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I have a 2002 Jeep Grand Cherokee and my check engine light is on. The codes say I have a cylinder 2 misfire.  The car shakes as I depress the gas pedal and get around 40 - 50 miles/hr then when I get higher than that it may start to jerk when the rpms get around 3000 and I loose power. When this happens I have to let off the gas pedal and let the rpms drop. I then depress the gas pedal lightly and let the car gradualy pick up speed this is a hard problem when driving on the highway when you may need to accelerate quickly.  I have changed the ignition coil and all my spark plugs, I also did a coolant empty and flush and put some blue devil liquid gaskit sealant in my radiator.  This did not help.... I use my car to travel quite a bit and any help or direction would be GREATLY appreciated.   Thanks for your help.  

compression test first.......  

if you have a burned valve... or a blown head gasket.. sealer is not going to help...

you may also have a clogged injector...    what did the spark plug look like on the #2 cylinder???    was the cylinder end white or black and covered with carbon...   or yellowish...   normal would be a light tan...



is this a 4.0 six .... with the LONG ignition coil....   did you also install new spark plug boots??? and use silicone dielectric or silicone spark plug boot lube on the inside of both ends of the boots...

have you checked the battery terminals for being totally clean...    to the point of taking them off and wire brushing and washing off with hot water only any corrosion and hard crusty lead... i usually have a battery terminal scraper instead of a brush..

while you have the battery disconnected.. clean the ground wires at the engine block...

you may want to invest the 10 to 15 bucks in the small battery powered device to plug into a lighter socket to keep the various memories alive while you have the battery off...  this also prevents the erasing of the trouble codes and the data they store...


there have been several problems with the crank sensors... but usually it will be a no start... but a misfire is also possible..
the crank sensor is usually back under the motor as it is triggered by a notched ring on the flywheel...  

Before I put in the sealant I was getting some white smoke and some what looked like oil or coolant (black drops of liquid) out of the tail pipe when I turned on the engine. I don't get that now but the car still shakes around 40 - 50 mi/hr. I put sea foam in the oil and in the gas tank to treat the injectors.  And I also have the long ingniton coil that you spoke of, I did also install new sparks and  plug boots, and used silicone dielectric or silicone spark plug boot lube on the inside of both ends of the boots. I also cleaned my battery terminals. When I took the spark plugs out the ends looked kind of tan to orange in color. I'm thinking about getting a gaskit kit and replacing the gaskit myself but I never done it before.  I am thinking about buying the Jeep Cherokee book and look it up and see how to do it.  I don't know what else to try. Any more thoughts on this and thanks for your help.  

is the coolant orange or green??????/    if the coolant is orange.. and the spark plugs are orange.. you may have a coolant leak..


i really think that i would do a compression test first..      that will tell you a lot..    but how..

if all the cylinders have within 5 to 10 pounds of compression when tested... you may have to look elseware..   some parts stores like AZ have compression testers in their loan a tool section..   most compression testers are less than 25 bucks..

if you had a remote starter switch.. and a air compressor...  i would have you rig up your compression tester hose with the valve core out of the end.. (so air can be pushed into the motor..)   with proper quick adaptors on the end of your compressor hose to hook up ....   then take out one spark plug at a time.. put the compression tester hose in.. use the remote starter switch to bump the engine around till you get it to top dead center on that cylinder.. then charge the line with compressed air.. while watching the coolant level.. if the coolant level rises... when you charge the cylinder with compressed air..  you have verified a compression leak into the cooling system...    warning.. the engine will kick around  when you apply the air if the cylinder is not at top dead center.. .. don't worry...  just reset and try again...    

this has been done with a tool called a cylinder leak down tester..  but there is a restriction in the end of that hose ..  so the test is not as accurate for this exact test..  


when i showed this test to my boss a few years ago.. he had been fixing cars for close to 45 years..  he was amazed..



there are also several 4 wheel drive magazines on this site... and they have covered replacing the heads on 4.0's several times.. i will try to find some of the articles later today..  do check back....


http://www.jpmagazine.com/index.html



you might find the history of the jeep 6 interesting..

http://www.jpmagazine.com/techarticles/engine/154_0604_jeeps_kick_ass_engine_history_4_liter/index.html



this is what i was thinking of....   it is a 4+ part article on rebuilding the 4.0 jeep motors..   more info than you need.. but important to add to your knowledge base..

http://www.fourwheeler.com/techarticles/engine/129_0711_1987_2006_jeep_40l_inline_six/index.html