Code P0302 - 3.7L V6 - Where is Cylinder #2?

a4-achtung · 05-13-2010, 08:42 AM

My mom's Liberty just got this code yesterday, the car is running ruff as you can imagine. I had the code checked and it seems it's a misfire in cylinder #2. Can anyone elighten me and tell me where cylinder #2 is located?

oldfamilyguy · 05-13-2010, 01:06 PM

#2 is the front passenger side. a misfire can be caused by several things. maybe as simple as a bad spark plug, when were they changed last? or the #2 coil. fuel delivery problem with that injector also a possibility and other more serious issues relating to poor compression in that cylinder. hope thats not the case, but a comprssion test will tell you.

a4-achtung · 05-13-2010, 01:15 PM

Thanks allot, I was thinking it was the front drivers side. I just changed the spark plugs less than 10k. Hopefully it's just the coil, thanks again for your help.

oldfamilyguy · 05-13-2010, 03:26 PM

Pull that plug anyway, you never know. next switch that coil with another one thats easy to get to and see if the misfire follows it.

a4-achtung · 05-13-2010, 08:05 PM

Well I ended up pulling the plug and it had gas all over it. So I ended up replacing the spark plug since I had an extra one and swapping the coil. Issue persist, I'm guessing the issue might be leading to bad compression. I will be heading to Harbor Freight and getting a compression tester. This is the only code i'm getting so I doubt there is something with the wiring harness, I also swapper the relay for the blower and the ADS. On a side not she has always had an issue with having to add coolant but never being able to find a leak in the engine bay....... Let me know what you guys think from the information I have provided.

oldfamilyguy · 05-13-2010, 10:10 PM

The mystery coolant loss is often internal leaking from a failing head gasket or even a crack. How does the oil look, any sign of coolant mixed in it? I had a similar problem some years ago, but it never set a code for a misfire though so I can't say too much about that. Are you sure thats gas on the plug and not coolant? That would cause a misfire for sure. How many miles on engine anyway and did it ever overheat? Also I believe some of the earlier ones had some valve train problems which also resulted in lost compression. Well the compression test should tell you something more to go by. Good luck with it.

a4-achtung · 05-15-2010, 08:12 AM

Well the reason I don't think it's coolant is because the car doesn't smoke. But of course it could very well be, I still haven't had time to do compression test. I will also be checking the the oil to see if there seems to be signs of coolant diluting the oil. The wiring harness looks great to where it connects to the coil. I guess I will have to see the results of the compression test.

a4-achtung · 05-18-2010, 12:45 PM

Well I did the compression test...... 0 compression in cylinder 2. All the other cylinders are perfect. So I guess from here on out I will have to suggest that she goes to a mechanic. Could it be a bent valve? As I mentioned the car doesn't smoke.

oldfamilyguy · 05-18-2010, 01:30 PM

0 compression = valve not closing. why, that is the big question. some early models had a problem with valves letting go altogether (something with the keepers I believe) and also rockers going bad. If you can get the rocker cover off you might seee whats wrong. Turn the engine with a wrench and watch the valve train at #2, see what you see. Theres a chance it can be looked after with the head on, maybe. Whatever you do, don't start it again, if that valve lets go its into the piston and much bigger problems. I have actually witnessed this myself, it was also on #2.

tjkj2002 · 05-18-2010, 01:58 PM

Quote:

Originally Posted by oldfamilyguy

0 compression = valve not closing..

Not always.Could be a cracked head(combustion chamber),cracked block,bad rings,and cracked piston(or hole in it).Cracked head or block could also explain the constant low coolant.

Told a customer 3 days ago his XJ with the 4.0 I6 had 0 compression on cylinder 2 also,the plug electrode broke off and played hell with the cylinder wall and piston.

oldfamilyguy · 05-18-2010, 11:29 PM

Those other possibilities have been mentioned but I don't know about zero compresion from worn rings. They'd have to be pretty worn. Anyway he's doing alright so far. Checked the first things plug and coil. Didn't have a compression guage so he went and bought one. Now he knows thats the problem, lets not lay on all the worst things it could be. With a little ecouragement he can get the rocker cover off and see what that reveals. Step at a time right? Plenty of time after that for the doomsday report if necessary.

coke_o · 07-17-2010, 01:03 PM

Quote:

Originally Posted by tjkj2002

Not always.Could be a cracked head(combustion chamber),cracked block,bad rings,and cracked piston(or hole in it).Cracked head or block could also explain the constant low coolant.

Told a customer 3 days ago his XJ with the 4.0 I6 had 0 compression on cylinder 2 also,the plug electrode broke off and played hell with the cylinder wall and piston.

My wife has a 2002 Jeep Liberty Limited w/ a 3.7L V6. I keep getting a misfire in cylinder #2. I replaced the spark plug and the coil already but i keep getting P0302 code. One thing i did notice was when i replaced the spark plug, the electrode was missing on it. I didn't think much of it at the time until now that i read this post. Other codes i keep getting are P0455 and P0442. Could this all be related? The car did over heat for a few minutes on two separate occasions. Once, the thermostat turned out to be stuck. The next time, about 1.5 yrs later, the radiator turned out to be stopped up. Now, 1 yr after replacing the radiator, i keep getting these codes. Any suggestions?

bb154 · 07-21-2010, 09:06 AM

to make a long story short....get a compression test done!! I have been fighting with my dealership for the past 15 months about an engine light and a rough ride, first they changed out the O2 sensors, that didn't work. Then it was the plugs. anyway after doing a compression test they found cylinder 3 at 50 PSI lower then the rest and it misfired 72 times in a min. Luckily I had 2400 km left on my powertrain warrenty. 10 days later I have my Liberty back and she runs great!! There is a service bulliten related to this issue.

coke_o · 07-21-2010, 09:33 AM

Quote:

Originally Posted by bb154

to make a long story short....get a compression test done!! I have been fighting with my dealership for the past 15 months about an engine light and a rough ride, first they changed out the O2 sensors, that didn't work. Then it was the plugs. anyway after doing a compression test they found cylinder 3 at 50 PSI lower then the rest and it misfired 72 times in a min. Luckily I had 2400 km left on my powertrain warrenty. 10 days later I have my Liberty back and she runs great!! There is a service bulliten related to this issue.

What did they say was wrong?

aliens8443 · 07-21-2010, 11:13 AM

We had an 02 KJ about a month ago, when just like the ones described above, started running extremely rough. Then one day it just stalled out on me. I thought it was a clogged fuel filter, took it to the mechanic who immediately said it was probably just a bad plug. Turns out it was cylinder #2 that was stuck in the open position with 0 compression. Unfortunately I'm not the most mechanically inclined person, but they quoted me like $1000-1250 to get engine open and figure out why it was stuck open. We were already planning on buying a new Jeep and trading-in the KJ, so that helped us make the decision very quickly. I kind of regret not keeping it and trying to slowly fix the problem, as the KJ still had a few more years left in it. Good luck trying to figure it out though