525 i bmw 1990 250,000 miles

i have this bmw that wont start up. i changed spark plugs, the alternator, starter is good, distrubuter cap, and the roter for the distributer. and nothing has changed. it still putt putts and no ignition.

p.s. and i changed the presure gas valve. it sits right next to the intake manifold with a gas line hooked up to the back side and another line hooked up to the front going in to the intake manifold.

please help thanks guys. :D