Misfire Mystery

[jtcowman]

Hello all,
I have read many posts on this topic, and since most of them seem to be old, I thought I would start fresh and see if anyone has found a solution for this problem. I am working on a 2002 Jeep Liberty Sport, V6, with approx 180000 miles on it. About 3 months ago, I was driving on the highway, Liberty running fine, when it started missing like 2 cylinders had dropped out of it. It acted like a severe miss, and had no power. The check engine light immediatly came on, and when I would try to go up even the slightest hill, it would start flashing. When I got it home, I had an Autozone check it, and the codes indicated a misfire on 5 and 6. I changed the plugs and coils for both cylinders. #6 plug looked OK, but #5 plug had the tip and the electrode blown off of the plug. Changing the plugs and coils made it run much better, but the check engine light remained on, and I still had a slight miss. I checked the connection where the plug attached to the coil, and it did not seem to be locking in place on either side, so I zip-tied them securely in place. This also seemed to help, but the check engine light remained on. I have been trying to find out what this problem is, but haven't been too worried about it because the engine seemed to be running fine. Then tonight it started missing again, with the check engine light flashing at me whenever I put a load on it. We stopped, went into Walmart, and when I started it back up it was running fine. I have read about changing crankshaft sensors, ASD relays, cleaning fuel injectors, detecting vacuum leaks, but there does not seem to be any definite answer. Has anyone found an answer to this problem? Any help would be sooo appreciated. I am not a great mechanic, but I would like to try anything I can do before I cash in my 401k for the mechanic! :secret:
Thanks for your help, Jim

 

[KodiakKJ]

I had a cylinder six misfire last week. It was fine for two months, then I power washed the engine. The bolt that holds the coil pack on was loose enough on mine that the coil pack was barely on the spark plug and it let water in. That may not be it for you, but it is a place to start.


Sent from my Lumia 1520 using Tapatalk

 

[02blue]

First thing I'd do is buy an inexpensive code reader that allow you to read and clear codes. Usually can get one for 30 bucks or so. Unless you clear a code the CEL will remain on for a period of time even if not active. What are the codes now? Same? I'd fix the connectors. I wouldn't trust running around with zipties. The sensors and relays are not expensive but I hate throwing parts at a problem when it could just be the connectors. Can't really explain the burned up #5 but how old were those plugs and what type before you changed them? You'd probably be wise to take it in and have a full scan done. Sounds like a number of possibilities and sometimes you have to pay to play.

I like the Techron injector cleaner. Wouldn't hurt but probably not the issue.

I threw a violent #6 misfire way back after changing a radiator. Cleared it and let it sit an hour. Never came back. About 10,000 miles ago.

 

[tjkj2002]

Hello all,
I have read many posts on this topic, and since most of them seem to be old, I thought I would start fresh and see if anyone has found a solution for this problem. I am working on a 2002 Jeep Liberty Sport, V6, with approx 180000 miles on it. About 3 months ago, I was driving on the highway, Liberty running fine, when it started missing like 2 cylinders had dropped out of it. It acted like a severe miss, and had no power. The check engine light immediatly came on, and when I would try to go up even the slightest hill, it would start flashing. When I got it home, I had an Autozone check it, and the codes indicated a misfire on 5 and 6. I changed the plugs and coils for both cylinders. #6 plug looked OK, but #5 plug had the tip and the electrode blown off of the plug. Changing the plugs and coils made it run much better, but the check engine light remained on, and I still had a slight miss. I checked the connection where the plug attached to the coil, and it did not seem to be locking in place on either side, so I zip-tied them securely in place. This also seemed to help, but the check engine light remained on. I have been trying to find out what this problem is, but haven't been too worried about it because the engine seemed to be running fine. Then tonight it started missing again, with the check engine light flashing at me whenever I put a load on it. We stopped, went into Walmart, and when I started it back up it was running fine. I have read about changing crankshaft sensors, ASD relays, cleaning fuel injectors, detecting vacuum leaks, but there does not seem to be any definite answer. Has anyone found an answer to this problem? Any help would be sooo appreciated. I am not a great mechanic, but I would like to try anything I can do before I cash in my 401k for the mechanic! :secret:
Thanks for your help, Jim

There is no set answer for misfires,many causes that you must eliminate 1 by 1.




Never drive it when the MIL is flashing,damage is being done to the cats which by the way can cause misfires(damaged cats).

 

[kage860]

My opinion is if the first two spark plugs looked bad, replace the other 4 spark plugs as well, they're inexpensive. As o2 blue says, get a code reader. I would check in this order:
1. spark plugs
2. fuel pressure

The reason I say fuel pressure is you had a problem when going up hill, could be pump or fuel filter. Harbor freight sells a $20 fuel pressure gauge. Check pressure when idling and under load in park (throttle pedal pressed). The shop manual for my 07 Jeep Liberty 3.7 says fuel pressure should be 59 psi (within 5 psi at least) .

Don't change sensors/parts that aren't wear items until you finish your diagnosis, you don't want to make any new problems. Don't give up.
Let us know how it goes.

 

[Jacob Ivey]

Just as a heads up for helping out anyone with p0300 and the misfires being on 1 3 5

Bank 1 sensor 1 o2 sensor causes this issue you're welcome lol