I've had my jeep, a 2000 Cherokee Sport 4.0 4x4, for a few months now. Its got 194k. A new issue has popped up and I need some help knowing how to proceed.

A few days ago I got the flashing CEL. I swapped in 6 brand new spark plugs and for a couple days it went away. Last night it came back. Today, I went and got the codes run and its a laundry list. (P0300, P0301, P0302, P0303, P0305, P0158, P0155, P0161).

Additional, possibly helpful info
- the lines to the o2 sensor under the jeep are cut. I haven't gotten around to fixing that yet, but I certainly need to.
- this problem is intermittent. Today, when driving home after having the codes run, the light quit flashing and power came back. This has happened a few times. I haven't driven it long enough with this issue to see if the problem reappears at some point after going away.


Having admitted I suck at diagnostics, here's what I think could be my issues. Convince me of one, all, or none of the and offer up your explanation. I can turn a wrench. I suck at diagnosing.

1. Ignition Coil
2. Injectors
3. Catalytic Converter crapped out causing pressure issues

What else could it be? How would you go about chasing this?

 

Some of those codes indicate O2 sensor voltage problems.
You already know the O2 wires are cut. Cut for a reason?
Most of the other codes indicate cylinder misfires.

Change the O2 sensor, probably the cat too, fix the wires, clear the CEL codes then take it from there.

 

You have three codes that point to an O2 sensor problem, and this^^.

Why are you looking at anything else before you fix this obvious problem?

 

I've been running it since I got it with the o2 sensor out. Cut is the wrong word- torn, like something grabbed them, is more accurate. I was told the O2 sensor was out when I got it and like an idiot didn't crawl under there to look myself. I assumed out meant not working. I'm investigating other options because this issue is new and the sensor has been that way for as long as I've had it (December), and because changing out spark plugs seemed to make a difference- if only for a few days. I appreciate the input- the sensor will be purchased and installed tomorrow, but there's my reasoning.

 

Changing the spark plugs made a difference because the old ones were carboned up from running stupidly rich. The new ones quickly followed because the lack of the O2 sensor input to the PCM has you running stupidly rich.

Fix obvious, real problems before chasing theoretical problems.

 

Thanks, and I'm learning here so bear with me. Why would the old plugs be fine for months and the new ones (same make/model plug) crap out in a couple of days under the same running conditions?

And I will be picking up an o2 sensor and popping it in place tomorrow, so updates to follow.

 

The front o2 sensors are prone to getting wrapped around the driveshaft, I would imagine that's your problem. After replacing a new one, make sure you zip tie it up in a suitable position, on my 2000 their is a little plastic bracket to hold it in place and I zip tied it into place there

 

I got the o2 sensor installed today. Then I pulled the ignition coil just to double check the spark plugs- problem found. I pulled all of the plugs to double-check gaps and see if any of them had suffered any significant wear or damage since I put them in just a few days ago. I bought a torque wrench and discovered that every single one of them was much looser than specified, including one that it would seem I flat forgot to tighten after setting it finger tight. It had wiggled out even further. Now, I've only driven it a few miles since doing this, but as of now, all is well.

 

A brief moment of hope and then...

driving home tonight the ride got rough, the CEL came on and then started flashing. Back to Autozone to run codes tomorrow. Update to follow.

 

Beware of aftermarket sensors on these beasts. They are very picky. Even Bosch O2 sensors have problems with them, and normally Bosch is top of the line.

Stick with NTK/NGK for sensors. Yes, they cost more, but the other stuff has so many horror stories that it's just not worth it.

 

When the CEL starts flashing, youve got a misfire, and you should not drive it any more than absolutely necessary. Misifres are very bad for an engine. Buy yourself a code reader and keep it in the glovebox so you dont have to limp it to Autozone to have it read. I use an Actron Cp9670. It can also read live data, which is a plus.

 

Fortunately for me, Autozone is only a few blocks away. Even still, a code reader went on order this afternoon as soon as problem resurfaced after only a few hours. I'm hoping when the codes are read tomorrow, I'll have at least cleared the o2 sensor issue. If not, at least I'm at the place where I bought it so I can crawl under the car real quick, take it out, and swap it for something else.

 

New information-

I got up a bit early this morning to take another look at it before work. I discovered that when the engine mount was fixed a few weeks ago, the shop trapped the o2 sensor connector between the block and the pre-cat, melting it into oblivion. I pulled and clipped that to get ready to replace it.

I had also, while it was running, pulled injector connectors to see if I could find the source of my misfire. I can pull the 5th injector connection with no change to how its firing.

 

Well, whoever had money in the office pool on "cracked cylinder head," you win.