P306 Error code on 2016 JK

M

msgntsu

New Member
Joined
Oct 10, 2022
Messages
15
Location
MD
I’ve tried to research as much as possible, but really didn’t find anything to help me diagnose my error code. I woke up this morning to an engine idling a little rough (by the way, i didn’t notice the rough idle after driving somewhere - only at cold start) and then my check engine light came on. Checked code to find it was a P306. I researched a little to understand that it was a misfire on cylinder 6. Seems to be a wide range of possible issues, but way too many to just start diving into. The jeep has 98K miles. I changed plugs at 92K (Along with oil cooler filter housing). Based on that it seem unlikely that it would be a bad plug, but I guess that might be an incorrect thought. What is the best way to start trying to locate issue? As most know, it’s not simple to just pull plug on that side. This is also my daily driver, so I need to resolve soon.

Also, are there risks with driving it with that code?

Thx.
 
Clear all codes. Swap your coil pack and plug wire to another cylinder. See if the misfire travels with it.

There is no risk to driving with any code. There is, however, a risk to driving with a misfire. Uncorrected, it can damage or destroy your engine. It is probably not going to happen instantly, but there are a lot of variables and no way to know for sure.
 
  • Like
Reactions: Duster
Thx Dirty Dog. After a little research, it appears that #6 is on the drivers side in the back. I had originally thought that it was on passenger side. Correct me if I am wrong. What you say makes a lot of sense and was something I thought about. Was just hoping there was an easier way before doing that much work. I can swap, but a few questions:

(1). How do I do the swap above without driving it some number of miles? Just concerned as you state above about driving many miles with a misfire.
(2). Unless my memory is mistaken, I pulled the upper intake manifold to get to plug. If that’s correct, do I have to replace the gaskets again. They are about 6 months old and have about 6k miles since my oil cooler swap

Thx. again for the help.
 
You don't need to go on a road trip after the swap. Just fire it up. The CEL should come on again pretty quickly, and at that point it's just a matter of scanning the codes. If the code has moved to the new cylinder, you know the problem is the wire and/or coil pack.

You should be able to get to the wires without removing the intake. You might need some plug pliers.
 
Thx. again. I just went and looked. If I have it right and it’s the back plug on the drivers side, then I do need to pull the upper intake. The passengers side would have been much easier. Just my luck. Please advise if I have the wrong plug. Also, let me know what you think about reusing gaskets on upper intake.
 
Hello, I thought I posted an update last night, but I guess I did something wrong. I replaced the ignition coil, but that didn’t work. I decided to just drop it off at the dealer yesterday. They did all the initial checks. They are not asking for more diagnostic time to remove valve cover and check litter. Hmm. Wouldn’t I have heard a ticking noise if the lifter was the issue?

Thx again for the help.
 
msgntsu said:
I’ve tried to research as much as possible, but really didn’t find anything to help me diagnose my error code. I woke up this morning to an engine idling a little rough (by the way, i didn’t notice the rough idle after driving somewhere - only at cold start) and then my check engine light came on. Checked code to find it was a P306. I researched a little to understand that it was a misfire on cylinder 6. Seems to be a wide range of possible issues, but way too many to just start diving into. The jeep has 98K miles. I changed plugs at 92K (Along with oil cooler filter housing). Based on that it seem unlikely that it would be a bad plug, but I guess that might be an incorrect thought. What is the best way to start trying to locate issue? As most know, it’s not simple to just pull plug on that side. This is also my daily driver, so I need to resolve soon.

Also, are there risks with driving it with that code?

Thx.
Click to expand...
It sounds, from what you say, as if the rough idle goes away after it warms up. That could mean the spark is weak for some reason. I would suggest first clearing the code. Then starting the engine from a cold state. Wait for the rough idle, or check engine light to come back. Immediately stop the engine. My personal first step would be to pull the plug and check its state; wet with fuel, showing carbon, etc. If it is, check the gap first. There is a possibility you changed the gap accidentally while changing the plugs. If the plug is OK, then you move on to the coil and wire. Swap them with a neighbor cylinder, start the engine and see if the rough idle is still there, and if the CEL comes back. If the CEL shows, does the code move to the cylinder you moved the wire and coil to. If it does, you have your solution. If it doesn't, I would head for a mechanic who knows his stuff.
 
Grrr…. I got a call from the dealer late this afternoon. After Senior tech review and consult with another senior member, they believe my jeep has a slightly burnt valve. It did pass compression test, but they have seen them pass before and still be have burnt valve. Now, I am faced with investing more (a lot ) money and still no confirmation that this is the issue. They are supposed to call me on Monday with the est. to fix if it is a burnt valve. He did say 6 more hours (on top of the two I have already approved)…. So frustrated…. Again, 98K miles.

Comments…
 
Update…. Dealer just gave me a quote of ~4K to replace drivers head with reman head. Also pulling passenger head to confirm no issues. This is a risk avoidance since it’s just 2 extra hours of labor. This is beyond frustrating.

Is this a good investment in my jeep? I know it would be more, but should I be looking at a replacement engine??

Thx for the help.
 
msgntsu said:
Update…. Dealer just gave me a quote of ~4K to replace drivers head with reman head. Also pulling passenger head to confirm no issues. This is a risk avoidance since it’s just 2 extra hours of labor. This is beyond frustrating.

Is this a good investment in my jeep? I know it would be more, but should I be looking at a replacement engine??

Thx for the help.
Click to expand...
What kind of break will they give you if there is no burned valve? A question worth asking.
 
Thx for the reply. They said they ran a bore sight down the hold and can see it doesn’t look right. The service manager said he is 100% sure the problem is in the head. Still pissed that I have any kind of engine issue at 98K. Called Chrysler today to complain and ask for help. Waiting on their return call…
 
msgntsu said:
Update…. Dealer just gave me a quote of ~4K to replace drivers head with reman head. Also pulling passenger head to confirm no issues. This is a risk avoidance since it’s just 2 extra hours of labor. This is beyond frustrating.

Is this a good investment in my jeep? I know it would be more, but should I be looking at a replacement engine??

Thx for the help.
Click to expand...
I am not sure all the cost, but isn’t a Jasper engine around 6K? Of course then there is cost to install etc, but it’s the entire engine and warranty. From what I’ve heard they have fixed a lot if the ”flaws” in the stock engine.
 
Top Bottom