I’ve done some searching and not seeing much that’s being helpful.

It’s a 2001 coil on plug.

To start off. A few weeks ago I was cruising along on the deer lease and bam high centered on a stump. Wasn’t a hard hit, the front axle bumped right over it but the exhaust didn’t fair quiet as well. It caused a slight exhaust leak at the manifold/ y pipe connection. Well on the way home I pulled up to a stop sign and it just started running bad and went into limp mode. I made it home. Parked it until I could play with it. My dad tightened the exhaust up a little while I was gone to work(2 weeks on an oil rig) but still not enough.

It only seems to do this on deceleration or stopped. Runs great going down the road. I can switch the engine off and back on and bam she’s back to running like a top. I messed with it under the hood and can’t find anything that looks out of place or loose.

Well yesterday I got a code scanner and pulled a p0300, 301 and 306.

Could there be anything small that I’m missing? Just seems really weird that it started right after I hit this little stump.

 

It is possible that your new misfire could be coincidental to your run in with the stump. Regardless, troubleshooting code strategy is the same. P0300 is a random misfire, P0301 is cylinder 1 misfire and P0306 is cylinder 6 misfire.

1. With any random misfire, the first thing I do is to verify fuel pressure. For a 2001, you should have 49 psi, plus or minus 5 psi.

2. If memory serves me correctly, there is a direct relationship between cylinders 1 and 6 via your coil rail. Below is a link to a thread of another XJ with similar cylinder misfires. Do some Google searching with "Jeep Cherokee + codes P0301 P0306" for more light reading.

https://www.cherokeeforum.com/f2/cyl...isfire-147015/

3. For any misfiring, spark plugs are of course in play, (when were they last changed?) but my gut feel here with your situation is that the coil rail and or associated wiring might be involved here.

Good luck and keep us updated!

 

Before you do anything else, I would clear the codes and see which ones come back. When the '00-'01 computer encounters a misfire problem, it will often pitch a tantrum and throw extraneous codes as it tries to adjust to keep the Jeep running. If you clear the codes and only one comes back, that can help you narrow the focus of your troubleshooting.

 

Could it have done any damage to the 02 sensor system to maybe cause this? Broken wires? exhaust pinched and restricted?

 

I realize this is an old thread, but my 01 4.0 wj is doing the exact same thing and I've tried everything to fix it. Misfire p0300 p0301 p0306 and flashing engine light with loss of cylinders 1 and 6 (assuming limp mode from cyl 1 misfires) it only happens on deceleration. So far full tune up, CPS, crank sensor, iac, GPS, map, speed sensor, ecu, and injectors changed. No improvement at all... any help at all would be greatly appreciated.

 

Yo, did you ever figure out the issue? I'm having the same problem. New engine, no vacuum leak and perfect fuel pressure in idle/accessories mode/running, new injectors, new IAC/TPS/CPS/throttle body, new oxygen sensors (I have 4), no distributor/spark plug wires, new pre-gapped spark plugs, new ingition coil pack, grounds are clean, battery and wiring is new, no frayed/fried wires as far as i can tell. I'm looking at maybe getting a new camshaft synchronizer, but otherwise I'm lost. No other thread seems to have the exact symptoms I'm having, and the only codes are for the misfires. I've put too many hours into this beauty to let her go now.

 

I’m in the same boat, to the point that what you wrote could have been about my Cherokee! I can’t even count how many hours I’ve spent on this truck. I’ve also replaced the engine wiring harness to further try to eliminate a wiring issue. When prior issues pointed to the pcm I replaced that to no avail. I don’t mind the cost so much because I like the challenge but considering throwing in the towel as other projects are suffering due to lack of time. If I keep going I’m considering replacing the head and while it is out going over every single wire again.
I kinda feel like someone with ore advanced diagnostic equipment like a scope could do some deeper diagnosis but doubt most shops are interested in racking up a lot of diagnostic hours on my dime if they don’t think they can solve the problem based on a few conversations I’ve had.

 

I have a suspicion it has something to do with the evap system, perhaps the charcoal canister. Cause the problem is worse right after filling up and doesn't happen in neutral, I only just realized this last night. But I had some hoses go out right at the canister and had a leak for a while before I realized the hoses were crumbling. I'm thinking maybe water in the canister, but don't know **** about the evap system. Perhaps someone more experienced could delve into that or correct me.

 

Any update with your problem?

 

[size=16px]The problem started happening even in neutral. No codes, no CEL. Can prevent it if i rev over 2500 as im decelerating, but even then itll occasionally happen. Sometimes itll be fine as im stopping, only to rev and misfire as im idling. Worsens or happens more frequently when my AC is on. Potentially exasperated by a faulty IAC. Still no vaccuum leaks as far as i can tell. My roommate (mechanic) suggested timing belt, but no difficulty starting and no stalling. Camshaft sensor replaced but not the synchronizer (i have an aftermarket pulley so idk how to find dead center to change out the synchronizer). No improvement with just the sensor. Seems the worsening after filling my tank was a fluke, it doesn't seem to affect anything. Checked the evap system and it's not clogged. My cats are bad, but my 02 sensors are new and not throwing any codes from them. Unchanging whether it's a cold start or she's been driven and warmed up already. Sometimes it happens once a day, sometimes it happens every time I stop. No correlation to how I'm driving or traffic or whatnot. Can't do any further tests because ole Betty is out of commission until I replace her transmission (unrelated to the aforementioned symptoms). Any advice is welcomed, im no mechanic and barely know what im doing. [/size]

 

Well you seem pretty well versed on your Cherokee and what items to suspect that’s for sure. I was hoping you found something that may lead me to solving the same issues. I’ve given up on it.

 

I try my best to figure it out on my own, but im really just doing process of elimination. DM me, if you can. We can update each other on any changes, symptoms, etc.

 

It ended up being my camshaft synchronizer! So sorry I didn't update sooner.

 

Glad to hear you figured it out. Hope to get back to looking at mine in the spring. I’ve replaced the camshaft synchronizer in the past but figured I’d start there because it’s easy.