I remember this issue being discussed last winter but my memory fails me. My 2000 4.3 blazer is always an excellent starter until the temp. drops to about 20 deg. At that point, it gets progresivly harder to start as temp. drops. You crank and crank and finaly fires but dies right away. After doing this 20-30 it sometimes starts. If I pour gas down throttle body, it fires and runs till that fuel is burnt off. Even with a 250 amp boost, she still behaves the same.(except for spinnin at bout 3 times normal crank speed)
I have not checked fuel pres. but would think with that much juice in system, the pump should be recieving plenty of power.(OR NOT?) HELP-Winter's comin!!

 

First I would check the fuel pressure, it should be 60psi. Next I would check the coolant temp sensor.