3.8 V6 LX, It will start and run for a while and runs good while running, but some times it shuts off, and will not crank unless you put a charger with 300 cranking amps to the battery. It will fire with starting fluid but just wont stay running wiyhout the booster box. ive replaced the fuel pump, the fuel filter, the disributor cap and rotor button and battery. and the proplem is still ongoing. and also im getting fuel to the fuel rail i check the valve stem on the rail and it spits fuel. Any hel would be greatly appreciated. Thanks.

 

Have you considered checking the battery cables?