do these things just go bad all of a sudden?

i replaced #2 in august when it simply fell off the engine.
i am replacing #6 today after the engine light went on.

both times i was under a load and lost both loads.

is there a way to scan the packs to know if they are on their way out?

i just called my local goodyear dealer. he told me to replace the remaining 6 coilpacks and install is about 700 dollars. so why does ford get 700 dollars for 1?

btw this is at 260k. the first was replaced at 230k i think.

 

You are lucky they usually start failing long before 230K miles. I lost my first one around 190K and replaced all 8 with my last plug change. Go to ebay and buy a set of 8 for around $100, and yes they do go bad. You can also measure the resistance to see if they are getting weak but I don't know those numbers off the top of my head.