Cylinder 2 misfire

T

Tan2TheMan

New member
I have been running into the issue of cylinder 2 misfire on my jeep rubicon with the 4.0 in it. I have already replaced all the spark plugs with new ngk plugs but that didn't help at all. I then put injector cleaner with premium fuel and that helped a little. The jeep was sitting for about a year because I had a broken transfer case. I just need some help fast because I need to drive it for work but I can't get it to pass inspection.


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Just a guess your valves are sticking from varnished fuel since it sat. Get some good decarbonizer like BG 44k or a kit where you can run the carbon cleaner through a vacuum line.
 
I've heard of I6 cylinder heads cracking which will cause a miss, but if it only has 3,000 on the engine then that's probably not likely.
 
Just for an update, last night I compression tested the motor and all were 150 psi but cylinder 4 was 120psi and cylinder 2 was 90psi. I also swapped the injectors from 2 to 5 to see if the misfire moves with that injector


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Is there any unusual noises from the engine? 4.0's have been known to bend push rods. With it sitting for a while a lifter may not be pumping up. Both of those would generally cause a valve train noise though.

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Cylinder 2 should not be that low.... The cylinder heads cracking on these are a very common problem from what I have found recently talking with people about my 4.0 build. Titan Engines out of Florida sell rebuilt motors but they specialize in the Jeep 4.0 and the Jeep 4.0 Stroker motor. they sell reman heads for like $300 and a new casting designed which takes care of the flaws in the head that cause them to crack and have issues for $450. I just priced this out this week. Not saying you need a new head but like WJCO said... If it has been sitting you probably have varnish built up on the valves. or you could have a bigger issue. Could maybe be a lifters sticking or more serious. Seafoam through vacuum line could work.

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Pretty sure 90 psi is still enough to fire, was the engine warm when you did the test? How long is your new engine warrantyd for?
 
Pull the oil pan and look for a cracked piston or broken piston ring. Or like the other guys said, pull the valve cover and rocker arm assembly, pull the push tubes and lifters, clean them out, and reassemble.

Also, could be a blown head gasket. If you have a cooling system pressure tester (or know someone with one) perform the test in the video. Loss of compression has to go somewhere! https://youtu.be/SFEBI2c1-Lg
 
A busted piston skirt wont necessarily cause loss of compression because it generally breaks below the rings. It will however cause a noise. I had a skirt bust on cylinder 2 oddly enough, and compression was fine. It actually sounded like a bad lifter.





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It doesn't make any noises and I realized that it will only throw the code when it idles for longer than a minute or two. But when I drive it it has normal power and it doesn't sound like its misfiring


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