HOW TO: Change Spark-Plugs

[67Customs]

Just a reminder to everyone. It is important that plugs are changed per recommended schedule (every 30K), particularly when replacing the original plug (which are obviously the least expensive plugs money can buy). I observed on my KJ that at 30K the plug tip erosion was approx. +0.015'-0.020". I would think another 15-20K miles would have resulted in excessive plug tip erosion to result in potential engine misfire which could lead to some other (bigger) problems (e.g. catalyst overheat).

I changed mine at 30k on the dot and I had one that was almost touching and one more that were almost the same. The other's were close to fine.

 

[belvedere]

I changed mine at 30k on the dot and I had one that was almost touching and one more that were almost the same. The other's were close to fine.

Could you clarify? What was almost touching?

 

[67Customs]

Could you clarify? What was almost touching?

I'm sorry.

The tip was almost touching the electrode. The gap between them had almost completely collapsed.

 

[belvedere]

I'm sorry.

The tip was almost touching the electrode. The gap between them had almost completely collapsed.

Strange...not sure how that happened, unless deposits built up between the two. Does it look like that's what happened?

 

[67Customs]

Strange...not sure how that happened, unless deposits built up between the two. Does it look like that's what happened?

No, the tip was bent towards the elctrode. It looked like JJs on the first page of this thread as far as build-up goes, the tip was just bent. Everything looked normal other than that. They looked pretty good otherwise.

I assumed this was "normal" gap wear/errosion from old crappy sprak plugs. The motor ran great before and after the change, so it didn't alarm me.

 

[Dave]

No, the tip was bent towards the elctrode. It looked like JJs on the first page of this thread as far as build-up goes, the tip was just bent. Everything looked normal other than that. They looked pretty good otherwise.

I assumed this was "normal" gap wear/errosion from old crappy sprak plugs. The motor ran great before and after the change, so it didn't alarm me.

If the tip was bent toward the electrode, then maybe someone put them in like that before you bought your jeep?? All the plugs I ever pulled always had the gaps spread from wear. It is good that you got those out anyway. When I get new ones I even check the gap before install.

Dave

 

[belvedere]

When I get new ones I even check the gap before install.

Dave

Same here, and they usually need adjustment. I have to say, though, that the NGKs I just installed were right on. I've had good results with NGKs in everything that I've tried them in.

 

[67Customs]

If the tip was bent toward the electrode, then maybe someone put them in like that before you bought your jeep?? All the plugs I ever pulled always had the gaps spread from wear. It is good that you got those out anyway. When I get new ones I even check the gap before install.

Dave

That is completely possible, but unlikely. I checked the service history on it before buying it and it never went in for a spark plug change. The owners took care of it, but most everything was done at the dealer. It is possible that the PO's changed them, but I got it at 15k miles, so I really doubt they were changed before I bought it.

I could have happened from the factory.

 

[blue_kjR417]

i just changed mine, i used the autolite platinums as well I didn't have much trouble at all. I got done in under an hour now I'm about to go fire her up and see how she purrs

 

[jas32]

That is completely possible, but unlikely. I checked the service history on it before buying it and it never went in for a spark plug change. The owners took care of it, but most everything was done at the dealer. It is possible that the PO's changed them, but I got it at 15k miles, so I really doubt they were changed before I bought it.

I could have happened from the factory.

It's impossible for a plug gap to become smaller in use, that is why spark plug engineers use the term "erosion" since the spark eats up a small piece of the tip every time it fires. The only logical explanation is that someone probably drop the plug just before it was installed. Quite unlikely to happen at the engine assembly plant since if someone drops the plug they will most likely get a new one next to them instead of picking it up from the floor.

 

[tjkj2002]

It's impossible for a plug gap to become smaller in use, that is why spark plug engineers use the term "erosion" since the spark eats up a small piece of the tip every time it fires. The only logical explanation is that someone probably drop the plug just before it was installed. Quite unlikely to happen at the engine assembly plant since if someone drops the plug they will most likely get a new one next to them instead of picking it up from the floor.

Actually the plug gap can shrink while in use without being dropped before hand.

 

[tjkj2002]

When the gnomes hit the plug with their little hammer from within the combustion chamber?

No but can happen at high rpm's in a very lean condition.

 

[67Customs]

It's impossible for a plug gap to become smaller in use, that is why spark plug engineers use the term "erosion" since the spark eats up a small piece of the tip every time it fires. The only logical explanation is that someone probably drop the plug just before it was installed. Quite unlikely to happen at the engine assembly plant since if someone drops the plug they will most likely get a new one next to them instead of picking it up from the floor.

All I know is this...

1) I am very possitive they are factory plugs.
a) They are the factory spec plugs.
b) I pulled service records for the Jeep. The Jeep was purchased at my local dealer and serviced at my local dealer. Not one item on that list pertained to changing of plugs.
c) I purchased the vehicle @ 15K miles. Rarely do normal car owners change plugs before that and if they do, they usually don't go back to factory plugs. For something to have been wrong with the motor big enough for them to have had to have changed the plugs, I would have seen it on the log. The motor has ran perfect for me since I got it, so I highly doubt something was in the motor big enough to bend them.

2) When I pulled the plugs out, three of them had gaps smaller than factory. One was very bad.

3) It is apparently possible that plug gaps can shrink. Especially on really crappy plugs. Unless they were done that way from the factory (which you said yourself was highly unlikely), it had to have been done internally and since the motor has been "sealed up" since it was made and nothing has ever been wrong with it, it isn't likely that something was bouncing around in there.

 

[Dave]

All I know is this...

1) I am very possitive they are factory plugs.
a) They are the factory spec plugs.
b) I pulled service records for the Jeep. The Jeep was purchased at my local dealer and serviced at my local dealer. Not one item on that list pertained to changing of plugs.
c) I purchased the vehicle @ 15K miles. Rarely do normal car owners change plugs before that and if they do, they usually don't go back to factory plugs. For something to have been wrong with the motor big enough for them to have had to have changed the plugs, I would have seen it on the log. The motor has ran perfect for me since I got it, so I highly doubt something was in the motor big enough to bend them.

2) When I pulled the plugs out, three of them had gaps smaller than factory. One was very bad.

3) It is apparently possible that plug gaps can shrink. Especially on really crappy plugs. Unless they were done that way from the factory (which you said yourself was highly unlikely), it had to have been done internally and since the motor has been "sealed up" since it was made and nothing has ever been wrong with it, it isn't likely that something was bouncing around in there.

67customs......did you notice a big improvement in performance and fuel economy when you changed them out with properly gapped ones?

Dave

 

[67Customs]

67customs......did you notice a big improvement in performance and fuel economy when you changed them out with properly gapped ones?

Dave

No, I didn't notice a big improvement but did notice some improvement. Less than I though after seeing what I pulled out, but improvement none the less.

I gained an average of ~ one mile per gallon (0.8 improvement according to the EVIC).

I didn't feel any power difference in normal driving conditions, however, she struggles less when pulling my camper than she did before when pulling hills at higher RPMs. So, I did gain some power back in that rpm range.

I guess you could consider that big improvement just for changing out spark plusg, though.

 

[desertkj]

It could also be that either the Jeep or the spark plugs were assembled on a Friday and did not exactly meet spec, but were shipped anyways. If that never happened, there would be no need for a warranty right?

 

[The Fixer]

I swapped the original plugs (7 years old, 32K miles on them) on my wife's KJ yesterday. Indeed, the color was decent, but the gaps were way off (some were out over .050!!) and the electrodes almost looked like they were cut on an angle. It was definitely time to replace them!

As far as getting the #6 plug out, I moved the coolant tank (remove 2 10mm nuts, easy with a deep socket) up and almost on top of the cowl, then was able to reach underneath the coolant tank and remove the #6 plug with just a straight 8" extension on my ratchet - no swivel joint necessary.

 

[jnaut]

No, I didn't notice a big improvement but did notice some improvement. Less than I though after seeing what I pulled out, but improvement none the less.

I gained an average of ~ one mile per gallon (0.8 improvement according to the EVIC).

I didn't feel any power difference in normal driving conditions, however, she struggles less when pulling my camper than she did before when pulling hills at higher RPMs. So, I did gain some power back in that rpm range.

I guess you could consider that big improvement just for changing out spark plusg, though.

Yeah, I guess depends on how you define 'big'. That sounds about right on the performance gains for switching plugs. I've got a thread here somewhere where I posted photos of my plugs-- they were pretty worn. Idle smoothed out, anecdotal increase in gas mileage (don't have an evic, so I can only measure once per tank) and she seemed more responsive. Ultimately, I think the 3.7 is a pretty resilient engine and runs fairly well on crap plugs. That's just my opinion.

 

[jnaut]

As far as getting the #6 plug out, I moved the coolant tank (remove 2 10mm nuts, easy with a deep socket) up and almost on top of the cowl, then was able to reach underneath the coolant tank and remove the #6 plug with just a straight 8" extension on my ratchet - no swivel joint necessary.

I mean to say something about this when I did my plugs and I think it's important.

You can get your #6 plug out without removing the tank, it just requires a couple of extenders and a swivel. I did remove my intake hose which only takes about 1 minute. Plus it lets you inspect the throttle body for dirt and what not. Basically the setup from the bottom up was: Socket/8" extender/Swivel joint/6" extender/wrench. A little Rube Goldberg, but it worked really well. It did require a little support with my left hand on the 8" extender, to keep it from wobbling from side to side. Didn't have to put any pressure on it, just use your hand as a guide.

 

[The Fixer]

I mean to say something about this when I did my plugs and I think it's important.

You can get your #6 plug out without removing the tank, it just requires a couple of extenders and a swivel. I did remove my intake hose which only takes about 1 minute. Plus it lets you inspect the throttle body for dirt and what not. Basically the setup from the bottom up was: Socket/8" extender/Swivel joint/6" extender/wrench. A little Rube Goldberg, but it worked really well. It did require a little support with my left hand on the 8" extender, to keep it from wobbling from side to side. Didn't have to put any pressure on it, just use your hand as a guide.

I tried it that way first, the only problem is that I've never changed the plugs in the 7 years we've owned it, so they were pretty well "stuck" in there. The first five plugs all needed some leverage so I was worried about breaking the swivel joint. The new ones went in smooth as silk with the anti-seize on them, but the old ones came out with lots of crud on the threads. I guess I should have changed them a few years ago, but it's got such low mileage that I didn't bother.