My 2006 Liberty has 111000 miles and has been very well maintained. 2 days ago engine began knocking. Checked all fluid levels and nothing was amiss. Nothing leaking. Anyway I pulled over when I heard the knocking and after about 15 minutes I tried to start engine. Would not start. After about 30 minutes it started and I limped home. No more issues until today. Was doing around 50 when I heard knocking again. Jeep began losing power and eventually stalled. I was unable to restart this time. The strange thing is that when I try to start the engine the serpentine belt engages turning the fan and the alternator, power steering pump etc. I can hear the starter turning but it doesn't seem to engage the flywheel. I changed the battery and starter about 2 months ago. My friends seem to think it's the timing chain but I'm not sure. I had a guy that's helped me before tell me it's the MAP sensor. Any ideas before I bite the bullet and bring this to a mechanic?