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2001 Misfire cyl 3 with cracked spark plug, what could it be?

McMuffinStuffer

NAXJA Forum User
Location
Texas
Hi there, I'm new to the site.
I've been looking online for some time now trying to figure out how to fix my cherokee.
It's a 2001 2wd with 156k miles. About 3 weeks ago or so I got the P0303 Misfire code. My jeep drives generally just weaker, sometimes having to nearly step on the gas fully going on steeper roads.

I checked the coil pack and noticed the 3rd spark plug had a crack around the white area (i had changed the spark plugs early this year). So I replaced it and had no change.

Then a couple days later I replaced the coil pack for $140 but that also had no change. So after a couple days I returned it.

I'm not really sure what to do next or what could've caused the spark plug to crack. If you have any ideas or tips I'd be very happy to look into them and let you know how it goes. Thank you:worship:
 
A cracked insulator on a spark plug is usually due to overtightening on installation. It was one of the first mistakes I made when I got my first car. Since then, I start screwing the plugs in by hand as it is the best way to feel that they have engaged the threads properly. Then I finish off tightening with a torque wrench set to the lowest setting the head manufacturer recommends for the plugs.

From your description of weak performance, you probably have a cracked cylinder head. The 2000-2001 4.0L XJ were fitted with a cylinder head with casting number '0331'. A large number of them have developed cracks between cylinders 3 and 4. It's possible that a cracked head could cause additional stress in the head that could crack a plug but I'm not aware of it being reported as a common symptom.

My 2001 hasn't cracked yet, but I am keeping an eye out for a 2002+ coil on plug head from a TJ or WJ. Actually, my preference is for a complete engine from a 2004 WJ as the block is also stronger.

For a new replacement head, the Clearwater Head is probably the best value.
 
I just thought I would add that I know the WJ block is not interchangeable with an XJ block on a LHD XJ. However, my XJ is RHD. European WJs were designated WGs built in Austria. The RHD XJ blocks appear to have differences from the LHD blocks particularly in relation to the water pump, steering pump and A/C compressor location. I am willing to take a chance on acquiring a whole WG 4.0L primarily for it's head as I am guessing that the RHD market was too small for too many variations of the block.
 
Hey Vince, just to let you know I replaced my rhd engine with a lhd engine from a zj and it all bolted up. As far as I can tell all xj blocks are the same, you only get into the different boss castings after xjs were out of the picture.

Mcmuffin, Vince is probably right, check your oil I bet its milky and your head is cracked, and at this point your motor is ready for a rebuild with a new head.
 
If your 2000-2001 XJ Cherokee has a cracked 0331 head, buy a good used redesigned and more durable TUPY 0331 head from a 2002+ 4.0L TJ Wrangler or WJ Grand Cherokee.

XJ Cherokee and ZJ Grand Cherokee 4.0L engine blocks interchange. LHD or RHD should have no difference in the basic block structure.

2000+ TJ Wrangler and WJ Grand Cherokee 4.0L engine blocks interchange.

XJ/ZJ blocks, and the 2000+ TJ/WJ blocks DO NOT interchange without significant modifications.

TJ/WJ 4.0L Engine blocks underwent clean sheet design changes effective in the 1999 WJ Grand and 2000 TJ Wrangler. These blocks are not interchangeable with XJ/ZJ engine blocks. The reason is motor mount bolt holes and belt driven accessory mounting bolt holes are in different locations, or not present at all, TJ/WJ vs. XJ/ZJ.

Remove and re-use as needed or required from your original engine: Fuel Injector rail, Intake/Exhaust manifolds, flex plate/flywheel, cylinder head, distributor-less ignition or distributor assembly, engine sensors, motor mounts, fan belt driven accessories and/or mounting brackets.

XJ: "Regular" Cherokees 84-01
ZJ: Grand Cherokee 93-98 (Gen1)
WJ: Grand Cherokee 99-04 (Gen2)
 
Hi vince, thanks for the reply. I also wanted to note that I do have a leak of coolant which ive heard causes cracked heads. My jeep doesnt overheat though. I bought the jeep for $800 about 2 years ago. In this position would you recommend replacing the head and getting it fixed or selling the jeep? I dont have a lot of money but it is technically possible for me to come up a bit for repairs.
I love my jeep but I rather not spend so much in the long run.
 
I'm really not the best person to ask this question. I will spend every penny I have to get my Jeep running again and I have been divorced twice! My Jeeps are really important in my life. My gut feel is that you would be better off selling it. Don't fall into the trap of the sunk cost fallacy. In the past, I did it a lot. Watch this video.

If you already have experience of doing a cylinder head replacement and can get a good condition, used 'TUPY' head real cheap that doesn't need new valves/guides, then it is probably worth doing IF you are doing the work yourself. But there are risks that it could get more expensive as you start taking the engine apart. Like the condition of the water pump, replacement of which should also include the viscous fan clutch. Hoses, drive belt, engine mounts are all extra things that might need to be replaced.

A brand new replacement Clearwater head will cost about the same as what you have invested in your Jeep. Even with a good used head, at a minimum you will need a head gasket kit with new bolts, manifold gasket, rocker cover gasket, RTV, coolant, engine oil, oil filter, spark plugs. Most people undertaking this job will treat it as a major service and replace with new a lot of parts that have to be removed to do the job especially if the parts are old and have never been replaced before. It is awful when you have just done a major repair and another part has just failed that you missed an opportunity to replace while you had good access to it.

Some positives that you can take away is that:

1) You will consider very carefully a future purchase of a 2000-2001 4.0L XJ
2) You have a new opportunity to acquire a 4wd XJ
3) There are other Jeep models that you may like more than your XJ
 
Vince is on the money here. Unless you specifically WANT a 2wd, which is quite rare, you are looking at re-investing what you already have in it to repair it-maybe more. I would think in texas rust free earlier examples should be fairly plentiful
 
Suggesting selling the XJ or installing a Clearwater head is all rather premature, seeing as how the root cause of the symptoms has not been diagnosed.

It is possible that the symptoms are simply a faulty/damaged wire harness, a faulty OBD-II engine sensor, or another easy to repair issue.


Properly troubleshoot and diagnose the problem and then develop a budget and a plan for the solution. A well maintained XJ Cherokee with a 4.0L is capable of +300,000 miles of service.
 
Suggesting selling the XJ or installing a Clearwater head is all rather premature, seeing as how the root cause of the symptoms has not been diagnosed.

It is possible that the symptoms are simply a faulty/damaged wire harness, a faulty OBD-II engine sensor, or another easy to repair issue.


Properly troubleshoot and diagnose the problem and then develop a budget and a plan for the solution. A well maintained XJ Cherokee with a 4.0L is capable of +300,000 miles of service.
Well said
 
Properly troubleshoot and diagnose the problem and then develop a budget and a plan for the solution. A well maintained XJ Cherokee with a 4.0L is capable of +300,000 miles of service.


Very true. Establish the facts first. I shouldn't have jumped to conclusions so quickly just because it's a 2001. :twak:
 
Cracked head is directly checked if you don't have other symptoms using oil analysis. I've used Blackstone Labs several times as periodic checks. So far 200k on one of the jeeps (now sold) and no crack. 88k on the other and still good. (both 0331 castings)


I'm suspicious that cracks might be initiated by quick oil change places. Consider that the engine is hot, oil is drained, then the oil is replaced from a high-flow nozzle dumping the cold oil directly on the center of the head - where the cracks happen. Know also that oil-quenching is a metal tempering technique because oil takes a lot of energy to heat. Can't prove it but....



I think that misfire is pretty far away from cracked head as cause. There would be other indicators of cracked head first.
 
I'm suspicious that cracks might be initiated by quick oil change places. Consider that the engine is hot, oil is drained, then the oil is replaced from a high-flow nozzle dumping the cold oil directly on the center of the head - where the cracks happen. Know also that oil-quenching is a metal tempering technique because oil takes a lot of energy to heat. Can't prove it but....

Interesting theory, but very highly unlikely. The 0331 head has a design flaw or casting flaw that allows them crack. Often owner abuse and/or neglect of routine cooling system maintenance is a major factor in the failure.
 
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run the engine at night, open the hood and inspect in the dark for stray sparks. you may have more than one cracked plug! i had one cracked plug, crack very hard to see, but in the dark you can see the arcing spark easy. you may also hear a tic tic tic noise from a cracked plug, the noise the arc makes so check all six plugs!

run with a cracked plug for long, and the catalyst will be damaged, the engine brain will enrichen the mixture when it senses unburnt oxygen caused by the bad plug, the mixture is enrichend on all cylinders and the bad plug cylinder(s) will be sending raw fuel out the exhaust, very bad for cats.
 
Cracked head is directly checked if you don't have other symptoms using oil analysis. I've used Blackstone Labs several times as periodic checks. So far 200k on one of the jeeps (now sold) and no crack. 88k on the other and still good. (both 0331 castings)


I'm suspicious that cracks might be initiated by quick oil change places. Consider that the engine is hot, oil is drained, then the oil is replaced from a high-flow nozzle dumping the cold oil directly on the center of the head - where the cracks happen. Know also that oil-quenching is a metal tempering technique because oil takes a lot of energy to heat. Can't prove it but....



I think that misfire is pretty far away from cracked head as cause. There would be other indicators of cracked head first.

i dont think adding room temp oil to a hot head is going to harm the head the crack occurs over a coolant passage, coolant that might hit maybe 250F the oil quench from an oil change is not going to crack that head. The temperature difference is small. The cracked heads had a design or cast defect that the new heads fixed.
 
Consider that a head with the casting flaw in it isn't cracked initially. Thermal stress could aggravate it. Just a possible theory. Like a rock chip on a windshield - it could be the place where the crack initiates and travels.
 
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