1997 850 starts and stalls
 

please help with this! fuel pump kicks on and primes fuel system as designed for 1 second when first turn key on. 43 psi and maintains pressure. as soon as you start vehicle car will run until fuel pressure drops to low. fuel pump relay inputs ect all good except switch side from ecm when vehicle is running. if i bypass ecm and power up switch side of relay car will run all day. What makes ecm power up relay on key on prime, but not power up relay once engine started?