Ok, so I've got a 2008 E150, and I've got no compression on cylinders 2&4, so i pulled both of the heads, did a valve job along with replacing all the valve springs. Put it all back together and still no compression. So I pulled the motor and tore it down, the ring were bad, so i put all new rings in it, put it back together still no compression on 2&4, I thought the lifters might be locking up, so i replaced those as well, STILL NO COMPRESSION ON 2&4 , i don't know what to do now. If i pull the lifters out, so the valves are closed, and shoot air in the cylinders there are no leaks, and it holds compression, but as soon as i put the lifters back in it has no compression again, but like i said these are brand new lifters. I have run out of ideas and really need some help, also i replaced the EGR valve thinking maybe exhaust was some how getting into the head causing, and i replaced the PCV valve, but nothing works. It makes no sense to me what could be going on. Please help!