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Thread: '04 TJ 4.0L Spark plug specifics

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    Smile '04 TJ 4.0L Spark plug specifics

    Ok, problem is in my 04 tj I have a set of plugs that I decided to swap out and give my baby a tune up. In removing the old plugs and hitting the auto parts store I got home and compared what was in there to what the parts store had given me. The new set measured over 1/4" longer from thread to til thank the plugs that were in it. I called a few other parts stores hoping what I was given is incorrect, but all stores had same parts numbers and cross references were all that length. Not one was the 1/4" shorter. So I didn't use them . I ended up just getting the exact plugs that were in it only a new (which I might add only referenced back to use in a SAAB motor) . My question is " is there anyway to 100% figure out what has gone on here? Or is there a number on the head casting somewhere I can reference? Also my jeep is a little sluggish for only having 150k on it, could this be partially because of these plugs? I assume that each plug is designed specifically for each combustion chamber and at a specific temperature. Any info anyone has would be appreciated. I just did not want to put a longer plug in and have it hit anything and cause me problems. Thanks in advance

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    Stickybongsmoking is offline Yes, this is gawd damn muthafockling CTD NUT.
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    Assuming you have the factory engine and head, I would be going with the plugs that the several listings you verified, all specified. The fact that the plugs you have installed now do not match any of the listings would preclude most anyone into thinking that the currently installed plugs are incorrect.

    It is possible that a previous owner may have decided that the engine needed a different heat range plug for some reason. Many people do not understand what the heat range of the plug means and make assumptions. If we can assume the engine you have is stock with stock deck height, head thickness and pistons, then it is reasonable to expect the compression ratio is at, or below, stock. Therefore, the OEM spec'd plug should be used.

    The plugs you have that are shorter are for a colder than OEM spec'd heat range. Why anyone would do that on a stock engine and not use the OEM spec'd plug, I have no idea.
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    Go grab plugs that are specified for your engine. If the plugs you purchased are the correct ones and the ones that were in there are specified for a different vehicle I think, as a reasonable person, you can assume the previous owner put the wrong plugs in. People are notoriously cheap and someone probably thought "well these ones are on sale why can't I use them" and slapped the wrong set in there.

    Use what is spec'd for your vehicle. Go to Napa and tell them you have an 04' TJ 4.0L and need plugs. Napa is better than CTC and will get you what you need. I don't use anything fancy in my jeep. Straight up Champion copper plus for mine.
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    Go to the dealer and get a set of plugs from them. That way you know you are getting the right plugs for your year of jeep.
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    ....and from what I have seen....nothing fancy is required. OEM spec is sufficient
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    The stock plugs for the 04 jeep TJ with a 4.0 engine are NGK P/N ZFR5N stock #3459. It will be stated on the emission label under the hood if it's still there. It is also stated in the FSM. Parts places regonize the stock number. If i remember they are about $3.50 a plug, after market or at the dealer.

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    Quote Originally Posted by nmj48 View Post
    The stock plugs for the 04 jeep TJ with a 4.0 engine are NGK P/N ZFR5N stock #3459. It will be stated on the emission label under the hood if it's still there. It is also stated in the FSM. Parts places regonize the stock number. If i remember they are about $3.50 a plug, after market or at the dealer.
    We always used Champion Copper Plus when I worked at the dealership!

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    OK all in all i am going to take of the coil rail, take #1 plug out and install the new ideal suggested plug and turn over the engine then remove the plug to confirm that it hasnt been hit or touched by piston. if its clear i am going to change them all. Thanks everyone for your help. Nice to be a part of a group of helpful people. Happy wheeling folks, ill let ya know how it goes this week.

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    Quote Originally Posted by JeepFreak1 View Post
    OK all in all i am going to take of the coil rail, take #1 plug out and install the new ideal suggested plug and turn over the engine then remove the plug to confirm that it hasnt been hit or touched by piston. if its clear i am going to change them all. Thanks everyone for your help. Nice to be a part of a group of helpful people. Happy wheeling folks, ill let ya know how it goes this week.
    It's not going to hit the piston if it's the plug that is factory recommended for the vehicle.

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    i know this is for xj's but they are basically the same for all 4.0L
    older 4.0L need a heat range of 9. nothing fancy, just champions. the later 4.0L is a 12 for heat range. again, don't get fancy plugs, they don't like them.


    left is renix plug FR5 then middle is H.O plug FR5-1 and the upgradable plug the FR5GP on the right.
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