I just install a JG header in my EF on Friday and then on Saturday I hit a bump on the ground and found my the bottom piece of my header got push in. All the screws were there on the header and no dents. The header sound like a open deck header and its feel like it lost power.

What could it be? And what can I do to solve this problem? Please help....

 

If it sounds like an open header, I can't see how there isn't a hole or a disconnection between the header and cat. I think you need to look at it a little closer. Could possibly be that you jarred a resonator loose, but I don't know if JG headers have them off hand.