I have a 2002 dodge durango 4.7 SXT 4x4. recently I changed the entire cooling system. I just replaced a blown head gasket as well on the driver side. After I changed the gasket I've had p0300, multiple cylinder misfire no matter what I do to fix it. I did a compression test and everything is at 200psi, which is perfect. I've verified that the fuel injectors all work. I've verified that ignition coils work, and have replaced two that had low resistance. I just fixed a an air leak from two of my fuel injectors on the bottom of them. I've replaced my oxygen sensors too. I've replaced all my spark plugs as well. I'm under 18 and don't smoke and dont have a smoke machine to find vacuum leaks in my intake system so I used the blower side of a shop vac and duct taped it to the throttle body. I turned it on so the whole intake system was pressurized and sprayed soapy water everywhere, thats how i found the air leak in the fuel injectors. but that was the only air leak i could find I've fixed it already. I've had this problem for a long time now and am really getting discouraged. Any advice or help is appreciated thank you.

 

What brand O2 sensors did you install? If you leave the front O2 sensors disconnected (after clearing all codes), do the misfire codes stay gone, and you just get the O2 sensor codes?

 

So i put in bosch O2 sensors from oreillys because I had the code p0030 for my o2 sensors, they were bad. I changed them out and now I don't have that code anymore. When i changed them i restarted my PCM so that it would recognize them. Before I restarted it I cleared all the trouble codes, and I havent had the code since i put them in (a couple days ago)

 

These trucks really don't care for the Bosch O2 sensors....... Won't necessarily set a code, but, the sensors don't give the readings the PCM actually needs to run the motor right. I have seen way too many weird driveability issues with the bosch O2 sensors. NTK, or Denso work MUCH better.

 

well it's too late to get that, i can't return it or anything. I believe they work totally fine right now. Just used a fancy scan tool and it said ignition system misfire. I'm going to look more into it. It's weird because I just changed all spark plugs, and two coil packs. maybe all the other coil packs have the right resistance but are iffy

 

Generally, if you have a bunch of the same part that live in the same environment, and one fails, you replace one. If two fail, you replace ALL of them.

Disconnect your front O2 sensor(s?), clear codes. Misfires gone??

 

haha, yeah but for me if one spark plug is bad then i replace them all so they all work the same. Didn't think about doing that with the coil packs. Right now im taking out my spark plugs and inspecting for ignition problems. My #8 cylinder spark plugs was fouled actually. from what looked like fuel. I used a borescope and made sure there was no liquid or anything sitting down in the cylinder, and there wasnt thank god. but there was only one fouled spark plug. maybe it was one spark plug and other coil packs thats causing the problem???

 

Entirely possible.