Alright, I'm trying to see if my thinking is correct, or what you guys may think. Sorry for the long post, but I'm sort of talking myself through this as well if that makes any sense. I've got a 2007 JK two door (96k miles). I seem to almost always have a 0455 or 0456 code active (I'll deal with those at some point). A few months ago she started running rough and threw 0305 (misfire cyl 5). I figured it was time for plugs anyways, and it may fix the problem so I swapped them out. During that swap, one of the plug wires broke so I also decided to change out the wires. The misfire "seemed" to get better but was still there. I checked the codes after a few days, and only saw the two emission codes. The misfire has not been consistent. Sometimes it'll go a week with no noticeable issue, and then it'll do it everyday in the morning and after work for a full week. Usually when it has happened I'll stick my foot in it and give a few good revs and it subsides (doesn't go away but seems to minimize it). Last week before work, crank it up, it's missing about like always, give it a couple of revs and head down the street only to have the Check engine light start flashing. Turn around and check the code and also wanted to check the oil. Oil is good and all three codes are present. In less than a minute after turning around the light had stopped flashing (but was on) but the miss was hardly noticeable again. It's done that routine a couple of times since. This past weekend, i figured I'd go ahead and change the coil, and figured even if it ain't bad, I'l atleast have a new coil pack. Ofcourse the coil pack didn't fix the issue. It seemed to run much smoother for a couple of days but started right back up with everything after that. My plan right now is to check and make certain I'm getting good spark at that plug this weekend. If I have a a good spark, then it'll tell me it's fuel related and since it isn't affecting more than just the one cylinder, it's most likely no components leading up to the engine (fuel filter) and could most likely be that injector. Now for the twist...I do have an oil leak on that side, in the vacinity of the cyl 5. I'm not sure just yet, if it's the head gasket or valve cover gasket but this weekend I will also be cleaning that area off to get a better look. It's leaked for quite some time but has never reached the ground. It's just all gunked up in that area. There is also no pooling oil in the plug well. Yesterday I started thinking about a potential bigger issue and decided to check the oil and smell of the dipstick. There was a pretty strong fuel smell in the oil. So now I'm thinking I need to do a compression test and see if maybe fuel is getting by the rings and that's my problem all together. So...I'm hoping this is not a ring issue and trying to figure out if all these symptoms could be explained by an issue other than ring failure. Is there another way for fuel to get into the oil? Would there also be a visible distinction of fuel in the oil? The oil looked fine to me. The valve cover wouldn't cause a misfire right? Unless it was filling up the plug well I think (which it is not). A blown head gasket, could cause the misfire, but that wouldn't allow fuel to enter the oil I don't believe. I guess if that injector is leaking it could slowly fill up the cylinder (and maybe allow fuel to seep past the rings and into the oil), but wouldn't that be hard to start? And if that were the case, wouldn't it run fine once I got out on the road and not have all the hesitation and jumping as it missed? Just looking for some other thoughts on all this. I don't have the compression tester just yet, was planning to order it this week.

Oh, and if fuel is getting by the rings and into the oil, would that cause the misfire, and if so, would that be a consistent misfire and not as sporadic?

 

Maybe check your fuel injectors. One or a few of them could be failing and giving you these issues like fuel getting into your oil. According to this site: https://dannysengineportal.com/fuel-...of-three-ways/

Possible Signs Of Fuel Injector Issues Include;

• Hard Starting when engine is hot
• Poor idle
• Failed emissions test
• Poor Performance
• Engine does not reach full RPM
• Increased fuel consumption
• Rough engine performance
• Surging and bucking under various throttle loads
• Smoke from the tailpipe
• Oil thinning, which can lead to catastrophic engine failure
• Engine Knock or Detonation which can lead to catastrophic engine failure
• Pollution

 

I think I'll test the compression to rule out a bigger issue, and if that's good, I'll deal with the injector. I know I've had to replace a couple of O2 sensors in the past and found out to ALWAYS get the O2 sensors from the dealership. Do injectors fall into this category as well, or is an after market injector just fine?

 

Sounds like a good plan. If you need injectors, I would go factory unless someone else chimes in with a good aftermarket brand. If you have time to wait, I'm sure you know to avoid the dealership and save money buying Mopar injectors (4861667AA) online....or anything else for that matter.

 

Confused more now. Checked spark just to rul out ignition (it was good) then started to remove plugs to start compression test and saw this on my number 5 plug. Part of the electrode insulation is missing. Now I'm wondering this would cause a misfire. Although I had the misfire prior to installing this plug (it was unbroken when installed).

 

Looking at that sparkplug, couple things come to mind....defective sparkplug that was already cracked (unlikely), wrong heat range spec'd sparkplug(?), or a lean condition causing detonation that has been developing with cylinder #5 since before the recent spark plug change. First, you should see if you can blow shop air into the #5 bore to blow out that porcelain piece if it's still in there. If you have a borescope (cheap ones connecting to phones can be found online), take a look-see too to make sure if possible. Check your compression as you planned to rule it out since it may be a contributing factor through carbon buildup atop pistons.

Using THIS GUIDE and relating it to our JKs on causes for detonation:
1. If you borescope the cylinder, check for major carbon buildup compared to the other cylinders since it can cause it. If #5 is heavily carboned, then your piston rings theory could be validated with oil carbon buildup from a stuck oil ring letting oil creep up to the top of the piston.
2. EGR not working as efficiently can also cause it since this will make the cylinders run hotter...but not likely just one specific cylinder.
3. Incorrect spark plug heat range can run too hot, but it would have been occurring in multiple cylinders since the plugs are all the same.
4. Lean condition caused by a vacuum leak or a faulty injector to a specific cylinder.
5. Faulty knock sensor, but it would be an overall problem and not just one cylinder. (inexpensive & easy to change if needed).
6. Engine overheating, but this wasn't an issue here to a specific cylinder.

The only two I see possible in your case are #1 and #4 since it has been cylinder specific all this time.

EDIT: I just thought of this....EGR is attached adjacent to Cylinder #5 in the back. So, not ruling this out completely.

 

I'll take a look in that cylinder and see if it's in there and check the piston. I'm hoping it got blown out of the exhaust valve. If this all happened because of a lean condition causing detonation, then wouldn't that still be happening? Are there codes that pop up with a lean condition as well? I've not seen any so I'm not sure if any even exist. Thanks for your input on all this. It's much appreciated.

 

That was my bad for conflating the misfires + blinking engine light with possible detonation. If it wasn't detonation, then I wouldn't know how to explain the chipped sparkplug ceramic unless it was cracked somehow on the way in. I recall someone here having misfires and going in circles until it was ultimately found to be a simple break / cut in the plug wire that was leaking out spark. Incomplete combustion in this case could explain the gas getting into your oil too.
This spark leak is probably easy to diagnose in the dark while the engine is running. If you're still getting a specific #5 misfire, then as a test use one of old long plug wire you took out earlier to see if it improves.

 

It is possible it was broke during install and you saw no difference. Did you do the compression check? I am thinking back to the smell of fuel in the oil.

 

Haven't done the compression check yet. There was definitely no throwing the plug around or dropping it or anything. It's run very smooth all week since I replaced that plug.