I have been going through my Haynes manual all night.

 

The only thing I can think of is that the timing chain got screwed up some how and that is why its back firing like it is. Because the valves are open when it fires.

 

That's about the only reason you would get a backfire... plug firing while valves are open.

Under normal circumstances, I would have a look for failing components... or, if the engine needs to be synced, for crank position, or some such. Your case isn't normal though..... I would check and verify that the wires that actually fire the coils are both originating from, and terminating at, the correct points. Are you coil near plug? (eight coils) or do you have coil packs servicing two cylinders each?

 

i forget what you have said you exactly did to your engine but did you do a compression check on the engine? maybe there is a bad valve. a guy doing a hemi swap into a 81 dodge posted some pics of the damage he found in the hemi he was planning on using.http://bit.ly/HbGubG

 

There are a few things that make motors back fire out of the carb.
(1) Is Timing .. "Chain" , or tension , too loose..
(2) Is an air leak in the intake manifold..There are 2 hoses on the driver side behind the throttle body . make sure there both hooked up..check for throttle body gasket leaks. etc..
(3) is valve seats.. There's an intake valve not seating and it's allowing ignited fuel to come back through the carb..
If you didn't mess with the valves , this probably is not the problem..
(4) Could be the spark plug wires.. Make sure you don't have any crossed..
(5) Wiring..This is a long shot , but if you don't have a wire hooked up somethings not working..Check all you're grounds and connections..

ALSO , after you changed the sensor , did you reset the computer.. I went to Florida last week . On my way home , my Ram started running like CRAP..It wouldn't Idle right , and taking off from stop without it stalling was impossible..I pulled over in a parking lot and started tracking the problem.. Turns out one of my 02~sensor wires grounded out on the [pipe and melted grounding it out.. After fixing the problem , It still didn't run right until I re set the computer , Then it went back to running like new again..

 

If you can't find the problem with that list , I don't know what else to suggest . I have racked my brain and read this whole Haynes manual and spent hours searching the computer for posts that might help.. If we could get together somehow , I could help , but without seeing it and being able to put my hands on it , I don't know what to do..
Keep us posted ...

 

the hemi has 16 spark plugs two per cylinder 1 coil pack per cylinder each coil pack fires the cylinder below it as well as the cylinder adjacent to it up when I took the manifold off I made sure that each spark plug wire was going to the correct spark plug as well as the correct cylinder I'm thinkin that the timing chain maybe out of tension because when I redid my valve springs all thr valves seem to be seeing how they were supposed to be I'm not sure if there's a vacuum leak I'll have to check that that's news to me I know the throttle body is isn't leaking because I replaced the gasket on it when I took it off in cleaned it I'm thinking I might have to pull the motor out and pull the heads of to find out what exactly is going on.

I did reset the computer as well before I tried to start a truck it just continues to backfire out the throttle body which makes me think it's gotta be a timing issue nothing else would cause it other than maybe a bad valve but then it would be every time the engine cycles through it would backfire where as this is more of an intermittent kind of backfire it doesn't happen every time.

 

Sticking valve??

 

I cut my plug wires short and put the "plug side" ends back on..They come from the coil then to the same cylinders second plug..BUT from the factory Each cylinder has a companion cylinder I think "Maybe" ~ you have them wrong it's not the cylinder below or adjacent to them..this is the order they should be in .

1 coil to 6 plug - 2 coil to 3 plug - 3 coil to 2 plug - 4 coil to 7 plug -
5 coil to 8 plug - 6 coil to 1 plug - 7 coil to 4 plug - 8 coil to 5 plug..
The cylinders that are companions are 1/6 ~ 3/2 ~ 4/7 and 8/5..

It's just an Idea , sometimes the hardest problems have the simplest solutions ..
I'm sure you've probably checked all of this , but I'd start all over and make sure everything is right before pulling the motor ..

 

I don't know man , I've just looked through all you're pics.. I can't really tell , but It looks to me like you've probably got the plug wires right..
It's a complicated thing .. I'm gonna hate seeing you pull that motor back out..I'd still check all the wires first.. I wish I were there to help..