing on. And then, the deafening silence. You try to see through the smoke and locate the truck - but something is wrong. It is sitting at an angle, tilted down in the front. And then you see why - both front tires are blown out. There is a scattering of parts 3 bays in each direction. A puddle of fluid is rapidly spreading from under the shredded front cap. The hood and fenders are destroyed, but ironically, the grille and headlights are still intact. And your first thought is - at least I don't have to work on this one anymore! And that, my friend Bernie, is a diesel runaway.