Most common is a lube line cracking and spraying oil all over the turbo.
"Another cause on the early AC4400CW's and Dash 9's was the fuel injection system would inject excess fuel if the engineer throttled up too quickly. What resulted was a lot of unburned fuel going up the stack. As the turbo spooled up, the exhaust temperature would get hot enough to ignite the unburned fuel in the stack, often resulting in a brief, but multi-foot-high flame from the stack. If this happened in a tunnel or under and underpass, it would typically scorch the paint on around the stack of the locomtotive and often considerably down the side of the hood."Most recently were GEVO's (the early ones) sending pistons flying out of the long hood. Crews were warned not to stand on the walkways when the engines where under load. Just my luck while railfanning in Marion, Ohio I had two of these things start up right next to me. This is a Dash 9, but it was basically the same thing:
http://talk.newagtalk.com/forums/thread ... 5#M1190655