BackFire/AfterFire.

[Spool]

I've know the two to be timing issues and fuel burning outside of the chamber.

Sometimes, on a cold start, I'll have a back fire from under the hood just before the truck rolls over.

But this morning, I go to start the truck and BANG! I've never heard my truck after fire like this before.
Grey smoke out the back, truck starts and my neighbors think a shotgun went off.

Any ideas to the sudden after fire?
 

[VileZambonie]

First thing to do is check for vacuum leaks and choke is working, then check your ignition timing. Make sure you don't have any wires crossed either, verify the firing order is correct.