Just joined this great forum and been reading up all afternoon. Shocked to see all the folks with the cracked cylinder heads. I thought mine was the only one loosing coolant and I'm glad I didn't take it apart hoping it was just the head gasket. Anyway, mine is a 2000, bought new and now with about 180K miles. It is basically my winter car here is northeast. I first noticed the coolant loss/oil level increase a few weeks ago. The is plenty of info on the head issue so I don't want to go there but my real question is about the engine light. It came on a couple of days ago and the code is P0304; cylinder 4 misfire. So I replaced the plugs and the car ran OK for a bit and the light came back on, sometimes steady and sometimes flashing. With the light flashing the engine begins to shake and acts just like running on five cylinders. Before reading all the posts here, I almost ordered a coil pack thinking the cyl 4 coil was going bad. But now I am wondering this is another casualty of the leaking head.is there a good way to rule out the coil pack? Also, is there a trick in removing the connector going to the back of coil pack rail? I spent about an hour trying to figure out how to remove that connector wit no success. Thanks everyone and sorry about the long post. I wished I had discovered this forum earlier. But I must say this is the first time the Jeep is giving is type of trouble. It's been one of the best cars I have owned. Thanks I advance.

 

first thing I would do is check your oil for coolant. Also pull your oil fill cap and look down inside to see if you have any brown sludge in there. On your 2000 you have the 0331 head that crack between 2 and 3 cyl and a lot of times you can see the crack in there.

 

Actually the 0331 head casting defect is between cylinders 3 and 4.

And because of that, it is likely that your cylinder 4 misfire is related to a cracked cylinder head. You have the other major symptom of a cracked 0331 which is coolant loss from the reservoir.

Sorry to report, but I'd get a diagnosis quickly as if it truly is a cracked head, the longer you run the engine, the more damage you are doing to your engine bearings.

 

Oops I didn't realize that I put 2 & 3. Thanks for catching that.
Like tjwalker said

 

The Flashing Engine light means serious misfire detected...that's why it's shaking like it's "running on 5 cylinders"...because that is exactly what it's doing. The flashing light means you're about to send your cat converter to the great scrapyard in the sky.
The plug is no doubt fouling from the leaky head, runs fine for a short while after replacement, then fouls out again.
Check with Clearwater for a replacement head.

 

Definitely sounds like a cracked head... check oil for coolant immediately.

A defective coil pack *should* manifest on adjacent cylinders as they're paired up. When cylinder 3 gets a main "power" spark, cylinder 4 gets a secondary "waste" spark to ignite anything left over.

 

Thanks everyone for the replies. I have no doubt I have a leaking head. I just did not realize it could be cracked as opposed to a bad head gasket, specially since the car has never overheated and the heater works just fine. The other thing is the plugs did not look badly fouled when I replaced them yesterday. And they had been in there for quite some time. Regarding the misfire, is there any way to rule out the coil pack other than just replacing it? The misfire just happened all of a sudden. That's why I suspect the coil pack. Also, is there a trick for pulling the coil pack connector off? Real tight space back there to see the clip, etc. Thanks again for your help.

 

While an overheat of an 00-01 almost guarantees a cracked head, it is definitely not a requirement.

Many without an overheat and that have practiced good cooling system maintenance have suffered with the cracked head. I really do think that is going to be what you're going to find here.

The misfire you are experiencing IS most likely directly related to your cracked head.

 

Well, I am going to deal with the head issue soon but right now I need to get the car inspected and need to fix the misfire issue. This is mostly a winter car and I'll have time to address the bigger issue between now and then. Just don't want to replace the coil pack and end up where I am now...

 

Well, since winter is over it's time to do the right thing. Stop driving the vehicle! You are not just damaging the spark plug, you are destroying the entire internals of the engine. If you continue to abuse it for any longer you will need to replace the entire engine, not just the coil pack. I suggest you begin using some common sense and fix the real problem.

 

Actually my common sense is telling me that based on the condition of the plugs, smooth running condition of the engine right before the misfire code/engine light, and the mileage of 180K, the culprit is probably the coil pack. Of course the leaking head needs to be fixed. No question there. My only dilemma is that the three coils fire two plugs at any given time with one spark going to waste. The same coil that fires cyl 4 fires cyl 3 so I should expect the misfire on both not just one if the coil is bad, e.g., P0304 and P0303. Am I thinking right? In theory coil issues should affect a pair of cylinders not just one.

 

^^X2^^
I wouldn't even bother with the inspection until you fix the head problem. That would be my main concern. But, that's just me.