My buddy tore the top part of the engine down to freshen it up, but after we got it all back together, it will not fire/start. It will turn over fine, but there is not firing. The distributor and all of the spark plugs are fine. The fuel pump is coming on. He did take the fuel rails off, so could that be the problem? I saw that the MAP sensor wasn't plugged in and thought I had found it, but it still won't start. We need help.