Upon diagnosis, cylinder #5 was misfiring. Checked compression on cylinder #5. Zippo. Something wrong with exhaust and/or intake valve. Lot of noise coming from timing chain area. Mechanic said fix would be easy $2K (new timing chain, cassette, new head, etc.) but recommends not doing it.. said it would just be a Band-Aid. Also seeing on this site people who've had repair similar to this one and then fails again in < 12 months. Recommended engine replacement (remember the existing engine has 135K miles on it). Used engine ~$3K but ones he is finding are all high mileage (e.g., 156K mi) and thinks that's a bad idea. Ford remanufactured engine would be ~$5K. But now I know this engine is genetically defective. While the vehicle is in otherwise excellent condition, these $ figures are beyond what it's worth (Edmund's TMV, Kelley BB, etc.). This thing is headed for the salvage yard. Replaced it with a used Toyota RAV4. I'm hugely disappointed in Ford after what I'm finding out about this engine and other Explorers. Someone should be shot. No more Fords.