Guide to changing Trailblazer / Envoy 4.2L I6 Spark Plugs w/ Images & Google Doc URL - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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  #1  
Old 03-05-2011, 03:29 PM
Mageler Mageler is offline
Junior Member
 
2005 Chevy TrailBlazer LS
Silverstone Metallic 4.2L I6 AWD
Join Date: Mar 2011
Location: Cincinnati, Ohio
Posts: 1
Exclamation 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/lcsunshine...EzO WFh&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!

------------------------------------------
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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  #2  
Old 04-17-2011, 11:49 AM
bill_duval bill_duval is offline
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2004 GMC Envoy SLT XUV
Graphite Metallic 4.2L I6 4X4
Join Date: Nov 2009
Location: Durham, NC
Posts: 8
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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  #3  
Old 05-01-2011, 04:30 PM
AdamXL AdamXL is offline
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2004 GMC Envoy SLE XL
Summit White 4.2L I6 4X4
Join Date: Apr 2011
Location: South Bend, IN
Posts: 4
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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  #4  
Old 05-02-2011, 02:48 PM
es44ac es44ac is offline
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2002 Chevy TrailBlazer LS
Midnight Blue Metallic 4.2L I6 2WD
Join Date: May 2011
Location: houston, tx
Posts: 2
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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  #5  
Old 05-02-2011, 02:50 PM
es44ac es44ac is offline
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2002 Chevy TrailBlazer LS
Midnight Blue Metallic 4.2L I6 2WD
Join Date: May 2011
Location: houston, tx
Posts: 2
about step 3

in step 3, how can you tell if the coil packs are "properly seated?"
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  #6  
Old 05-04-2011, 12:03 AM
rzepplin rzepplin is offline
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2004 GMC Envoy SLE XL
Steel Gray Metallic 4.2L I6 2WD
Join Date: Mar 2010
Location: AZ
Posts: 2
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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  #7  
Old 05-04-2011, 07:36 AM
steevesj steevesj is offline
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2005 GMC Envoy SLE XL
Steel Gray Metallic 4.2L I6 4X4
Join Date: Aug 2009
Location: Willsboro, NY
Posts: 24
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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  #8  
Old 05-04-2011, 02:15 PM
rzepplin rzepplin is offline
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2004 GMC Envoy SLE XL
Steel Gray Metallic 4.2L I6 2WD
Join Date: Mar 2010
Location: AZ
Posts: 2
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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  #9  
Old 06-07-2011, 11:57 PM
chevy_kawi_guy chevy_kawi_guy is offline
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2006 Chevy TrailBlazer LS
Graystone Metallic 4.2L I6 4X4
Join Date: May 2011
Location: angier, nc
Posts: 28
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.
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  #10  
Old 07-01-2011, 09:07 AM
Djsthe1 Djsthe1 is offline
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2003 GMC Envoy SLT XL
Dark Gray Metallic 4.2L I6 4X4
Join Date: May 2010
Location: Waldorf Md
Posts: 5
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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