Loud Engine Noise problems of the 1998 Ford E-350

Original owner of 1998 Ford e350 extended-length XLT. At the time of the incident, the car had about 98,000 miles. I was at a stop light, the light turned green and I proceeded through the intersection. I couldn't have been doing more than 15 mph. I heard a loud bang and then the van started to make a loud noise. I put the van in neutral and coasted through the intersection. I had the van towed to butterfield Ford. They told me that the spark plug had blown out of the cylinder, plug coil broke in half, cracked the head. Ford would repair the van but would not offer me a warranty for the work done. So, I had the van towed to a local mechanic who repaired the van (refurbished engine) for $4,500 and they gave me a 100,000 mile warranty on the engine.