I have been struggling to fix a reoccurring misfire on cylinder 7 of my 2005 Dakota. I have the 4.7L HO if that makes a difference.

I am getting a very rough idle and its throwing P0307. I have replaced the spark plug and I swapped out the coil with one from another cylinder to see if it followed but it didn't.

I checked the compression on all the cylinders and they were all within range and within deviation.

What would be my next logical step? Fuel?

Thanks everyone.

 

since it stayed on cylinder 7 when moving the coil, then it's, hopefully, either the plug, or the fuel injector. If not then you may have a valve issue, a cam issue, a piston issue, etc...

Check the plug first as you already know that the coil is good. Swap it to another cylinder and see what happens then. If it stays again on cylinder 7, swap a fuel injector. It could also be a fault in the wiring harness. If after all this and you still can't find it, then i would bring it to a mechanic to check the engine internals.

 

This may go without saying but make sure you clear the code after you make any changes to ensure it's not a hangover code from before the change.

 

I would guess you have a plug issue, injector issue or something with the harness. Especially since you did a compression check which rules out the valves and or the piston. Erase the code and see if it comes back, if so swap the injectors around and or put some new plugs in it. If that doesn't work, start hunting for a broken wire. I had a car once that had cracked porcelain on one of the new plugs that wasn't visible. I ruled everything out that I could and finally took it to a dealer for diagnostics. After they diagnosed it, I changed out the new plugs with newer plugs and all was well.

 

also keep in mind that the 05 trucks had issues with the cylinder heads.... that would cause rough idle and can also cause a misfire. i know you have done the compression check,

here is a list of things I'd try before ruling in the mindset of the head,: double check the spark plug, try moving the plug to another cylinder as well. if its still there try moving the injector, if you have done that then start checking wiring for the coil and injector. if everything else there has been watched... check your timing...and last but not least the head itself.

 

Swap 2 injectors. It's not hard. You need some Vaseline or something to put them back in so you don't roll the O-rings. Release the fuel pressure first.


Does it miss worse for a few seconds when you start it after it sits a while?