So here are the details, I have a 2002 Mustang with a 4.6, the number one cylinder blew the spark plug out before I purchased it. The previous owner had a heli coil put in to fix it. Recently it started missing on that cylinder, when I pulled the plug out the heli coil came out with it. I replaced it and put the heli coil back in. The cylinder then started to leak out around the plug. When I tried to pull the plug out it was sunken down to deep in the head and I couldn’t get the spark plug socket to get a bite on it. Yesterday it blew the plug out again, only this time I put a new heli coil in the correct way and a new plug (the old one had ran in the piston) when I started it it seemed to be missing but there was the sound of air escaping (like a vacuum Leak) upon further inspection I found the number one intake runner was extremely hot like exhaust was escaping up it in to the intake. The only thing I can think would cause this is if the valve was bent or not seating correctly and causing the exhaust to escape in to the intake runner. Is it possible for the valve to hit the spark plug? Any ideas would be great before I tear in to it..