IBlameTheDog
NAXJA Forum User
- Location
- Arizona
First off thanks to Billy Baker and Mdub in the Arizona forum for giving me some ideas to look for.
At first it sounded like a rod knock but I was not convinced so I set off to eliminate everything else. First thing I tried was changing the oil and adding some Slick 50 and that did nothing for the noise. Second I made sure the torque converter bolts and exhaust was tight and they were so that did nothing. Then the last thing I tried was to decarbon the combustion chamber and whala!!! Sounds like a Jeep now instead of a Cummins. I have to admit I liked the sound but knew something was wrong.
All I did was take a bottle of Sea Foam from Auto Zone and take off a vacuum line close to the throttle body and added 3 feet of rubber line. Then with the engine at normal temp and running I allowed it to suck in the Sea Foam into the engine through the intake manifold. I had to slightly pinch off the rubber line so it would only suck a little in and keep running. Then I allowed the Jeep to sit with the engine off for 20 minutes then started it up and run it around the block at high RPM until the smoke quit coming out of the exhaust. When I pulled it into the driveway the knock was gone. I repeated the process one more time to make sure it was nice and clean.
So the bottom line was that there was so much carbon build up inside the combustion chamber that it was causing it to knock at idle and just above idle. This was a known issue on the old 258 motors in the CJ's and early Wranglers but I have not run into it on the 4.0.
Anyhow I hope this helps someone else out because I almost put a new engine in this and for 10 dollars I saved 1000.
At first it sounded like a rod knock but I was not convinced so I set off to eliminate everything else. First thing I tried was changing the oil and adding some Slick 50 and that did nothing for the noise. Second I made sure the torque converter bolts and exhaust was tight and they were so that did nothing. Then the last thing I tried was to decarbon the combustion chamber and whala!!! Sounds like a Jeep now instead of a Cummins. I have to admit I liked the sound but knew something was wrong.
All I did was take a bottle of Sea Foam from Auto Zone and take off a vacuum line close to the throttle body and added 3 feet of rubber line. Then with the engine at normal temp and running I allowed it to suck in the Sea Foam into the engine through the intake manifold. I had to slightly pinch off the rubber line so it would only suck a little in and keep running. Then I allowed the Jeep to sit with the engine off for 20 minutes then started it up and run it around the block at high RPM until the smoke quit coming out of the exhaust. When I pulled it into the driveway the knock was gone. I repeated the process one more time to make sure it was nice and clean.
So the bottom line was that there was so much carbon build up inside the combustion chamber that it was causing it to knock at idle and just above idle. This was a known issue on the old 258 motors in the CJ's and early Wranglers but I have not run into it on the 4.0.
Anyhow I hope this helps someone else out because I almost put a new engine in this and for 10 dollars I saved 1000.