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2002 gmc envoy_sle
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Throttle body

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:
I did all that too, but my voy still runs like crap. It feels like its misfireing but doesn't thow codes. Feels bogged down.
 

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2002 gmc envoy_sle
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152 Posts
I did all that too, but my voy still runs like crap. It feels like its misfireing but doesn't thow codes. Feels bogged down.
Did you remove the throttle body for cleaning or just spray the intake? If you're not throwing codes I'd guess the plugs and packs are okay. Air box put back right? I'd try the old battery cable disconnect and reset routine again after rechecking your work.
 

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2006 chevy trailblazer_ss_lt
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9 Posts
SS Trialblaer 06: Just did my Plugs yesterday and replaced them with NGK TR7 gap'd to 35 and PCM for Less Plug Wires. Cleaned the throttle body as well. Started up the car and it sounded like it was running a bit rough, but when I did a test drive it felt like it would hesitate and then bog down a bit. It also felt like it was sputtering. Not sure what this was. Checked the wires. Haven't checked the plugs yet though. Outside of a cracked plug what would should I look at? I dont think one of my coil packs would have gone bad from this and it would seem odd to think so. Thoughts?
 

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2006 chevy trailblazer_ss_lt
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FIXED: Went through the recommendations of the board and pulled all the plugs again. What I found was that cylinder #1 plug was cracked at the Ceramic. Put the old plug in temporarily and it ran like a dream. Oh well, first rule of thumb. Don't go by the torque specs too closely. Go a bit tighter than grip tight with the socket. Anything more than that will shred the plug. Also, careful on these heads since they are aluminum, I could see someone stripping it pretty easily.
 

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2002 gmc envoy_sle
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6 Posts
Replacing Plugs

Thanks, very much, Mageler for taking time to provide such a detailed procedure for replacing the plugs – it made it much easier for a 1st timer.
I can add that removal of the coil pack on my Envoy was very difficult until as suggested in a later post: 1) I removed the ‘snap on’ cover for the wiring channel 2) Lifted the two nylon pins securing the channel to the top of the motor. That provided enough play in the wiring harness to easily remove the coil pack.

I was amazed to find that the old plugs, with 106K miles, were still in good shape.

Ordinarily I would not have celebrated with a beer but since you included it as Step 6 I felt obligated to ‘follow instructions’!
 

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2002 gmc envoy_sle
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Spark Plugs

The original plugs were AC Iridium and I elected to not experiment. I installed: ACDelco 41-103 Iridium
 

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2002 chevy trailblazer_ltz
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3,250 Posts
41-103 is the only replacement. You risk misfires if you install anything else.
Not exactly true.

While I would always try to get the AC Delco's, NGK is the manufacturer of AC Delco plugs now. I ran a set of their Iridiums in my engine for 93K, and they were flawless.
 

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2002 chevy trailblazer_ltz
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....I was amazed to find that the old plugs, with 106K miles, were still in good shape......
I had the same thought both times I replaced the plugs......could have put many more miles on them, no problem.
 

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2003 gmc envoy_slt
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Thanks for the write up, this will be the first thing done in our "new" 03 Envoy with 126k. Seems like the previous owner wasn't as meticulous about some of these things as we are. :worried: lol
 

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chevy trailblazer_ls_ext
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i work on 2 different trailblazers my own and a friend of mine.
i found that that the spark plugs on these are very easy to change. the 2 "hurdles to this job is the wiring loom across the front for cylander #1.
i pried up the gromet that holds it down and pulled it (plastic loom) up and towards the radiator.
2nd hurdle is the last plug under the firewall. trick there is when doing the 5th plug in line is to leave that coil/boot out and it gives you much more room with a short extension and long handle ratchet it is not bad at all.
does everyone follow the torque specs on the plugs? 13 ft lbs? i did on both trailblazers with no problems.
it took me 45 minutes on the first one (plus a couple beers)
and only 30 minutes on the second TB.
both were in 120,000 mile radius and plugs looked decent.
 

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2002 chevy trailblazer_ls
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Good write up, I will be doing this later today if the weather cooperates.
I'm not a professional mechanic but have been working on cars most of my forty-mmmmm years and was a machine shop/parts counterman 10+ years and here are some pearls of wisdom on spark plug changes:

1. Torque spec IS very important, the #1 reason for a plug cracking is the socket coming into contact (tightening with ratchet at an angle) with the top of the plug, it doesn't take much to crack a plug, this is why new plug sockets have a rubber/foam insert to help prevent plug cracking.
2. Use anti-seize always
3. Use dielectric grease always
4. Take care gaping plugs, easy steady pressure on the electrode is best, I always check gap even with cardboard sleeves protecting them during shipment.
5. Generally speaking, the stock replacement is best (having said that, in my years of GM V-8 wrenching I found that the basic Bosch platinum plug was best, also as mentioned by another poster unless you can determine who the actual manufacturer is however the item may be made to different spec for the end vendor)

HTH, Bill.
 

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2002 chevy trailblazer_ls
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I just did this over the weekend. Thanks for the write-up! The #1 pack was way more difficult at first than #6.

I had the battery disconnected they whole time and when I started the truck afterwards I had really rough idle. I re-seated the first couple coil packs then while standing in front of the truck I made sure that all of the heat sinks on top of them were in a straight line. A couple had twisted a little, most likely causing my problems. I also disconnected the battery again for at least 30mins. After that, the rough idle was gone.

It's an '02 with just over 130k. I'm pretty sure this is the first plug change on the truck as I've had it since it had 35k miles or so.

Here's one of the old ones and a new one. I can't wait to top off and run a full tank to see what the difference is. I was getting just under 15mpg.

 

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2002 chevy trailblazer_ltz
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This forum is great it helped me alot i just changed my plugs yesterday but i could only change the 4 in the front and i couldn't reach the 2 at the end But i will try to get the right tool next time and i will change them for sure thanks a million for that awesome thread.:)
 

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2006 gmc envoy_slt
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With respect to the #6 plug, I used two 3" extensions.

Once I'd changed #5 I left the coil pack off.

A single 3" extension with a 10mm socket got the coil pack off easily enough, then I removed the 10mm socket, and fitted my plug socke to another 3" extension.

With just the socket and short extension, there's pleanty of room to get in on the old plug, then fitteng the second extension plus ratchet, puts the handle in a good position.

Once loose, remove the ratchet and first extension, and there's no problem getting the plug out.

Then do it in reverse to fit the new one, and but the two coil packs back on.

For #1 access to the 10mm on the coil pack, I have a flex drive that worked great, but a short UJ would work too.
 

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2005 chevy trailblazer_ls
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Plug #1 Sucks

So...I just changed out the plugs, the back plug,:undecided heh...you would think would be the hardest, NOPE!!, cake...the front one, just kick me in the jhar sack:eek:, that one sucks... why they put that wire tray on top of the nut is beyond me:confused:. I spent more time trying to pry off those little white plastic holders than the whole job itself. But I must say, after that, started up, smooth running and saved me well over $150 for some mechanic to do it. Happy plug changing!!:D
 

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2002 chevy trailblazer_ltz
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25 Posts
Great thread!

I just changed my plugs as past of a "tune up". I started with the fuel filter, which turned out to be a nightmare due to rust and it probably never being changed. After the filter change, it developed a misfire. I diagnosed it as a bad coil, which is ironic, as it happened immediately after starting it up after the filter change. I replaced the bad coil, then removed the throttle body. I cleaned the throttle body since it was there already. I highly recommend cleaning the throttle body when changing plugs. It takes an extra 20-30 minutes but it's very well worth it. After all this, I finally changed the plugs which had about 125k miles on them and noticed a HUGE difference after starting it up.
 

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2005 chevy trailblazer_lt
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3 Posts
oil?

When I removed the coil packs there was a bunch of oil sitting down in with the spark plug. What causes this and should I be worried?
 
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