Help. When I engage my rex engine , it starts and runs fine for about 30 secs. Then it gets louder and shuts off. Then it goes to ev mode. I ran a scan and get 300, 301,302 misfire codes. So, I assumed spark plugs since they have never been changed. I changed them and new coil packs while I had it apart. Didn't change anything. Got on one of those "fix it" websites and they said fuel pump relay. Changed that. Still no change. I'm at my witts end. Anyone got any ideas? Thank you