L4d2 or L4d Sky Walk Glitch

Name of glitch: l4d2 or l4d sky walk glitch
Gamertag: DBA MASTER 1

First clear cache,then play Left 4 Dead or Left 4 Dead 2 so on forward when it says update dont update.So next play the game put a pipe bomb or white fuel tank on ground some where in middle instead of edge then stand beside but a wee bit behind then shoot it when it blows up keep clicking.