I had a 2003 focus PZEV, intake, exhaust... bla bla bla... at about 40k miles it spun a bearing... Ford gave me no issues on a replacement motor (it took about 4 weeks, because they wanted to send one of their inspectors out)... The tech told me that the engine looked like it had 3000 miles on it, I am anal on my oil changes. They have to prove it is the cause of the problem. I think this gets a bad rap with the older MAF Sensors getting gummed up by K&N filter oil from people who over oil the filters. To save face they say "$MANUFACTURER Voided my warranty because I put an aftermarket air filter on it and bla bla bla" When in reality they Dealer/Manufacturer said we can't cover this under warranty because your filter gummed up the MAF. Other like experiences would have only added to the fuel. Tunes, those are a horse of a different color. They can black list your VIN if you have or had a tune and it caused issues, that is if they spot it.