indyhoya

Hi all-going back to the community for some help on a recent issue. 2001 XJ, ~220,000 miles. Was on a long road trip and on my last stop before coming home check engine light came on on the off-ramp and began running rough at idle and on the surface streets. Went to nearby parts store, code was P0301 Cylinder 1 Misfire. Spark plugs were overdue so swapped those out at a nearby parts store, reset the battery, still running rough with maybe a slight improvement. Spark plugs showed mostly normal ware, cylinder 1 had some burn marks and more gunk on the threads. Went back on highway to get home, once up to higher RPMs Jeep sounded fine like it always has and check engine light did not come back on. Upon getting home, again on off ramp the check engine light comes back on and is running rough. Today started looking for answers, took out the brand new spark plugs for compression test, all have good pressure (between 145 and 160) with exception of Cylinder 1 reading ~60 so definitely have a problem there. Spark plug in cylinder 1 has bent tip (see photo). These new spark plugs were gapped to .035 and were not damaged going in. But to confirm, after straightening back out and gapping but turning engine over, the same bend came back in the plug. Didn't see any foreign objects or anything that had broke off in the cylinder, fished around some with a coated wire and didn't feel anything either.

Next move will be removing valve cover and taking a look at the springs. I don't have much familiarity or experience with engine so hoping someone can point me in the right direction based on what I'm experiencing and what the right moves might be. I have never had any engine issues and to my knowledge the previous owner (purchased 6+ years ago) didn't either. That also means I haven't done any engine maintenance apart from spark plugs so if there are other suggested high mileage maintenance items I should do, assuming I can solve this issue that would be helpful too. Thank you!

awg

I would suspect your piston is damaged, and would insert a borescope down the spark plug hole before doing anything else

Dave51

I think you're destined to pull the head. Could also be a piece of valve floating around in there.

Could also try fishing around with a magnet (although make sure whatever gimmick you use is secure, lest you now have TWO foreign objects down there).

BlueRidgeMark

I agree with both awg and Dave. A borescope is cheap these days. 20 bucks on Amazon for a cheapo that works with your phone. I have one, and it's great.

RockyMtn96XJ

I'd take the borescope route as well. I've never looked into a borescope specifically, but I would guess your local auto parts store has one you could get on loan. Hopefully its a quality one and the image comes out good. Some of them even have magnetic heads, or has a "claw" on the end of them to help retrieve F.O. I remember plenty of times in my Air Force career as a young Airman having to work 12 hours, with the last 3-4 hours being with a borescope on top of an F-22 trying to find a dropped fastener somewhere down in a cavity of the jet. The magnetic ended borescope was a lifesaver.... more of a timesaver, but either way.

BlueRidgeMark

Here is the one I bought on
Here is an example of the picture quality.

bluejeep2001

I f you have all the same plugs in the other pistons and none are bent, make sure that plug is exactly the same. It sounds like your connecting rod bearings are bad in nbr 1 and allowing the piston to travel too far up in the hole. If it went up far enough to hit a plug it might have hit the valve, and it might have damaged the head gasket where the piston came higher than the deck. With the valve cover off and the piston at TDC, at least #1 is easy, see if you have excessive wobble in the rocker arms, the bent valve is the one thats really loose. A broken spring or valve retainer is also a possibility. If the valve bent far enough to hit the spark plug, you would have 0 compression so I assume the bad plug is due to the piston originally....good luck

indyhoya

Thanks everyone for the insight! I ordered a borescope and its supposed to come in by tomorrow so hopefully I will have some more substantial updates by the weekend.

I took the valve cover off today, overall things looked pretty good and no obvious issues seen in the springs or rockers. Photos are below. I did not check for excessive wobble at TDC but will check that out-thanks for pointing me in that direction, bluejeep. I did come across another thread on the forum referring to this service bulletin (http://wjjeeps.com/tsb/tsb_wj_0900303.pdf) which addresses exhaust valves being slow to close due to the valve not rotating properly. I did notice two faint straight lines on the valve stem tip for Cylinder 1 instead of the clear bulls-eye wear pattern on Cylinder 2. I plan to rotate the valve to address this but suspect its not the cause of my bent plug issue. Any other input in the mean time while I wait for the borescope to come in is appreciated.

tech

I would go ahead and remove the head , looking in the cylinder is not going to fix it . you need to take it apart to change what's going bad , you can look inside but to me it will be a waste of time . I think you have a piston problem and looking at it will not fix it .

indyhoya

Got the boroscope late today and took a quick look (photos below). Nothing obvious jumped out to me, there wasn't any foreign objects in there and everything appeared to be in tact. The scrapes and gouges on the piston shot I believe are marks in the carbon/soot from fishing around with an insulated copper wire to see if there was anything inside before getting the camera. There did appear to be a bit of a scrape/shiny edge on one portion of the intake valve. I'm going to try a few other things tomorrow with the piston at TDC, and try to see what position the plug is in when it's getting bent. As some have suggested the unavoidable move may be to remove the head. I've never done that before, any potential pitfalls or potential to cause damage to be aware of? So far this thread (https://www.cherokeeforum.com/f2/beg...ft-1-a-166226/ ) is the best guide I've come across but would be grateful if there are any other resources that you can point me to. Thanks again! ​​​​​​​

Dave51

Got an air compressor? Shoot air in the cylinder at TDC (makes no diff) then listen at the throttle body and exhaust pipe to see if there's a problem with the intake valve or the exhaust valve. Might help to determine which valve you should be looking at. If they don't leak, then it's rings.

Dave51

2000 SM. Can't hurt.

https://cdn.xjjeeps.com/pdf/en-us/20...ice-manual.pdf

Dave51

Is this something?

awg

my ole matey did mention the 4.0 had a couple of failure issue

* broken or shrunken piston skirts
* worn conrod end bearings

Idunno

Less than half of the required compression and a bent spark plug tells me a piece of broken valve is popping around in the cylinder and it's time for the head to come off.