I bought a friend's 2011 Jeep Liberty with 197,000 miles however it's throwing P0300 & P2302 codes. New plugs and coils were installed before I bought it and I checked them today; checked gap also and were fine. I did notice that the #1 plug seemed a bit darker than the other 5 plugs (2nd pic). I swapped coils around, along with plugs and the codes remain. The fuel trims are all at 0, the O2 sensor heaters seem to be functioning at around 1400* according to my scanner tool. One of the things I've noticed is that the #1 coil has a tiny cut in the wire and perhaps this would cause the trouble codes? I also listened to the fuel injectors and got a consistent clicking on each one, including the #1. What else should I look for?
What brand coils were installed? If the coils were replaced with anything but Mopar brand, replace them with Mopar. Plugs should be NGK ZFR6F-11G copper core only. Libertys are very sensitive about these parts.
Several of the old hands on the Jeep Liberty forum suggest disconnecting the battery connections and taping them together for about 30 minutes to reset the system. I’m a recently new owner of an ‘02 Liberty with the 3.7l too.
I pulled the +cable off for more than 24 hours, but perhaps that doesn't drain the capacitors in the PCU like touching the pos cable to the neg and discharging them that way. I had read about that and will try it and see if it changes anything. This morning I also ordered a Mopar crank position sensor and a cam position sensor at about $66. I'm still in much cheaper than a proper diagnostic and/or PCU and at this mileage, they're probably close to being due anyway.
I have had 3 of the 3.7 Mopar motors and all had a slightly uneven idle that I chased with tune up parts and sensors , but they all ran great for many miles... Your 200,000 mile liberty , with the new dark colored spark plug, may need some valve stem seals or ? Anyway my 2011 Liberty has been easy to work on and at 100,000 miles , is pretty fun to drive , for cheap transportation ... Good luck and enjoy it
Good to hear they work well for you. If it comes to pass that it's a headgasket issue, I'll have the heads rebuilt entirely which will take care of the valve stem seals. In my research I've seen others that have put 12 port fuel injectors instead of the 4 port and have seen increased mpg's and hp, but that's definitely after I get this running correctly. Even so, I'm not ruling out a clogged injector yet, despite all of them clicking consistently by ear.
and is it the same cylinder all the time? if yes, clean all the connectors between the coils and the ECU. if it's the same cylinder, then its time to compression check. do a leak down too if it always cokes up #1, even when swapping components it's the cylinder, its not the systems, its the cylinder. I was gonna say maybe a gasket/manifold leak but those usually make it lean and don't really coke the plug. I could be wrong. and I can think of why... maybe borescope the pistons through the plug holes. there is an Iphone app/attachment that sells for like 20 bucks and is amazingly good
So I cheated a couple weeks ago and took it in to a new shop for a diagnosis. They cleaned some plugs, cleared codes and told me to pick it up. $145 later I drove it home half expecting an engine code to come back on. Sat on it until yesterday when I plated it in my name and drove it around today about 30 miles and all seems well. I'll update this if something comes up soon, but if it hasn't already I'm pretty sure it won't. In any case, I like this vehicle and although it doesn't ride as comfortably as my Grand Caravan, it's slightly more compact and has a much higher towing capacity if I decide to put a hitch hauler on the back.
After approximately 400 miles the issue came back and last week I took it back in to get it checked out. Turns out they're replacing the PCM and hopefully I'll have it back today, but possibly Monday.
