boatgeek

hi folks,

Sorry if you guys think this is an obvious issue, but I'm looking for help with a noise that I'm guessing is spark knock or engine ping on my 2012 JKU (3.6 pentastar, w/ manual). It started at about 3000 miles, and as gotten worse over time (I now have 14000). It seems to exist between about 1700 and 2100 RPM or so, and I find it in 3,4,5,6 gears. It improves somewhat when I use high-octane fuel (which is why I think it is spark knock), but by no means goes away, and it is irritating to have to use the expense gas. It only happens when the vehicle is warm (so ironically my favorite time driving the jeep is when it hasn't warmed up). And it seems a worse in hot weather. It was really bad when driving in the summer with my small (<1000 lb) trailer full of camping gear, especially on modest grades, though this was before I started using premium. When its bad its really bad, like makes you grimace and is not fun for driver or passenger -- makes me want to get rid of the jeep (which I otherwise love and focus much of my attention on).

The dealership says I just need to use premium, and that's as far as I've got with them. Will try going back, but I don't want to be told that it is par of a JK.

Anyone else had this problem?

I'm perplexed as to how a brand new engine in this day and age can have this problem. The last time I had this was on an 84 Land Cruiser FJ60 (with a carburetor!).

I've heard it said that this is due to carbon deposits... can someone educate me as to how this works? I thought it was somehow due to the fact that the spark fires before the optimal time in the piston stroke, i.e. a timing problem. Seems like it could be fixed electronically... (Thanks for the education). I've also heard that it can be improved with the combustion chamber cleaner, but this also doesn't make sense to me.

Thanks in advance!

Ryan0260

It sounds like you are dealing with carbon buildup. It can be caused by anything from cheap fuel to driving habits, and many winter blend fuel mixtures make it worse. I have found a good way to help this, as I have dealt with it myself. 1) get a bottle of seafoam at an auto parts store, and put in in a full gas tank. 2) go to the dealership and grab a bottle of Chrysler combustion chamber cleaner. Follow the directions. It is sprayed directly into the throttle body, then you shut off the engine for several hours if possible. When finished, take it for a good hard drive to blow everything out. It wouldn't be a bad time to change the oil either. Try this and tell us how it does. If buildup is bad, it may require two treatments.

efan450

Spark knock is a nickname for pre ignition (detenation). Its called pre ignition because the gas in the cylinder is being ignited before the spark plug fires it like it was designed. Pre ignition can come from many things, improper replacement parts, too low of fuel octane, an air leak, carbon build up, ignition being Set to far in advance, etc. carbon build up is a result of unburned fuel and exhaust that builds up inside your cylinder head and as the motor warms up these little deposits start to glow red hot and actually ignite the fuel before the spark plug gets a chance to. That is pre ignition, the octane (for lack of a better explanation )of your fuel is the amount of heat energy it takes for the mixture to be ignited...the higher the octane the hotter the spark needed to ignite it, therefore higher octane will help if its caused by carbon build up...the fuel will resist being lit by the glowing carbon deposits and doesn't light until the spark plug fires. Your owners manual should say 87 is fine, so requiring higher octane is masking some other issue. Have you researched pentastar head/ticking problems? They start with a tick much like you describe.

boatgeek

Thanks guys. The notion of the carbon deposits glowing hot helps.

So is this indicative of piston rings not sealing well, or some other fundamental engine problem? Would / could synthetic oil or a different weight of oil help?

I did look a bit at the head issue, but was under the impression that that was a ticking that you would hear at idle, and I haven't really noticed this. My noise is more like a rattle coming from somewhere when in the aforementioned RPM range and under load (even moderate load). Truth is, I originally thought it might be coming from the transmission, but I took it to the dealer and they drove around with me in it and said it is spark knock, and that I needed to use the premium fuel. And then it did seem to improve, even go away temporarily when I started with the premium, so that seems to be the right track. But it has by no means vanished altogether.

I'm really hoping I can find a way to solve this so I can start 'investing' in my future happiness with mods, tires, etc.

efan450

If you had a 3.8 i would say yes bad rings and it consuming oil will definitely contribute to carbon build up, but since you have the 3.6 i would say ryan0260's advice is probably the best place to start. Run ccc and seafoam through it. I actually run seafoam through my brake booster twice a year, and hand clean the throttle body ever Season as part of my normal maintenance. Then find a reputable gas station that is constantly busy to buy your fuel from....if they are busy they will always have fresh gas. I would still keep an eye on the head ticking and get in the habit of checking your oil at every fill up.

HornetJK

This is the Cylinder Head issue the early 2012's have been having. It is common with all of the early 3.6 penastars. They have to replace the drivers side cylinder head. It usually is mis firing on cylinder 4. Do some searching on the forum. It is such a problem that the delerships are only allocated one cylinder head per month. It took my dealership 3 months to get one in for mine. Mine was actually mis firing on both the left and right banks, and yes the warmer the engine gets the louder it gets. Your dealership should know what the issue is. If they say they don't they are playing dumb, or theyr mechanics just hate doing the cylinder head job. The dealerships get 70 hrs. of labor from chrysler for the job. It took them about three days to complete mine and it runs great. Power has returned and not having any issues.
Check out these threads,
https://www.jk-forum.com/forums/stoc...t=3.6+penastar
https://www.jk-forum.com/forums/stoc...astar+problems

Ryan0260

Assuming it's not a heat shield rattle, the carbon treatment will be your first logical step. You can get a bottle of seafoam, and a bottle of CCC for just over $20. Give it a try.

boatgeek

Thanks guys,
I'll give it a try at some point soon (swamped with work at the moment). I will say that I don't actually notice any hesitation associated with the noise (like I used to when my old landcruiser was pinging). I did crawl underneath and look for any loose heat shields and everything seemed tight. It was warm on Saturday, and I noticed it seems a bit worse.

I'll report back on the results, may also visit the dealer.

(I did take a couple hour off on Saturday to pull the trigger on some BFG 33" ATs, so this JK and I are in for the long haul. Goodyear SRAs for sale 13k miles, 9/16 tread, if anyone is interested. )

White Ghost

I'm taking my 2012 that has 18k on it to the dealer soon to start an oil consumption test it has grey smoke on start up and on acceleration sometimes and it doesn't quit per like it should. They had bad milling issues in the heads from what I heard and down here in the south a lot of overheating issues good luck.

drich153

I agree. Is your check engine light on? My 2012 is in the shop getting the cylinder head replaced right now.