Hello Scotty , I have a Jeep Liberty 2010 that I bought used with 112000 miles on it, long story short I got it from a used car dealer , the check engine light starting lighting up with P0305 coming on and off since first week.dealer has tried to fix it about 15 different times now they sent it to jeep and they said the cylinder head for number 5 was damaged they got a different mechanic to change it but 2 weeks later check engine light came on and off with now P0306 code it’s been four months since I got it and still no real fix .any idea of what could it be ?
change numeber 6 spark plug if the dose not help do a comperson test on that cylendor
They changed all the spark plugs, coils ,plug wires , and did a compression test also and fuel system cleanse
it could be a lot of things. A bit hard to diagnose over the internet, and ultimately the dealer is responsible for finishing the job ... even if it means replacing the car.
You need deeper diagnosis - even after replacing all those ignition parts the error codes still come up. Well, we can now assume that the parts you put in are not the fault and didn't change a thing. You have to keep on looking. Missfires can be usually too lean of a mixture and thru the scanners missfire monitor you can see the missfire in real time. You have two cyl next to eachother which can indicate they suffer from a one source air leak - thus leaning out your cylinders. Another scenario is that the two injectors are at fault although thats iffy at best. If compression on #5 and #6 are as even as the rest..your engine is fine mechanically speaking. So the hunt continues...Is their a PCV valve near those bad cyls ? or any vacuum tubes ? Spray some Brake Kleen near the intake on those cyl to see if the rpm goes up as a vacuum leak makes the RPM go up if their is a leak. Check your clamps on any intake ducting..make sure they are tight...any air that gets in thru them is not metered and causes imbalance. Other ideas are EGR valve leak or stuck partial open.
