About a month ago my parents asked me to help out with changing out the head on their 1997 Blazer (V-6). Once we got to the valves we had my expert mechanic uncle "adjust" them, he did this with the truck running and by sound. After doing so my parents took the car on the way to the grocery store, needless to say they never made it. My cousins, his sons, told us that the original mechanic who told us the head were fine and didn't need to be plained was wrong (even though he said he had tested them thoroughly). So we set out to take it all back apart to have them plained, once we got to the valves again we found that they were all loose, in fact some of the push rods weren't touching anything. Despite this we took it all apart and had the heads machined. Now we have it all back together and I have set the valve lash in accordance to my chilton's manual that says that they should all just be set to 20ft/lbs. The problem is it doesn't start at all, it seems like it is about to start then there is a psht sound and a few sparks that shoot out of the intake. I have no idea what to do, any help would be more than appreciated. Thank you so much for you time.

 

sounds to me that you might have got a plug wire crossed, or the timing is off, have a read thru this thread https://blazerforum.com/forum/tech-articles-diy-29/edi-engine-timing-24373/.. hope this helps