First of all I want to thank you all for the great collection of information posted on this site. Earlier this year the TSB information helped me diagnose a clutch problem and get the dealer to replace the clutch and throw-out bearing under warranty.
My question today has to do with engine pre-ignition (pinging). I have a ’08, 20K miles, 6-speed, that is bone stock except for 33” tires. When I’m using 87 octane (10% ethanol max) per the owner’s manual it pings excessively during the summer months, to the point where I have noticeable power loss climbing hills at highway speeds. So I have to run 89 or 93 octane during the summer to control it; however, the owner’s manual states that some amount of pinging is “OK” and that premium fuel and octane boosters should not be used due to risk of some unspecified damage.
First of all it seems really strange that it would be “OK” for any engine to ping and it seems to have gotten worse over the last 10K miles. I’ve tried using fuel injector cleaners, a fresh clean air filter, and water-wetter in the radiator to help with the cooling, but there was no real change in the amount of pinging. One thing I have not tried yet is cleaning the MAF sensor. Perhaps a little dirt there is causing it to run a little lean which can create a tendency to ping. I never get a check engine light or any indication the service is required, just pinging.
Any body else struggling with this, and if so, what solved it?
Thanks.

 

I have the same issue. I'm still a stock '08 auto. What about running cooler plugs?

 

Try replacing your knock sensor!

good read
https://www.jk-forum.com/forums/show...t=knock+sensor

 

The pinging sound you hear can be an indication of a couple of different things that are wrong--real pre-ignition is rare and is caused by a defect in the firing cylinder, such as a piece of hot metal stuck somewhere igniting the gas/air mixture prematurely. Detonation, which is much more common, is caused by gas with too low of an octane rating for the engine tune/compression/spark plugs in use. I suggest that you read this article and consider the possible troubleshooting avenues it suggests ...

http://www.misterfixit.com/deton.htm

 

this may not be your issue cuz yours sounds more like a ping. but i was having a ping/rattle under the hood that has been driving me nuts. i went to the knock sensor link and found a idea to check heat shields on exhausts. that wasnt my issue but i did find the exhaust was loose between the header and the pipes. its located behind your inner fender walls and is a easy access with a 15mm wrench.

it was a easy fix for me and no more noise.

hope this may help someone with a noise under hood

 

Mark, You're right, I'm wrong. I should have specified "detonation" as my issue.

TripleJeep_99, Thanks for the excellent link. After reading it I'm absolutely certain my knock sensor is bad. I've got all the symptoms, especially cruising at highway speeds (2300 RPM) and it needs a little more throttle to get up a hill, the detonation gets rampant. Looks like I'm heading out to get a knock sensor this week.

Thanks again y'all.

 

Yeah, a few people have had issues with the knock sensor so that would be worth checking. In my case it was fine; my V6 just rattles and pings under load when I run with regular gas so I use mid-octane premium gas (and pay extra for it over regular of course).

I know Chrysler specifies regular unleaded as the minimum requirement but as has been stated here before on similar threads, many are finding that these motors do run better on mid-octane premium gas.

At the moment I have regular low-octane unleaded in the tank (was at a remote location yesterday & all they had was the low octane stuff) and sure enough she's rattling again like a tin can full of marbles every time I put a bit of load at low RPMs on her. I'm getting noticably less mileage as well as the knock sensor detects pre-ignition & starts retarding the timing thus resulting in power loss and less mileage as I plant my foot to the floor to compensate.

 

Friends, So that others may benefit from my experiences I wanted to post an update on my progress with this issue. The good news is that the issue is solved. You need to know that my jeep is an '08, 6 speed with 33" tires and was running the stock 3.21 gears. I ran those 3.21 gears with 33" tires for about 20,000 miles. For the first 10,000 miles I had no problems other than 6th gear was completely useless. Later on the engine pinging started and got progressively worse whenever I had to climb a hill at hiway speeds or take off from a stop lite at a steep incline. I did replace the knock sensor as was suggested. I also had the dealers mechanic completely go through everything looking for an explanation. They came up with nothing. I replaced the spark plugs, airfilter, ran fuel system cleaners etc. all to no avail. What finally solved it was swapping my 3.21 gears for something different. I chose to go with 5.13s. The end result is that I've got plenty of power on tap now and the pinging has stopped.
So the theory is that running 33" tires with 3.21 gears is OK for a little while, but it was lugging the engine excessively which lead to carbon build-up and created my pinging problems.
So now I have 5.13 gears. In 6th gear I'm turning about 2950 RPM to cruise at 65 MPH with 33 inch tires. It's a little high I know but the upside is that when these tires wear out, I'm ready to move to 35" tires which will make the RPMs more reasonable. If I had planned to stay with 33" tires forever I probably would have gone with 4.88 gears instead of 5.13s and got the same effect.
So in summary I don't recommend trying to run 33" tires with 3.21 gears as a permanent situation. You may get away with it for a while but it takes a toll on the engine to load it that much routinely.
Happy Motoring Amigos.

 

hmmm...I have an '08 2dr as well, but its a rubicon with stock tires and 4.10s. It pings all the damn time with 87 octane. Summer, winter, uphill, flat ground. It absolutely does not matter. It sounds like I have a coke can full of quarters under the hood every time I accelerate. It doesn't matter what gas station I go to, but 89 does make a noticeable difference. Maybe the knock sensor will help me because gearing is obviously not my problem.

 

So realistically you would still have knock in the lower rpms in a higher gear. The new 5.13s just brought u up enough in your rpm band to avoid where it was knocking lower.

So you masked the problem and didn't really solve it.