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How to change Spark Plugs on a 2004 TB with 4.2l

75K views 105 replies 63 participants last post by  xxomegawpnxx 
#1 ·
Hello

I wrote a HOW-TO on changing spark plugs. I took pictures while I did this as well. It looks like I cannot upload the pictures or Word Document until I post more. I tend not to post much as I find everything using 'Search'. So here is the text of the article I wrote. If anyone wants the actual word document with pictures send me a PM with your email address.


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So you want to change your spark plugs in your Trailblazer/Envoy with the 4.2L 6? I have a 2004 Trailblazer EXT 4X4 with the 4.2L 6 and did this a while ago. This is a very simple job that took me about 2 hours because I decided to snap some pictures. I will outline the steps I went through. I make no warranties regarding these instructions, I am merely offering up my notes as to how I did it. The tools needed are a straight blade screwdriver, 5/8 Spark Plug socket, 10mm and 13mm sockets, extensions and ratchet, anti-seize and new plugs.

The first step is to remove the Air Resonator and intake tube. There are two hose clamps, one on each side of the resonator that you remove. There are held on with clamps that use a straight blade screw driver. Once the hose clamps are removed you need to pull the hose off the resonator that goes to the air filter. Next there are two 13mm bolts on the passenger side that hold the resonator to the valve cover. Remove these. Next lift up the resonator from the passenger side and then pull the resonator off the throttle body. Store this, the clamps and bolts for reassembly.

Now you will have ready access to the coil packs and plugs. Each coil pack is held on with a 10mm bolt. I did one at a time to make life easy. Unscrew the 10mm bolt from the coil pack. I took a small straight blade screwdriver and pried up on the coil pack. Once the pack is loose I pulled it up and set it to the side. There is enough wiring that you can easily do this. Next use a 5/8 spark plug wrench and remove the plug. Use care that nothing falls into the spark plug hole. I put a little anti-seize on each of the plugs so removal will not be so hard next time. I gently tightened them down. If you prefer to use a torque wrench you would need to look up the specs.


Here is a shot of the coil pack pulled out of the way to gain access to the plug.


Here is my finished product, topped off with a K&N Cold Air intake. When I did this I ended up installing Bosch Platinum +4 plugs. The only reason is that is all I could find. I would have preferred Nippon Denso Iridium’s but they were not available. After the new plugs and K&N (My TB had 45,000 miles when I did this) I took a trip to Florida. I had a cargo topper on, 3 kids and my wife and I. I averaged 75MPH the entire trip and 19.5MPG. This is a marked improvement from where I started. Around the city it is averaging 15. While not stellar mileage, it is better. As for power it is really hard to say. I tow a 4,800lb RV trailer with the TB and the first trip is coming up soon. I am anxious to see if this helps. I was contemplating trying a TB spacer from Air-Raid as this is supposed to help low speed performance. I am very skeptical of things like that but if I can find one on eBay cheap enough I may just try.

If there is enough interest in this article I also did brakes on all 4 wheels. I may write that up as well. Thanks and hope this helps someone out.

I the moderator wants the Word document shoot me a pm and let me know how to post it.

Keith
 
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#2 ·
good post..but don't bother with the tb spacer..majority say it is not worth the money...also when do you recommend changing the sparkplugs..i have an 04 with 30k but i bought it used
 
#3 · (Edited)
good post..but don't bother with the tb spacer..majority say it is not worth the money...also when do you recommend changing the sparkplugs..i have an 04 with 30k but i bought it used
:iagree:
The owners manual of my 05 states to replace the plugs at 100K. I have heard of others of this forum who have done so at that mileage.
FWIW many have had problems with the Bosch Platinum +4 plugs on these engines. The OEM Delcos are the recommended ones when it's time to replace them.

http://forums.trailvoy.com/showthread.php?t=21855
 
#4 ·
u can wait till 100,000 if its operating properly.

I changed mine at 100,000.
I noticed no performance difference. no 'significant' difference. I mean it worked fine before.
the used ones looked used of course, but didnt look to be in terrible shape. I changed simply because they reached 100K.
I did use the new Iridium tipped AC delcos
if you dont feel comfy, maybe 75K?
 
#6 ·
I have heard horror stories about plugs seizing or galling in aluminum heads. I always use a small amount of never-seize on threads of replacement plugs - especially if they're likely to stay in place for 50,000+ miles. I am careful not to put so much never-seize on that it might foul the (gap).
 
#7 ·
Yeah, I have heard the opposite. I was told to always use a bit of antiseize on the threads of sparkplugs. Especially with aluminum heads. I do with my Lincoln, which I change the plugs on about once a year (probably unnecessary but I use copper plugs and its easy as hell to do). Are the heads on TB's aluminum BTW?
 
#45 ·
Yes, the 4.2L has an aluminum head. As well as the 5.3 I believe. The 4.2 is a lost foam cast aluminum block also, ever wondered why if you take a close look at your block, it resembles styrofoam? Cause thats what it started out as:)
 
#9 ·
I have the same question about anti-seize on the plugs.
I have always heard/believed that with aluminum heads it is a good idea to use it, however the local dealer service dude told me "GM does not recommend using it".

I replaced my plugs @ 100k and there was not any evidence that it was used originally but of course it might have cooked off long ago.

So still a dilemma ... to seize or anti-seize?

BTW the old plugs were in surprisingly good shape and I could not tell a difference in performance after the change + throttle body cleaning.

I am very interested in the truth/facts about the anti-seize. I worry that I may have created a future problem by not using it.

Thanks
 
#10 ·
Re: the 10mm bolts that hold down the covers over the spark plug hole. Make sure the engine is cold before removing these bolts. Some have had them break off in the head while trying to remove them from a warm or hot engine. They are fairly long and thin, so it does not take much to wring them off.:nono:
 
#14 ·
I did it! I took my stock plugs out at about 50k. check them and put anti-seize on the threads and put them back in, just cause I read about guys breaking them off and have thread damage after pulling them out at 100k or so, any time you can prevent something costly why not do it.
key is not to put so much that its going to cause a problem, just enough to make your job easier when that time comes.

everyone does what they want to there trucks, just cause GM cause to do or not something doesnt mean its going to hurt anything.
 
#15 ·
plugs

I haven't changed my plugs on the T.B. yet, but on my 00 truck I changed them at 68,000 because on some truck sites they where talking about getting them out of the head was a problem, when I pulled the plugs they had anti-seize on the original plugs from the factory, so I used a dab of anti-seize on the new iradium plugs also.:cool:
 
#16 ·
Now that I have enough posts to publish the pictures here you go.

I have a few comments as well, I installed the Bosch Platinum +4's. They seem to work OK but personally I do not like them. I am going to swap them with a set of Nippondenso irdium plugs. I know the manual says change them every 100K but my problem is I plan to keep this vehicle a long time. I do not want to have to worry about removing the plugs from the aluminum head after that long. I guess you can call it cheap insurance.

Keith
 

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#19 ·
...I installed the Bosch Platinum +4's. They seem to work OK but personally I do not like them. I am going to swap them with a set of Nippondenso irdium plugs.
What is it that you don't like about the Bosch plugs??? I have tens of thousands of miles in several vehicles with them and never had a problem... In fact, I'm currently in the middle of a cross country road trip and posting from a hotel room in Santa Rosa, NM... I filled up just inside of NM and 65 miles into the tank I'm showing 24.5 mpg average economy with my 3.73 geared 4x4, 67 mph and A/C on the nearly flat lands of I40...

Now I know the plugs aren't gaining me anything mileage wise, but they certainly ain't hurting performance...
 
#17 ·
thanks. this should help others on here.
I changed my plugs at 100,000.
I used a breaker bar to easily turn the plugs....
where they stuck? I dont know.
I didnt want to be leaning over the engine trying to loosen the plugs with a normal sized ratchet.... so I used a breaker bar and just easily turned the plugs. they came right out. I didnt see any signs of them being seized or anything.
 
#20 ·
On my '06 I changed the plugs at 53K, and replaced with the 41-103's. I could tell right away a small improvement in pep - seat of the pants. Mileage on a 300 mile trip was up .5 mpg. The only trouble I encountered was the plug socket has a rubber insert to hold the plug, and my socket was old, so when I replace the next to last plug (naturally) the rubber insert stayed with the plug, and I didn't see it. I felt a resistance with I tried to connect the coil wire, so I felt around in the hole and determined what happened. I used anti-seize (as always) and the dielectric grease inside the plug wire. Thanks to everyone on the pictures, info and the change in the AC plug number. I definitely suggest changing them before 100,000.
 
#28 ·
Consider a slightly different take on this advice. My advice is to remove them on a hot engine. But don't install them until the engine is totally cold.

Here's my logic. The coefficients of linear expansion are not the same for steel and aluminum. They are:

Steel 11.0 to ~13.0, depending on the composition

Aluminum 23.0

http://en.wikipedia.org/wiki/Coefficient_of_thermal_expansion

As you can see, for a given increase in temperature, aluminum expands about twice as much as steel. So, if the engine is hot, the aluminum will have expanded more than the steel spark plug, so it should come out easier.

For installation, however, if you put a cold steel plug into a hot aluminum engine, you will be able to screw it in further than if the engine were cold. Then, when that hot engine cools, it will really contract tightly around the threads of the plug and make it almost impossible to extract.

I suspect that the quoted advice comes from the fact that my explanation and advice are too complicated. So the advice is simplified to "don't change plugs on a hot engine that has an aluminum cylinder head" (or even an iron one for that matter, though the problem doing so will cause is much less severe). Whichis the advice that is normally given.

To me this analysis and advice means that if you have a problem plug that you are having a difficult time extracting from an aluminum head, get the motor up to operating temperature and try again. I think you will be surprised. But don't ever put a steel plug in a hot engine, but if you must, torque it very lightly!!!

On another note, I seem to recall from my Corvair days that the advice against the use of Never-Seeze or the like was due to the insulating properties of some formulas. You need to have a good ground from the plug to the head, and some compounds act as a barrier to the flow of the current. That said, I have never had a problem with an engine from using it, so the issue may be more theoretical than real. However, when I removed a plug in my '03, I reinstalled it "dry". It came out easy enough, so I wasn't afraid that it would seize in the hole. I have removed plugs in other motors at 100k and never had a problem so it seemed to me that the advice against use of anti-seizing compounds is legitimate.

Yes, I know:

1. There's always a first time
2. Better safe than sorry
3. Experience keeps a hard school, but a fool will learn in no other.
4. Etc.

But that's what I did. I weighed the advice against using it, considered the sources of that advice, and then considered that I haven't had any problems yet, and decided to stick with the factory and plug manufacturer recommendation.

Mark
 
#26 ·
:thumbsup:

Just replaced my plugs yesterday. Used AC Delco 41-103s. No anti-seize.
Took about 2 hours, only because I took my time and also cleaned the throttle body at the same time. I was a little worried about that #6 plug way in the back, but it was easy!! Also, had to fight to get that #1 coil pack out, but I eventually worked it out.

Thanks for the post. It was right on point and made the job alot easier.
 
#27 · (Edited)
#29 ·
I'm not for a second going to dispute your logic, because frankly I'm just not that smart and don't know enough about it.

But I'm curious - does anyone know what they usually do at the dealerships? I'm not saying that the dealerships are the know all/end all for this type of thing, just wondering what the common custom is!
 
#30 ·
Just did my plugs. Piece of cake. Don't let the back one scare you. With the right length socket extension, there is plenty of room. Pulled and cleaned my throttle body in the process. Again, piece of cake. I spent most of my time arguing with the little grey connector locks on all of the electrical connectors.

Great write-up on the throttle body:
http://forums.trailvoy.com/showthread.php?t=43912
 
#32 ·
Just did my plugs. Piece of cake. Don't let the back one scare you. With the right length socket extension, there is plenty of room. Pulled and cleaned my throttle body in the process. Again, piece of cake. I spent most of my time arguing with the little grey connector locks on all of the electrical connectors.

Great write-up on the throttle body:
http://forums.trailvoy.com/showthread.php?t=43912
IMO It is much easier to leave the wires attached. Just move the coil off to the side. DO NOT let the coil hang from the wire.:m2:
 
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