I did a ly6 swap and I added a blower to a 08 rcsb..I went to crank it up and it wants to turn on for half a second but then it shuts off. I had a tuner program my ecm for the setup..any ideas what it could be? could there be something wrong with the tune?

 

do you have access to swap back to the stock tune? if so put the stock tune back in it and see if it will fire up and go from there

 

Is it the PCM that came from your truck originally. Was it reflashed to a different vin. Sounds like passlock if any of the above were changed and the theft deterrent relearn not performed.

Passlock will usually store a P1626 theft deterrent signal not received or incorrect if the passlock is your stumbling block but it sometimes wont store as well.

 

Could be a MAF problem as well.

 

+1, mind did this when I had my MAF installed backwards.