I just recently switched to Castrol Syntec 10w-40 from the German Castrol I had in before. Vehicle is a fuel injected 383 stroker motor. I have never had starting trouble untill now (motor normally fires up very fast....and sounds mean) Motor will start fine for first two seconds ..... untill oil pressure rises, then it stumbles over for a couple seconds. Sometimes it will die completely. I'm at a loss and dont know what to do. I pu this oil in because it was a thin 40 weight (85.4 @ 40*C and 13.1 @ 100*C on a recent VOA) but had no idea it would act like this I should mention that my throttle body is modified for idle reasons to accomadate the more radical cam, but not sure if that would affect it that much.