Help with P0306 misfire code on 2006 Jeep Wrangler 4.0

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TheDurtyJ

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2006 Jeep Wrangler X 4.0 6-speed

I have the dreaded misfire. The weird thing is it will occasionally go away and then come back. I can tell when it's going to come back because it gets noticeably rougher. I have tried changing out spark plugs, changed the ignition pack, new 4-hole Bosch fuel injectors, new oil filter, new air filter, cleaned the throttle body. I am at my Witts end with this and don't know what would be causing this. Especially when it occasionally goes away and runs perfectly fine. It did once throw the P0133 code, but that went away on its own and hasn't come back.
 
I had a similar condition and found it to be a small burn on an exhaust valve. My theory was that since the valve rotates in the guide very slowly it would only misfire once the bad spot on the valve aligned with the bad spot on the seat .. thus causing a loss of compression and a misfire. I was able to troubleshoot my misfire without spending any money on parts until I knew where the problem was. In fact I wrote a whole how-to guide on how I did it. You may want to look at it.

https://wranglertjforum.com/threads...the-dreaded-misfire-and-how-i-solved-it.4212/
 
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I will take a look at that guide. If you cleared the code would it be fine for a bit, and then come back after 25-100 miles or so?
 
CodaMan said:
I had a similar condition and found it to be a small burn on an exhaust valve. My theory was that since the valve rotates in the guide very slowly it would only misfire once the bad spot on the valve aligned with the bad spot on the seat .. thus causing a loss of compression and a misfire. I was able to troubleshoot my misfire without spending any money on parts until I knew where the problem was. In fact I wrote a whole how-to guide on how I did it. You may want to look at it.

https://wranglertjforum.com/threads...the-dreaded-misfire-and-how-i-solved-it.4212/
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I will take a look at that guide. If you cleared the code would it be fine for a bit, and then come back after 25-100 miles or so?
 
TheDurtyJ said:
Does this mean I need to get my engine rebuilt? / what kind of repair cost am I looking at?
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Not at all. In my case it was a head rebuild at about $350, but you are a long why from that decision. You need to troubleshoot it and find the problem. It could be an electrical issue, a compression issue, a fuel issue or a mechanical issue. Follow my steps and see what you come up with.
 
CodaMan said:
Not at all. In my case it was a head rebuild at about $350, but you are a long why from that decision. You need to troubleshoot it and find the problem. It could be an electrical issue, a compression issue, a fuel issue or a mechanical issue. Follow my steps and see what you come up with.
Click to expand...
Will do. Thanks.
 
I’m getting a p0306 code. I’ve got a 2005 rubicon 4.0. When I got the code I immediately took out the spark plugs and checked them and they all looked pretty good so I did a compression test and found that cylinder one had no compression and the rest were running between 160 and 170. I’m a little confused as to why cylinder one would have no compression and it would throw a code for cylinder 6
 
TheDurtyJ said:
2006 Jeep Wrangler X 4.0 6-speed

I have the dreaded misfire. The weird thing is it will occasionally go away and then come back. I can tell when it's going to come back because it gets noticeably rougher. I have tried changing out spark plugs, changed the ignition pack, new 4-hole Bosch fuel injectors, new oil filter, new air filter, cleaned the throttle body. I am at my Witts end with this and don't know what would be causing this. Especially when it occasionally goes away and runs perfectly fine. It did once throw the P0133 code, but that went away on its own and hasn't come back.
Click to expand...
Could be carbon build up on the valves. If you do a compression and its low on piston 6.
It's kind of pointing in that direction since you have eliminated the coil, spark and injectors being the problems.
Could all so be worn piston rings too. How many miles and have you had any problems recently? Like over heating? Ran engine on low oil? Blown head gasket? Engine running hot? Something going on in Piston 6. If compression is bad you might have broken valve spring too. That would lead to bad gas mileage and loud ticking noise in the engine. Carbon build up comes from cheap gas and higher mileage over 150k. Maybe give us a little bit more info about the engine mileage, history and maintenance.
 
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