I have done everything! Cap and rotor, wires and plugs, valve cover gasket, fuel filter even changed the injector for the 3rd cylinder since that is the code that continues to drive me absolutely nuts. I am getting a P0303 and P1399 codes that will not stop haunting me. If anyone has any information i or ideas on what’s going on please help.

 

Did you verify valve clearance?
Did you verify the EGR manifold and runner ports were clear?

Both of these will contribute to misfire codes.

 

I would look into the short term fuel trim, the ECU is correcting a lean issue with 18.75% more fuel... vacuum leak maybe. A normal short & long term trim should be between -3% to +5%.

 

I don’t know allot but no one has said anything about a compression test yet ... if you have low compression it will make you misfire as well . They will loan you one at auto zone

also I thought I had a dead cylinder a while ago if you pull the plug and there’s any rpm drop the cylinder is not dead

 

Oh yea and you can check those fuel injectors as well get yourself a flat tip screwdriver put it on the injector and ear to the other side, if you hear a ticking there functioning
but I think .. I’m not shure .. they might be clogged even with the tick try some fuel treatment as well
👍👍👍👍👍👍
oh my bad I thought it was for a single cylinder
still check for oil in spark plug wells though