I have a 3.0 2004 Z4 with SMG...
More than 6 months ago the car would intermittently refuse to start. Turned over fine, battery, starter, et al are all OK.
Would tow to dealer upon which it would start
Recently it spent over a week at the dealer to no avail.
Then it happened again, at home, so I had it towed to a fairly local private BMW repair shop. Explained the entire situation, even suggested the SMG pump as I had read about what seemed to be similar issues with M3's. Mine had never stalled when it was running however.
The repair shop described the fuel system to me as a Fuel Pump Relay, The Fuel Pump Itself, and a computer module that controls the whole thing. At this time I was thoroughly frustrated and taking it back without changing anything would be insanity, so we changed the relay...
Two weeks later it failed to start again, while getting the emissions checked. Towed it back to repair shop and of course it started there. Kept it for a month and it started everyday... (it has 105k miles).
So then I authorized them to change the fuel pump. Upon getting it back I thought this might be it, as I had noticed that when the car did start it would stumble slightly before achieving a nice idle, and when I got it back this was gone. Hooray, or so I thought...
Two days later went on a trip to Virginia and it ran fine. On the way back we stopped at a rest stop and it would not start. Reset computer by disconnecting battery, no luck. This was on Christmas eve! Got a tow to a BMW dealer and upon taking it off of the flatbed, it started! We started towards home with only 2 hours till home. One hour in is stalled while driving in the left lane at 80 mph. Got towed the remaining 80 mile home and now my car is in my garage.
With a new relay switch and fuel pump, does this sound like the computer module? Have I been told a story? Has anyone experienced this before? Could it be the SMG pump?