After installing the NGK TR55's, I get misfires when at idle, and when flooring it, there is major backfire popping noises....like fireworks...I immediately got off the gas. I've checked all the plugs and wires, they are all hooked up and snapped in twice.

I did leave two stockers on cyclinder's 6 and 8, because I had trouble getting them out. I will switch them soon, but that shouldn't be the problem, right?

Please help, thanks!

 

no way to know unless you take em out. I assume is didn't do this before? how do the wires look? are they gapped properly?

 

No, it didnt do this before...the wires look good. I didnt know the plugs need to be gapped?

 

i would think that if everything was fine before the install, one of the plugs isnt firing then going on burning off the unburnt gas causing a pop....definately a bad plug or loose connection.

 

Gap them at .050. Get the #8 from under the car, it is a snap that way.

 

yea, I jacked the car up and everything...but I need an 1'' extension, because the 3'' was making my hand hit the damn heat shield.

 

Usually the TR55's will be gapped at .059" -(good enough) although the last set I installed had a little variance.
If there was any crud in the plug recesses in the head you may have got some crud in the plug gap while wallering around in there trying to hit the hole.(though usually not a problem)
You may have accidentally closed the gap on a plug while installing.(I've done it before on hard to reach plugs)
But worst of all, you didn't finish! you have two plugs left, LOL.
Seriously, though, I have a high mileage engine with no major oil leaks, but dirt and crud will find its way onto the heads. I try to rinse mine down at somepoint B/F plug install.
Worst case, r&r the plugs, inspect each one.