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Unread 05-09-2013, 10:10 AM   #1
mntn-biker
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2000 XJ 4.0L P0300, P0303, P0304 & tuneup questions

We have a 2000 XJ 4.0L with ~160,000 miles and it is repeatedly throwing random P0300, P0303, & P0304 misfire codes. The heep seems to be running fine and starts fine. It just throws these codes and I clear them out and they come back. We bought the heep with 140,000 miles so not sure of when it had a tuneup so I figured I would start there since it could probably use it.

1. Give the throttle body a good cleaning.
2. Plugs & wires - what are good replacements for a stock 4.0L?
3. Is there a good coil rail I should get?

We will start with the above items but doing some reading, it sounds like it could also possibly be the crank position sensor. I am dreading having to replace that since it sounds like it will be a pain in the you know what to get at....

Your input is greatly appreciated!

Thanks in advance - Mike

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Unread 05-09-2013, 11:28 AM   #2
buildin1XJ
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Have or are you experiencing any unexplained coolant loss as you have the 0331 head casting which when it cracks it does so between #3 and 4 cylinders.
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Unread 05-09-2013, 12:35 PM   #3
mntn-biker
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Quote:
Originally Posted by buildin1XJ View Post
Have or are you experiencing any unexplained coolant loss as you have the 0331 head casting which when it cracks it does so between #3 and 4 cylinders.
I can't say that I notice any obvious coolant loss. I took a permanent marker and put a line on the overflow tank (cold) and will monitor it. Would there be any other noticable indications of a cracked head?
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Unread 05-09-2013, 12:57 PM   #4
buildin1XJ
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In my experience with the 0331 cracked head which are quiet a few you may or may not find coolant mixing with oil which will look like a chocolate milk shake, also look at your oil cap for the same. Also sometimes steam from the exhaust pipe. Most of the time it takes a while before you actually see the oil coolant mixture. The best advice I can give is to observe your coolant levels frequently. You may very well not have this problem as your codes may well be the result of bad sensors or coil packs, cam sensor, crank sensor, clogged injectors or even bad plugs. I would check into your coil packs and plugs first. while keeping a close eye on your coolant level.
You can find lots of info on the 0331 head crack issue by a Google search.
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Unread 05-09-2013, 02:08 PM   #5
79chiefs
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Get a compression, leak down test, and coolant tested for exhaust gases.
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Unread 05-09-2013, 02:32 PM   #6
buildin1XJ
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Please read the thread on here Cracked Head which has had a few posts to it today. Also read the link that TJ Walker posted to that thread. Many times compression tests will still fall within spec with a cracked head because by the time you get coil packs and plugs out the engine will not be hot enough to make confirmation. 2 other things to look at are the plugs if #3 or 4 plugs are cleaner than the others it could be because of coolant steam cleaning them. Also a coolant pressure test is another good way of testing.
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Unread 05-09-2013, 03:09 PM   #7
mntn-biker
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I think I will start with plugs 1st and check them for the above symptoms followed up by some plug wires if they all look the same color. Someone suggested going with Champion copper plugs gapped to .035?

After that, maybe the coil next? Someone suggested cleaning/rebuilding or new/rebuilt injectors? Maybe some Neon 703's? Then there are God only knows how many sensors....
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Unread 05-09-2013, 03:19 PM   #8
buildin1XJ
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If you have coil packs you do not have plug wires to replace.
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Unread 05-09-2013, 03:22 PM   #9
mntn-biker
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Quote:
Originally Posted by buildin1XJ View Post
If you have coil packs you do not have plug wires to replace.
Good point. Was thinking of my son's '97.... So plugs, then perhaps the coil (assuming the entire rail gets replaced???). I saw a coil rail assy for ~$100 at Advance Auto Parts.
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Unread 05-09-2013, 06:55 PM   #10
79chiefs
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Quote:
Originally Posted by mntn-biker View Post
Good point. Was thinking of my son's '97.... So plugs, then perhaps the coil (assuming the entire rail gets replaced???). I saw a coil rail assy for ~$100 at Advance Auto Parts.
I would do tests before throwing parts at it to please the jeep gods. This is as common as the 00-01XJ's because their HEAD is the problem. The tests will show you IF the head is the problem, and if not then you can search for the part that is the problem. It will save you money in the long run. just my 2cents to help keep your wallet from being stolen at the parts store.
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Unread 05-09-2013, 08:41 PM   #11
buildin1XJ
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The only reason I brought up the 0331 head issue was because it relates to code 303 &304 cyl. 3 & 4 however you do have a code 301. In my experience with cracked heads they normally do not throw codes due to a cracked head until it is really bad, the 303 and 304 codes could be a sign of a shared coil but the 301 coming along with the other codes becomes a little more confusing maybe a bad connection at the coil packs. Look at plugs, check the coil pack, cam sensor, and crank sensor. I am not saying to ignore coolant level at all. Keep us up to date on what you come up with. When dealing with a situation such as yours I like to use a systemic approach but at the same time keep a open mind set. Good Luck Man
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Unread 05-09-2013, 09:06 PM   #12
79chiefs
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Quote:
Originally Posted by buildin1XJ View Post
The only reason I brought up the 0331 head issue was because it relates to code 303 &304 cyl. 3 & 4 however you do have a code 301. In my experience with cracked heads they normally do not throw codes due to a cracked head until it is really bad, the 303 and 304 codes could be a sign of a shared coil but the 301 coming along with the other codes becomes a little more confusing maybe a bad connection at the coil packs. Look at plugs, check the coil pack, cam sensor, and crank sensor. I am not saying to ignore coolant level at all. Keep us up to date on what you come up with. When dealing with a situation such as yours I like to use a systemic approach but at the same time keep a open mind set. Good Luck Man
he dont have p01301, it is p0300, which is multiple, that goes along with the 2 p0303, and 0304, so cracked head is a very good possibility.
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Unread 05-09-2013, 09:25 PM   #13
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Well, I don't see the steam from the exhaust, I don't see the chocolate milkshake under the oil cap, and it doesn't seem to be low on fluid. I think I will throw some new Champion or Autolite OE copper plugs gapped at .035" in it and may just bite the bullet and throw a new coil rail on it all for ~$100 at my local Advance Auto Parts since I have it apart. With 160,000 miles, IMHO it's due for this and it's probably just a matter of time before the coil needs replacing anyway.

FYI - I am getting the P0300, P0303, & the P0304 codes.

Where do I find the 0331 casting number on the head? Just want to verify that is what I have on it and it hasn't been replaced with a different model year head already since we bought this with 140,000 miles and the service history is a complete mystery.

So if I do need to replace the head with a reman, do I get the same 0331 head and will this replacement head have the same issue? I'm guessing the heads cracking are due to a design flaw or poor quality casting material so what makes a reman head any better if it is the same base casting?

Then I have to ask the question, do I spend $400 for a head for an engine that has 160k miles on it or do we bite the big bullet and put an entire new reman engine in it instead? I see Marshall has 1 for $1600 including the head. Just sayin' since the rear main seal has a pretty good leak too and I heard that is a $700 bill to have it fixed in a shop. Between the cost of the head and the bill to have the rear main seal fixed, seems like it is almost worth just pulling the trigger on the reman motor if this head is cracked...
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Unread 05-09-2013, 10:06 PM   #14
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Sorry for some reason I had it in my mind you had a 301 instead of the 300 multi cyl. misfire. 303 and 304 go along with the #3 & 4 cylinders which narrows that down to either the cracked head issue or the coil pack as 3 &4 do share that coil. I suggest renting a coolant system pressure gauge from a place like A Zone then pressure up to around 5 PSI look through the oil cap hole and watch for coolant if you do not see it then remove the rocker arm cover and try again.
You will find on most 2000 models a aluminum fabric heat shield under the fuel rail carefully remove it and you will find the head casting # wright along side the rocker arm cover.
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Unread 05-09-2013, 10:19 PM   #15
buildin1XJ
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If you are going to be paying for replacement head + labor and an outrageous fee of 700 for rear main seal I would go with the reman. engine as long as it has an upgraded head such as a TUPY or Clearwater head.
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