So my car has recently had a new motor put in it, was running fine the other week for about a week and then started having issues staying running and while I was driving it one night I suddenly couldn't accelerate more than 5mph without pumping the gas to keep it running long enough to get it to a safe spot to park and check it out, only get a P0300 code and I already replaced all the spark plugs, tested each individual injector all work fine, have fuel pressure, new coil packs, new fuel filter, but it will only crank crank crank and most times will fire but not always fully start running and when it does it only runs for about 2-5 seconds before dying again, I have no idea what else to check at this point and need any tips or pointers on where to go from here please. Thank you. ~Josh Jeffrey Brown~

 

A bit of a long shot without more detailed diagnostics:
-first Id unplug the MAF and try to start it. May have suddenly got a vac leak thats skewing fueling way off. Could also be checked by O2 readings / stfts
-second Id check the icm. Given the age, I see it come up more and more as a failure point.

Also, just to be sure, is it holding fuel pressure 100% all the way up through when it dies? Ive seen fuel pumps spike pressure ok engine off (when its easy to pump, doesn't actually have to supply anything), but once running they roll off fuel flow as they can't keep up.

 

I'm now getting these codes on the obdII P0449 Evaporative Emissions (Evap) vent solenoid control circuit, P0300 multiple engine misfires, P1626 Theft deterrent fuel enable signal lost, U1064 lost communication with body multiple control (BCM) system, any ideas why these codes are showing up and how I could fix my car to not have these misfires anymore?