[Gary Sullivan]

Are you sure you don't have air leaks at the connections or any cracks in the hoses? There is a great book on fuel injection which I have found really helpful. It is from the Metric Mechanic and is titled BMW Fuel Injection: An Enlightened Approach.
I find this an excellent source. It cautions against general replacing of parts and taking a methodical, approach to fuel injection which usually is more about adjustment of many f.i. parts rather than replacing them. I strongly recommend that book if you are doing your own work.
Good luck,
Gary Sullivan