I put one coat of primer on it so far and I was wondering should I sand it before I put the 2nd coat of primer on? heres the pics





before pics(terrible)

 

if you want a good smooth finish you should spray and sand at least twice...but then again it is just a engine bay...
the reason behind spraying and sanding is so that you can fill up any imperfections that might be in the paint/metal....in a engine bay there really shouldnt be any bad scratches or dents or anything...
so really you shouldnt have to spray and sand, spray and sand...but if you want a extremely smooth engine bay then go right ahead for it.