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2005 chevy trailblazer_ls
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Guide to changing Trailblazer / Envoy 4.2L I6 Spark Plugs w/ Images & Google Doc URL

Hey Every Body

I am new to the forum and wanted to share with everyone a guide w/ images I just got done putting together with step by step directions, tools needed, and typically over looked details that a first timer changing their plugs on there Trailblazer / Envoy should know.

I have it here as web based Google Doc Version.

https://docs.google.com/a/lcsunshin...TEtOWEyZi00NzNhLTg1ZDMtZTllMTgyODEzOWFh&hl=en

The text based version is below. Message me if you'd like the PDF version, you can also download the guide from the Google Docs Link above.

Enjoy!
Mageler

Be on the look out for my Step by Step guide to changing out the fuel sending unit in the next few weeks!

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How to change the spark plugs on a 2005 Chevy Trailblazer 4.2L I6
Step by Step Guide

Tools / Items Needed:
• Flat head Screw driver
• Socket wrench
• 10mm socket
• 5/8 Spark Plug socket
• 1 – 6” or 9” Socket Extension
• 1 – 3” Socket Extension
• 10mm open ended wrench
• Breaker bar or metal pipe (for leverage on the end of the socket wrench; used on the 6th spark plug just under the firewall, this one is a knuckle breaker, disregard if you have a long handled socket wrench)
• 6 pack of beer or fresh pack of cigarettes (Ether of these are an essential tools if you partake)
• 6 ACDelco 41-103 Iridium Spark plugs or preferred brand(ACDelco Spark plugs come pre-gapped from the factory at .043 but double check to make sure they are correct and did not change during shipping)
• Anti-seize compound (Not a requirement put good to apply to the threads of the spark plug for the next guy who may have to change out the plugs)

Step 1:
Remove the Air Resonator by undoing 2 - 10mm bolts on the left hand side, loosening the clamp around the air intake tube to the right of the mass air flow sensor, and the clamp where the air resonator joins the throttle body. Be sure to detach the mass air flow sensor wire from the resonator by undoing the plastic clip.

Step 2:
Now that you have removed the air resonators you have exposed the top of the coil packs of the 4.2L Inline 6 Engine. Each coil pack is held down by a 10mm bolt. I choose to start one spark plug at a time and work my way from plug 6 (under the firewall) and forward.

Step 3:
With the 10mm socket loosen the bolt which holds the coil pack in place. No need to disconnect the wire there is plenty of play to pull the coil pack up and set it to the side.
Plug 6 is the hardest one due to lack of maneuverability; this is where the breaker bar or pipe comes in handy to loosen the tightness of the plug. Once it is lose you can put the bar or pipe to the side it should not be needed for the rest of the rest of the plugs.
With the 5/8’s spark socket on the end of ether a 9” extension or a 6” & 3” Extension remove the plug. Make sure nothing falls into the hole. Now take your new spark plugs and insert it into the end of the 5/8 spark plug socket, should you choose; apply a thin bead of anti-seize to the spark plug threads. Insert the spark plug into the hole and start to tighten by hand to be sure you do not cross thread. Tighten the plug; be sure not to over tighten for fear of snapping the plug off, use your best judgment. Not reinsert the coil pack being sure the it is properly seated, and tighten the bolt back down.
Repeat above for plugs 6 through 2. Plug 1, closest to the front requires special attention see next step.

Step 4
Plug 1 is not too hard to remove but does require special directions because there is a plastic wire channel/guard which runs across it. Undo the bolt using the 10mm open ended wrench. Once the bolt is loosened slightly pull up on the coil pack, rotate about 90 degrees to the left while at the same time slightly tilting at a 45 degree angel towards the wind shield to remove the coil pack and clear the wire channel / guard. Now return to step 3 direction when it comes to changing out the spark plug.

Step 5
Now resemble. Be sure to tight the air intake tube clamp on the right, and left where the resonator connects to the throttle body. Tighten down the 2 bolts which hold down the air resonator; don’t forget to re-clip the mass airflow sensor wire just behind bolt 2 on the resonator.
Note: Be sure to check the tube which connects from the air resonator into the engine. This tube is located under the resonator on the left in line with plug 1.

That’s it! You are all done! Now drink a beer, smoke a cigarette, or take your girl out for a ride. Enjoy the regained power you’ll get in your Trailblazer or Envoy.

My last note here: GM/Chevy say the stock plugs are good for up to 100k miles; however I have found in my truck and my friends that they tend to show sign it is time for a change between 75k -90k on average. When I removed my plugs at 88k they were way gone(I do a lot of long distance travel for work and drive hard), hell the average gap on the plugs was between.051-.054 ; the plugs showed signs of bridging and were blackened. My fuel economy sucked 12-14 mpg and the truck ran like crap. Now I got the mpg back up to between 18-20 mpg, I changed my oil, new tires, and truck runs great again!
 

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2004 gmc envoy_slt_xuv
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Plug #1

Thanks for this post - was very helpful. Had a challenge with #1 and wanted to share that I was able to get some additional clearance by removing the top cover of the wire channel. Takes a bit of prying with a small screwdriver and there are quite a few tabs to undo, but it does come off. I then had enough clearance to get a 10mm socket on to remove the coil pack.
 

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2004 gmc envoy_sle_xl
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This really helped me figure out my misfiring issues. But to take out coil 1 I didn't have to take the channel off I just kinda lifted up on it enough to pull the coil up and out. Great post thought!!
 

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2002 chevy trailblazer_ls
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Easiest spark plug change i've ever done. But, my engine was idling rough, changed the plugs, gapped them right etc.... But now after changing them out, the engine runs more rough than it did before. I called the chevy dealership, they told me drive it around a while and see if it smoothes out. i disconnected the battery cable and let everything reset and it ran smooth for less than a minute. Do the coil packs go bad? its acting like its missing...something aint quite right.
 

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2004 gmc envoy_sle_xl
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I just finished replacing the spark plugs and now my GMC runs rough and has no power, so can anyone answer why?
 

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2005 gmc envoy_sle_xl
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For those thinking about waiting till 100,000 to change plugs I would not wait. I just did mine at 60,000 and most were very worn (there wasn't must left of the center electrode). The old plugs were the AC Delco 41-981 platinum. I replaced them with the 41-103 iridium.
 

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For anyone still having problems, on step 3 the coil pack will seat all the way to the gasket. If the coil pack seats with resistance then just pull back out and tip it at a forward angle and it will seat properly. After that I cleaned the throttle body and now my Envoy runs smooth. Thanks for the tip RayVoy.
 

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2006 chevy trailblazer_ls
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ok guys, not doubting anyone here but why is it that my manual calls for ac delco 41-965 plugs with a gap of .050" ?

the plugs that came out were the 41-103 and the gap was .040"

the gap on the new 41-103 were also at .040" do i leave them at .040" or do i open them up to .043" ?

i know i'm prolly splitting hairs on the gap but i tend to be a little anal about specifications and try to get them as close as possible to what they're supposed to be.

i've been slacking with my maintenance but i'm pretty amazed at how well the plugs look at 100k and first time being changed.

also cleaned the throttle body for the first time and it wasn't very dirty either. a LOT cleaner than some of the pics of others i've seen on here with less mileage.

one thing i'd like to add to this procedure. i didn't see it in the step by step instructions here but it's a good idea to blow out the plug wells with some compressed air BEFORE you pull the plugs, just in case some dirt made it past the seal on the coil packs. it'll keep anything from falling down into the cylinder when you pull the plug. :thumbsup:
 

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2003 gmc envoy_slt_xl
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Just to add to the tool list, a pair of needle nose pliers. My 5/8 plug socket kept sticking to my plugs so I had to keep fishing it out. Good write up and helpful tips!
 

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I replaced my plugs a couple months ago. Didn't see this write up before hand, but I basically did exactly what you have written.

My additions though:
I did remove the wire channel to get at plug 1, just makes it easier.

If you do put on anti-seize, make sure it's the kinds meant for spark plugs. Something like the Permatex Copper anti-seize. You want to make sure it is conductive to electricity so you get a good spark I didn't use anything on my plugs. You may also want to add a shot of di-electric grease to the connection between the plugs and the coil packs. There's some in there already, but you loose some with the old plugs.

The reason I replaced them was because of a misfire on cylinder 1. After replacing them, still had the misfire. I didn't want to buy a new coil pack if I didn't need it, so I swapped the coil packs between 1 and 2, and the misfire showed up on cylinder 2. So, went and picked up a new coil pack and put it in plug 1, moved the original #2 pack back to the #2 plug, and everything is good. :thumbsup:
 

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ok guys, not doubting anyone here but why is it that my manual calls for ac delco 41-965 plugs with a gap of .050" ?

the plugs that came out were the 41-103 and the gap was .040"

the gap on the new 41-103 were also at .040" do i leave them at .040" or do i open them up to .043" ?
A little dated on the reply here, but noticed that no-one had actually addressed it...

The 41-103's are the currently recommended plugs for the 4.2 I6.

The 41-985's are for the V8 engines.

That's stuff out of the later owner's manuals.

I'd leave the plugs at .040". That gap will work, and there's less chance of
breaking the electrodes. The newer alloys tend to be rather hard and
brittle. If they're already knocked off of .040", you can try adjusting them,
but some of the more generic gapping tools aren't up to the task.

Good Luck!

Chris
 

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Plug 6

I just finished replacing the plugs on my '07 TB LT. Plug 6 took and hour and the rest took 30 minutes. I didn't pay attention when I was ratcheting the 6 plug out and the plug socket went all the way down on the plug while the ratchet jammed under the firewall. I had to pry the ratchet out enough to change it to the on position and put the plug back down to where it was loose enough to turn by hand but I could get the ratchet out.I tried several methods to remove the plug before taking a 13/16 socket and putting duct tape inside it. I jammed it down on the other socket and was able to unscrew the plug. After finishing the job, I took my TB for a ride and immediately saw at least a 3mpg improvement. My mileage was 67000.
 

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Just put in the AC Delco Iridiums (41-103), they came pre-gapped at .038". The manual shows .042" and the old plugs were gapped to .038". I decided to keep them .038", everything runs smooth.

We also put the same plugs in another vehicle but the gap was larger. Be careful if you need to gap with one of those cheap coin style gap tool, the tips break very easily!
 

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Just put in the AC Delco Iridiums (41-103), they came pre-gapped at .038". The manual shows .042" and the old plugs were gapped to .038". I decided to keep them .038", everything runs smooth.

We also put the same plugs in another vehicle but the gap was larger. Be careful if you need to gap with one of those cheap coin style gap tool, the tips break very easily!
I took my 41-103s and didn't even check gap. They were protected by the sleeve and I wasn't about to mess with them. I just drove from Jacksonville to Atlanta today, 365 miles, and got 20.6 mpg driving 72 to 75 mph. I topped off just before I left and topped off when I got here. My econ showed 21.2 so that's not far off. After reading all the posts about towing, I'm really looking forward to pulling my travel trailer to the Florida Panhandle to go scalloping next week, it should do a lot better than my Toyota Tacoma. BTW, can my P245 tires actually cause my mileage to look less than it really is since the standard tires are P235?
 

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Hey,

I folllowed these directions and it took about three hours to change the plugs and clean the throttle body. Although it took longer than expected I had never attempted anything like this so I was happy that it turned out well and I saved a little money by doing it myself. The number six cylinder was a terrible pain and I believe I spent as much time on that one than all the others combined. Thanks for this guide though, I feel like my TB has a little bit of new life now!

~~Rich
 

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2006 gmc envoy_sle
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Thanks Mageler for outstanding instructions. Fo me #6 was quite easy. I left out the #5 coil pack until I was done with #6. Used a 1/4" socket wrench with short extension for the coil packs. Worked great on #1. My spark plug socket didn't have the insert so I had to stick my big fingers in the head to get the plugs out. Hardest part! Also for putting the new plugs in I used the old trick of using a piece of tubing on the top of the plug to start it in. In my case it was tubing for my fish tank. Hey, it worked! Truck runs 10 time better! Total time spent? Get this! 45 minutes! I bought the Champion Iridiums from Rock Auto with a $2.50 rebate per plug. Sweet deal! Thanks again for the very simple instructions! I love this place! :grouphug:
 

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Wow! MPG increased from 15.6 to 19.2 in the city just by changing plugs! That was on the first tank. Let's see what happens on the next tank.

:tiphat
 

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great

thanks for taking the time to put those instructions together. just a quick note of my experiance incase anyone else sees the same thing. My truck starting missing and was running terribly. I stopped and hooked up the ODB and it said a miss on 4. Then I turned the engine off to unhook the ODB and the truck would not start again. Completely dead - even the display was saying "unknown driver". After some swearing and calling the boss to say I wouldnt be in, it started right back up again - I was 10 miles from home and nursed it back slowly on back streets. After about 5 miles the gauges went crazy and all the lights came on - 4WD, Check Engine, Air Bag - all of them. I stopped and turned the engine off thinking I had really killed it this time - I connected the ODB and it restarted with just the Check Engine light lit but I got an P0300 random misfire code. I stopped at the store leaving it running and bought 6 Iridium plugs and a coil pack ($105 locally here in PA for all). Followed ur instructions and its as good as new... No idea why the computer wigged out like that... :undecided
 

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2002 chevy trailblazer_ls
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Easiest spark plug change i've ever done. But, my engine was idling rough, changed the plugs, gapped them right etc.... But now after changing them out, the engine runs more rough than it did before. I called the chevy dealership, they told me drive it around a while and see if it smoothes out. i disconnected the battery cable and let everything reset and it ran smooth for less than a minute. Do the coil packs go bad? its acting like its missing...something aint quite right.
This is the exact issue I'm having. I did notice the old plugs had a different number on them than the new ones that went in. The new ones are ac delco iridium 41-103. I need help figuring this out.
 
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