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2006 gmc envoy_sle
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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.

A previous poster identified a coil pack as the problem. Swap a known good cylinder pack with the missing one and see if the problem changes cylinders. If it does you have your solution. If not, it could be as simple as a bad plug. In which case I would do the same with the plugs swap them and see if the issue moves with it. Process of elimination. The simplest solution is usually the right one. Good luck.
 

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2004 gmc envoy_slt_xuv
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2 Posts
change the coil pack

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.
I would say almost without a doubt it is the coil pack - do you know which cylinder? if not you will have to start switching out one at a time until you find it. Try #4 first (4th from the front) as that one seems to fail most often due to moisture getting into it from the hood seal directly above.

Good luck and let us know if it worked. :)
 

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2004 isuzu ascender
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2 Posts
Good write-up! I wanted to add that for the #6 cylinder, take the #5 coil pack out and use a ratchet wrench. It worked wonders and the whole project took less than 30 minutes! Here's hoping I see some better mileage. :thumbsup:
 

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gmc envoy_sle
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30 Posts
Splendid writeup on plug change. 2002 Envoy, 98k miles,Had a bad skip, changed plugs, still had skip, did the old shadetree method...unplug each coil till you track it down. Swapped with a known good one, skip moved with coil. Then inserted old plug into suspect coilpack,grounded plug, started engine...no spark, did same with known good coilpack, good spark, replaced bad coilpack....everything running fine.
http://forums.trailvoy.com/images/s...rums.trailvoy.com/images/smilies/thumbsup.gif
Thanks for a great,and informative forum......This is my first post..Bill
 

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gmc envoy_sle
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30 Posts
Splendid writeup on plug change. 2002 Envoy, 98k miles,Had a bad skip, changed plugs, still had skip, did the old shadetree method...unplug each coil till you track it down. Swapped with a known good one, skip moved with coil. Then inserted old plug into suspect coilpack,grounded plug, started engine...no spark, did same with known good coilpack, good spark, replaced bad coilpack....everything running fine.
http://forums.trailvoy.com/images/s...rums.trailvoy.com/images/smilies/thumbsup.gif
Thanks for a great,and informative forum......This is my first post..Bill:thumbsup::thumbsup:
 

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2005 chevy trailblazer_ls
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6 Posts
Thanks for the guide! I successfully changed out the plugs in my 2005 Trailblazer for the first time today. However, like some others here, my vehicle now idles rough and has a tremendous loss of power especially while accelerating. I'm quite frustrated :mad: I know the plugs are in right and the coils are seated properly. I put in the AC Delco 41-103 iridiums and I double checked the gap at .043 before I installed them. I'm at 120K (I know, slacked on my 100K plug change) but haven't had any issues with performance until I changed the plugs today. At this point I wish I would have just left it be! Any ideas as to why this is happening now with brand new plugs?? I also got a code now, pretty sure it's a mis-fire on one of the cylinders since the problem didn't start until I changed the plugs...but something definitely is not right. I'm considering just taking it to the shop to see what they say. I hate to do it, but I gotta have my TB up and running right! I disconnected the battery for the night just to see if that has anything to do with the situation. Any advice before I cave and just take it to a shop would be greatly appreciated. Thanks!!
 

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2004 gmc envoy_sle
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18 Posts
I would check to make sure I didn't crack one of the plugs while putting them in first before taking it to a shop.
 

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2004 chevy trailblazer_lt
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Thanks for the guide! I successfully changed out the plugs in my 2005 Trailblazer for the first time today. However, like some others here, my vehicle now idles rough and has a tremendous loss of power especially while accelerating. I'm quite frustrated :mad: I know the plugs are in right and the coils are seated properly. I put in the AC Delco 41-103 iridiums and I double checked the gap at .043 before I installed them. I'm at 120K (I know, slacked on my 100K plug change) but haven't had any issues with performance until I changed the plugs today. At this point I wish I would have just left it be! Any ideas as to why this is happening now with brand new plugs?? I also got a code now, pretty sure it's a mis-fire on one of the cylinders since the problem didn't start until I changed the plugs...but something definitely is not right. I'm considering just taking it to the shop to see what they say. I hate to do it, but I gotta have my TB up and running right! I disconnected the battery for the night just to see if that has anything to do with the situation. Any advice before I cave and just take it to a shop would be greatly appreciated. Thanks!!
It's always a good idea to at least get the code, but two things to look at:
-As mentioned by garold99, a possibly cracked plug
-throttle body.

You didn't mention if the throttle body had ever been cleaned, and if you
disconnect the battery for 15-30 minutes, it resets the PCM operating
parameters for the throttle body. If the throttle body is dirty and the PCM
is trying to run with the baseline "clean" parameters, it tends to make the truck run like cr*p.

Worth a look, at least.

If the code points to a specific problem, like a particular plug, you can play
coil swap and see if the problem travels. If it does, there's a coil pack problem.
If it doesn't, either the plug is bad (and yes, they can actually be bad out of the
box) or there's a wiring problem to the coil.

Something else that just occurred to me is that you may have a vacuum line
that has been knocked loose. It's not hard to knock one loose while working in
the engine compartment.

Good Luck!

Chris
 

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2003 chevy trailblazer_lt_ext
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98 Posts
Excellent write up with great pics and step by step instructions.

I replaced my plugs a few years back when I was at 100K, but it is time for me to do it again, as I now have 190K on my TB.

On my way to 200K miles and all smiles! :D
 

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2003 chevy trailblazer_lt_ext
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98 Posts
Ok, I swapped all my plugs yesterday, along with cleaning the throttle body, and my K&N air filter. I have not driven it yet to see any change in gas mileage, but check out my #6 plug. UGLY! I know people say moisture can get in there and cause rust, but THIS MUCH??
 

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2005 chevy trailblazer_ls
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Thanks for all the advice guys. So the final outcome of my situation: Plugs were installed correctly and are working properly. All coils were properly seated...except for the #1 coil. I sputtered down to Autozone (which luckily is right down the street) and found the code to be just what I'd figured. Cylinder 1 misfire. So I sputtered back to my garage and let it sit overnight.
Got up the next morning and removed the #1 coil pack...of course the one that gave me the most problem the first time because of the wire channel that runs along the top of the 10mm bolt. This time I used pliers and pulled slightly up on the wire channel to get a better bite on the bolt. After I removed the coil pack...I noticed the bolt was broken off inside the head!! Lesson learned for the do-it-yourself-er...don't get too excited when re-tightening bolts! With that being said, I extracted the broken bolt from the head, which for this I just took the wire channel completely off. Those two plastic tabs require some special attention, but do spin out to remove the wire channel completely. With that out of the way, I went back to Autozone in my other car to get a new coil pack. Like I mentioned...lesson learned! Got it installed...correctly, without over-tightening, and was able to use a 10mm socket since the wire channel was removed. Put everything back together, and now my TB runs great! I would recommend removing the wire channel for better access to the bolt on coil #1. It takes more time, but is quite worth it.
 

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2005 gmc envoy_slt_xl
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8 Posts
Just changed my plugs as well. Thanks for the detailed info. Plugs #2 and #5 were soaked in oil around the threads. Is this normal?
 

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2005 chevy trailblazer_ls
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6 Posts
Thank you so much for this post, you just saved us about a grand because we have about 6 codes that are getting thrown and they all start with this one so hopefully this will correct all of them.:tiphat
 

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2005 chevy trailblazer_ls_ext
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112 Posts
Recommended spark plugs?

Bosch platinum 4 okay? if not what is a good plug
 

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2005 chevy trailblazer_ls_ext
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VIDEO of same procedue (for those who dont like to read)

http://www.youtube.com/watch?v=IhBebL0JeAs

A quick simple explanation of how to change spark plugs in a 2005 or later Chevrolet Trailblazer.

You don't need to be super handy to do this, and it will save you money!

* The only slightly difficult part is the removing the wire harness to get at the forward most spark plug. You just have to twist the white plastic piece so it slides into the black square hole and it will twist itself out. Then, you can remove the entire white piece by unscrewing it after the harness has been removed.
 

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2002 gmc envoy_sle
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3 Posts
Step three

The number 6 plug cracked while removing and I believe some material got in the whole. What do I do?

My engine now idles hard with a misfire and putters down the road.

Please someone help!
 

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2002 gmc envoy_sle
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Step three

What happens if you crack #6 while removing and some of the material gets into the hole?



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.
What happens if you crack a plug while removing and some of the material gets 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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2002 gmc envoy_sle
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152 Posts
Just finished changing the spark plugs at 96,000 miles. Won't say how long it took. Suffice to say that when I started the sun was shining. When I finished it was still shining (same day).

I had no problems with the old plugs. The Envoy was running great. When I finished, it ran like crap and threw code PO300 "multiple misfires". I tried everything. Even took out all plugs to check for cracks. Reinstalled coil packs. Pulled the battery cable to reset stuff. No good.

Then I cleaned the throttle body. All good after that. I suggest cleaning the Throttle body be part of any plug change.:m2:

Thanks for the the write ups. I must have read them all.:crazy:
 
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