Wojtas

Hey guys, my 01 xj with 134xxx miles on it has the check engine light on, with the description of a bad o2 sensor and a misfire in cylinder 6. Am I having cat fever here, too much back pressure or what? Should I run seafoam throught it and see if its a sticky valve, are the valves not rotating? Or is it the coil pack? Any help would be greatly appreciated guys, the check engine light dosent come on unless I really step on it.

Click-Click-Pull

Check the plug...what does the plug in No. 6 look like?

tjwalker

Yup, simple stuff first. I'd recommend you replace that plug at minimum; replace all of them if it's been more than 30k. Plugs can have tiny cracks in the insulator that are sometimes missed with a visual inspection.

Swapping of fuel injectors is also another thing to consider if plug checks out. If the misfire follows with the swap, you know what to do.

What are the exact codes? Be sure to address all of them. When you have multiple codes, don't assume that they are not related. They might not be, but oftentimes they are, sometimes in ways that we can' initially understand.

Wojtas

Alright, I will get around to checking the plugs tomorrow

I went to autozone, they hooked up their scanner and got the codes P0158 and P0306

P0158 read that it was a bad oxygen sensor in bank 2 sensor 2 (had to get the god damn jeep that has 4 oxygen sensors... great)

P0306 read that there was a misfire in cylinder 6 with possible causes including:
1. Ignition system fault-spark plugs
2. ignition wires
3. coil
4. vacuum leak
5. injector fault
6. high or low fuel pressure

Alright, if its the plugs or wires that an easy fix for me, an injector is do-able, coil too. I doubt its a vacuum leak or low or high fuel pressure... I just really hope its something as simple as my plugs

Now, this is where the oxygen sensor has me thinking, if the oxygen sensor is bad, could it be the cause of the misfire? I am planning on replacing the oxygen sensor ASAP so I can get rid of it from the list of **** that wrong with this turd

My burning question is, has anybody had this same problem before? If so, what was it? plugs, coil, sensors? I just don't want to buy parts that I don't need, and god forbid taking it to a shop! I'm a 17 year old that makes $8 an hour, I cant exactly afford a trip to the mechanic; ****, i can barely afford gas for this guzzler.

Any help would be appreciated guys, I will get back to you after I get a new O2 sensor on this bad-boy and check the plugs

Turbo X_J

If you have an '01 with plug wires, it's not an '01. Bite the bullet and replace the 4 O2 sensors now, they are a maintenance item.

Wojtas

Turbo XJ, you're right, no wires... just realized what I wrote after I wrote it... but hell, couldn't it be the spark plugs? I rather change all the plugs and hope that it solves the issue than get 4 new O2 sensors at $70 each...

JackJare9455

i agree to replace o2 sensors as they are a maintenance item... a rich condition can throw the voltage signal to an o2 sensor off and trip a code.. and the miss-fire could have that effect.

If it was me diagnosing.. I would think its a possibility that the miss-firing cylinder COULD cause the o2 sensor to miss-read.. but I don't believe the post catalytic converter sensor would cause the miss-fire..

SO.... try and fix the miss-fire first.. how are you at diagnosing spark? Have you tested spark before? If not.. it may be easier for you to just go down to the parts house and grab a 2 dollar auto-lite plug and toss it in there to see if that corrects it...

I am ANTI "parts chunking" to fix problems.. but a 2 dollar plug is pocket change if your going to pull it regardless and not quite sure of what you are looking at..

Check the wire going to the number 6 as well... do you have a multimeter? have you ever tested for resistance? (ohms)

look for cracks in the boot.. start the engine in the dark and give it throttle.. see if you notice any arcing around the head..

let us know what you come up with!

Turbo X_J

Yep, but if you do the O2 sensors now you'll be good for another 134k. Btw NTK O2 sensors (OE) on Rock auto are ~ $30 each.

Roler

This is useless to ask. What the cause is with somebody's symptoms/misfire, might not be yours. The causes that are in your list, could ALL be causing your issue. Maybe even have simultaneous things going on.
So, reading up on this and start checking, will narrow things down.
checking for spark, checking fuel pressure and checking for vacuum leaks or even leak down tests, are free (rental of equipment can be done at autopart stores in the US, we don't even have that luxury here). testing those will give you a lot of information from which you can go further.
Plugs are the next cheap first step.Then clear the code and see what comes back. Then come back here and we go from there.

IMO this, for you, is the most cost effective way of trying to solve the problem.

Dumajones

Change the plug's first ,, The 2000,2001 jeep Cherokees came from the factory with NGK ,,,(OEM Part # SP000ZFR5N)... (NGK part # ZFR5N). My 2000 runs better with NGK other then Champs, my 96 loves champ's.

JackJare9455

didnt even notice the year.. ignition coil "rail".. my bad..

Wojtas

Changed all 6 plugs, poured seafoam in the intake to clean out the injectors and all the nice gunk that likes to build up inside, engine seems to idle smoother and isn't having the same jerking issue it did when the misfire was present.

As for the oxygen sensors... they are works of satan himself. It is pretty clear to me that they have never been replaced. Tried an adjustable wrench first, when that didn't work I went to autozone and rented a oxygen senor socket, that still didn't work. I PB blasted the crap out of it and still nothing. The way these damn oxygen sensors are placed make it impossible to get any leverage. Is there any other tool out there? I would like to know if there is another method to do this before I am forced to take off the header pipes just to change the oxygen sensor.

As for the codes, I am not sure what they are saying after the plug change since I didn't get the chance to ask for a diagnosis at autozone.

My main concern now is getting these sensors off... any advice would be wonderful.

kjc

You might try loosening them when the engine is hot... or use a propane torch to heat up the bungs. Put a box end wrench on it (hex is best) and hit it with a hammer.

123danno

That said I had a 97 JGC with the same codes. I solved the misfire with a spark plug replacement with Champion Plugs. The O 2 sensor was replaced and did not fix the problem. That problem was a Cat. Conv. that had about half the core left. I checked that simply by hitting it with my fist and it rattled noticeably. I replaced the Cat and that fixed the O2 sensor problem. I agree with the above because every case is different.
I had the P0158 code on my 2001 JGC and I decided I wanted to clean the whole system before I started wasting money and time on replacing 4 O2 sensors. I used Cataclean which has many good reviews (look it up) and some dissatisfied customers. It did turn off my check engine light while it was at full strength in my system. But after filling up and burning 10 gallons of fuel the code P0158 came up again. I did notice a boost in MPG of 3 miles per gallon. So it was a lose win for me.

123danno

I don't want to highjack this thread but since you note P0158 as a problem I have a little experience with it. I have this problem now, P0158, and this is going to be my very economical approach. First clean the system with Cataclean, as noted.
Does anyone know how to test whether your engine will just no longer operate to the government standards. That would save a lot of money.

This approach is just starting to throw money at it. Get under the jeep and hit the cat. with my fist to see if that is rattling if so replace it.
If not, testing starts at the Bank 2 Sensor 2 with this as a guide. (very informative)

http://mr2.com/TEXT/O2_Sensor.html

It sucks but take some time to learn how it works and how to test it.

Proceed accordingly. If the O2 sensor has failed, replace.
If it's not bad this is where I am at a loss. I might test all the others and proceed accordingly.
Figuring it out as I try to save my money.