Coming from Phoenix here, I have a 07 Nitro RT, 4.0 Automatic with 226,777 miles, I am getting the P0304, I seafoamed it twice, ran fuel system cleaner twice over the past month, then I replaced all the coils with denso, replaced the recommended factory spark plugs, changed the oil, cleaned the manifold sensor, the intake air charge sensor, cylinder 4 injector replaced new, all the o rings on the other injectors, all four 02 sensors, air filter, checked all wiring harness to injectors and coils, replaced valve cover gaskets, replaced spark plug tube seals and still get a cylinder 4 misfire pending code, then after the emissions monitor and catalyst drive cycle its an active code for cylinder 4 misfire. The car sat for a year, so it had, p0456, P0455, P0300, P0301, P0304, I also changed the leak detection pump, the hoses, the purge valve solenoid. All codes went away except the misfire in cylinder 4 persists. No smoke, no overheat, not idling rough, no hesitation, just the misfire, motor barely shakes. As of now, I got all the emissions monitors to come on except evap, pending PO304 again. It runs great and I get 29mpg on highway. No other codes, only PO304. Don't have tools for compression test. I am assuming broken rocker arm or head gasket, but I wouldnt know unless I did compression /leak down test correct? Maybe crank sensor?