Here's one that ran pretty bad, 85 Chev 5.7 89k Miles. My intial thoughts after driving this rig (Class C motor home) was ignition trouble, and after getting the motor shroud off and hooking up my scope and getting the image below it was confirmed quickly. Cylinders 4, 5, and 6 were high on firing kv. Probably open wires right? Check my findings in the images below.

The first spike is the trigger point.

Typical burnt out wires. The bottom one is Cyl 1, it was on its was way out too.