Engine pinging excessively on 87 octane fuel
JK Freak
Joined: Mar 2007
Posts: 517
Likes: 1
From: Prescott Valley, AZ.
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.
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.
JK Super Freak
Joined: Apr 2007
Posts: 1,699
Likes: 2
From: Lancaster Pa
Believe it or not, I was going to inquire about your gearing and running 33's, and the reason why. To all you guys that said the problem was just being masked by the lower gears, well listen in.
I have a 94XJ 5spd with 4.10 gears running 33's. it has quite a bit of pep, and the engine has never pinged, that is unless I tow my small 18' jet boat, and then hardly ever if I keep in the right gear. Now if I let the engine bog down on a slight hill in let's say 2nd gear, and just give it gas to compensate, I'll begin to ping like crazy. Down shift and it goes away. I could believe that running 33's with the higher gearing and perhaps bogging down on a slight hill then giving more gas to get going, I beleive could cause the engine to ping, and when I read the post, that's what it reminded me of. When the engine is under heavy load, and instead of downshifting to bring the rpm's up, sometime giving it gas just makes the engine ping.
I have a 94XJ 5spd with 4.10 gears running 33's. it has quite a bit of pep, and the engine has never pinged, that is unless I tow my small 18' jet boat, and then hardly ever if I keep in the right gear. Now if I let the engine bog down on a slight hill in let's say 2nd gear, and just give it gas to compensate, I'll begin to ping like crazy. Down shift and it goes away. I could believe that running 33's with the higher gearing and perhaps bogging down on a slight hill then giving more gas to get going, I beleive could cause the engine to ping, and when I read the post, that's what it reminded me of. When the engine is under heavy load, and instead of downshifting to bring the rpm's up, sometime giving it gas just makes the engine ping.