OK. I swapped out a 3.4L for an LS1 I didn't change BCM because I could bypass everything that i would need to bypass......... Fuel Pressure is steady at 44PSI. When starting you turn the key and you have to put your foot into it a little and then it revs right up good and healthy and strong but then after 5 seconds or shorter it just suddenly dies. I have checked spark and it sparks all the way up until the very end. I don't understand what could be the problem.... I bypassed the VATS I bypassed everything and their mom and don't know what else to do....... Please HELP!!!!!!!!

 

Maybe you shouldn't bypass everything. Maybe you should get an LS1 BCM. Just a thought. GM wiring is weird at best.