The owner buys vehicles at auctions and this is one of them. He checked the oil in it one day and thought it was low, poured 5 quarts of oil in it and it slung a rod through the block. He later discovered the dipstick was cut and be way over filled it. After that tidbit that could be useful, so he brought it to me to change the engine out and he bought an engine from lkq and it turned out to have a bad bottom end so he warrantied the engine out for one that we heard run. I dropped the second engine in and it ran but I got a p0300, p0302 and p0306 and it idles like crap but smooths out around 2400 rpm. Upon first start up it blew chunks of the drivers side catalytic converter out the exhaust. Cylinder 2 and 6 plugs are wet (gas) when I pull them, they are both getting spark, obviously getting fuel and I'm stumped. I sprayed starting fluid all around and can't find a vacuum leak in the new intake gaskets. If the coil packs are unplugged on those cylinders the idle doesn't change, I haven't tried unpluging the injectors yet since they aren't accessible under the new gaskets. Compression is a hair under 180psi on the 2 cylinders, I've cleaned the throttle body, replaced it with a known working one that is fine on another 3.6, swapped out coil packs even though there's spark, cleaned sensors, cleaned the oil out of the intakes, swapped out injectors, used an ecm that I ended up having to jump the starter relay due to a "starting disabled remove key" message and it idled the same. I've cleaned all grounds very good, battery is good, I put new oil/filter in it but read oil changes have cured this so I tried that, new properly gapped plugs, picked through wires for quite a while and I'm at a loss. I've been doing a lot of searching and all of the post die or their success stories don't work for me. Will that junk cat cause this? I've pulled the exhaust off right behind the cats and it's hollow. Sorry for the whole book but I'm just trying to give all of the details. I figured I would get some kind of bad converter code but nothing other than the misfire codes show.