Help!! Big problems!

[Niall]

My cars going in tomorrow for a full exhaust so I spent the weekend fitting a new manifold. Didn't go to plan but either way, the car is all back together minus a cat.

I needed to bleed the coolant as I had removed the heater matrix pipes to get the manifold in. I've placed the cat in place where it would sit but there's no fire ring in the cat so it's not sealed. I've started the car to try and bleed it and it's running between 3-4k. Please tell me this is because of a lack of back pressure through the exhaust?!?
Can't even bleed the coolant as the water pump is not sounding at all happy at them sort of RPMs. I've got it bled as best as by blowing through the over flow and covering the cap.
I did have the inlet off but I'm sure this is all back on where it should be!

Please help and tell me once the new exhaust is on it will run fine?! If not, what could be causing it?

Thanks and sorry for the essay!