So one year ago, I was running the car hard on the autobahn for almost an hour straight. Was running good, running fast. Maybe I pushed it a little too hard for too long (or maybe not!).
Suddenly it ran like absolute ass so I limped it to where I was going and left it parked there until I could figure out what was up. Pulled an injector code on cyl #2. Ok, so I'll just replace it. Limped it back to my own home, tore into it, replaced the injector and fired it up. Still ran like shit.
Ran comp test, cyl #2 was way low. So I let the car be and didn't drive it for the longest. Finally got the extra time to tow it to the hobby shop I always use and tore it down. And there it is, the year-long mystery solved.
Cyl#2 fuel injector gave up, leaned out the cylinder, and one of cylinder #2's exhaust valves paid the price.
My buddy just went through a similar situation with his F150. He was racing an Audi and lost compression in one cylinder under similar circumstances. We suggested he may have suffered ring land failure. He bore scopes it, finds a busted valve and brushed off the concerns about the piston.
Rebuilds the heads, puts it back together, switches from a 3.75” pulley to a 3” pulley and proceeds to put a rod through the intake valley.