Backstory: Three weeks ago, after a weird loud banging sound, the Jeep ran horribly. I read the codes off of the odometer and got P0320, P0352 and P1391. Not really knowing where to start I decided to check out the oil pump drive that I'd replaced with a used one last year (it was used because I couldn't find a new one, the parts stores and dealerships both said backordered). The last time the magnet in the sensor came loose and fell, mangling the pulse ring.
Not the case this time, but I did notice that my oil was thick like gravy. So I drained it and replaced the oil pump, the oil pump drive with a brand new one, plus plugs (Champions) and the ignition coil.
For a while I was getting P0300 P0303 and P0304, but now I'm down to just getting 0304. I pulled the electrical connector from each injector one at a time, and the only one that didn't make a difference in the way the jeep was running was #4. I pulled the spark plug, it looked like it may have fired a few times, but not a lot of indication of it. Hadn't fired recently though, because it was damp with gasoline.
I saw one of Jeepguys answers from a couple of years ago that talked about #3 injector being too close to the exhaust manifold and heatsoak causing a misfire. Is this possible on #4 also? Is there something else I should be looking @?