engine trouble??

[98slushbox]

A friend of mine has an 06 4dr sb g56 with smarty and tst with a stock charger yet. He has sled pulled it a few times and was pulling last sat. and got to about 250ft and there was a pop and started missing and smoking funny. He hauled it home and pulled the inj. and found that number 5 was all carboned up and had a piece of carbon stuck on the tip covering part of the tip. Could this have been an inj. hung open or has anyone experienced this before? thanks