I have a si manifold laying around and a dx motor that came out of my other car can i mate the two and put it in my hf with an si ecu.

 

Yes the si manifold will bolt to the dx head.

 

I s their any problems that come with doing that because I am thinking about doing a swap my dx for my hf. Because the hf gave me a code 8, put a new distributor on it reset the timing and cam and still won't start.

 

if it's already a hf, then it's already set-up for mpfi. if i read your last post right then you have a hf and you want to put in a dx motor with mpfi? if so then yea just put the si mani on the dx and have fun.