For this hack to be undetected, use the following steps:
1. Click Play Now on Battlefield play4free
2. Open Punkbuster Blocker and select BFP4F.exe
3. Open Perx Injector and put it on manual and make sure its as BFP4F.exe
4. Select the hack4free V2.1 and click inject, it should work.
PS. make sure the Battlefield Play4free client is loaded to the lobby.