Is the car turbo or non turbo/ what kind of car? I would suggest making a leak tester. and pressurizing the motor, you will find the leak trust me.
http://www.youtube.com/watch?v=atretf9u-Mc
That should give you an idea how to make one. I just use some silcone coupler that fits whatever im clamping it too, and drill a hole in a pvc cap and pull a tire valve stem though, make sure the holes small so the valve stem fits real tight.