Saab: 1990 Saab 900 no start, crankshaft position sensor, fuel pump relay

Question
I have been working on my son's '90 900 turbo convertible and am making little to no progress. It just shut off on day and the running became very erratic after that. I discovered that the fuel pump relay wasn't pulling in. Even with jumpering it out, the car would only run poorly and stall if you hit the brakes. After trying to test all of the electrical components I could think of, I ended up replacing the ECU, the air mass meter and the APC. The fuel relay now comes on like it should, but the car will only start for a minute and then die. I am running out of ideas. Can you think of anything I should check? Thanks...  

Answer
The relay is kept energized by the rotation of the crank, once started, via a "retriggerable multivibrator circuit". This depends on impulses indicating rotation which originate in the
CRANKSHAFT POSITION SENSOR. Since you've changed most everything else, I would consider this...alas it is PRICEY!
 But before the big step, I would check all relevant wiring using a good info source such as <www.alldatadiy.com>, $25/year/vehicle, but positively worth it for a do-it-yourselfer!

           Hope this helps,

                      Jerry