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2003 gmc envoy_slt_xl
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Discussion Starter #1
As this forum gave me so much in learning about my vehicle, I thought I'd go ahead and give something back, and document my new found knowledge and show you the steps on how to change your 4.2L I-6 Spark Plugs.

Note: Common sense would dictate that you go ahead and do a throttle body cleaning in conjunction with the spark plug replacement; only 4 bolts and 2 connectors remain to remove the throttle body from the manifold, and the effort is well worth the time.

Tools Needed:
8 mm Socket
10 mm Socket
Regular Flat Blade Screwdriver (Optional)
3/8" Spark Plug Wrench
Socket Extensions

Supplies Needed:
Throttle Body and Carb Cleaner (CRC or Equivalent)
Shop Rags
Anti-Sieze Compound (Loctite or Equivalent)

Parts Needed:
6 AC-Delco Iridium (PN 41-103) Spark Plugs (As per AC Delco Service Bulletin, 103's are pregapped at manufacturer, and do not require gapping)

Instructions

Spark Plugs are accessed by removing the Resonator / Pre-Plenum (Marked Vortec 4200), located at the top of your engine.



Begin by removing the Fuel Pressure Regulator Vacuum Line; slight twisting pressure will suffice.



Then, remove the Air Box Hose Clamp, using an 8 mm socket, or optionally, a regular flat blade screwdriver.



Next, remove the throttle body hose clamp, using the same socket or screwdriver.



Remove the forward Resonator attach bolt, using a 10 mm socket.



Followed by the aft Resonator attach bolt, with same 10 mm socket.



After removing the wire loom clamp located just aft of the rear Resonator Attach bolt, you can now lift and remove the resonator; please notice the Crankcase vent hose under the Resonator attached to the valve cover; this just slides off.

You will now see the 6 coil packs exposed; Cylinders are numbered 1 through 6, with Cylinder 1 located at the radiator side, Cylinder 6 at the firewall side.



Using a 10 mm socket, remove the single bolt attaching the coil pack.



Using slight upward pressure while rocking side to side, pull the coil pack up and out of the spark plug well, and lay it to the side.



You can now see the spark plug at the bottom of the well; using a 3/8 spark plug socket, remove and replace each of the 6 spark plugs. Before inserting the new spark plugs, apply anti-seize compound to the threads of the new plug; this will aid in removal during your next plug change.

[Note: you will need to move the wire loom that runs left to right over Cylinder 1 coil pack to access the bolt and remove the coil pack. I found the easiest way to do this is to remove the loom conduit cover, and pop / break the 3 plastic retaining clips that secure the conduit to the engine; clips are not needed, as the Resonator / Plenum when reattached holds the conduit securely]

Here’s a picture of the old spark plug (not to bad, considering they have about 180K Miles on them)



In comparison, here’s what a new spark plug should look like:



As noted; given you have the Resonator / Plenum already removed, you really should go ahead and clean your Throttle Body.

Instructions on cleaning our throttle body can be found here: http://forums.trailvoy.com/showthread.php?t=51619

Please note: it is easiest to do this with Cylinders 3 and 4 coil packs removed; it makes accessing the bottom throttle body bolts much easier.

Here is a picture of the manifold side of the throttle body pre-cleaning.



Here’s a shot of the intake side of the TB pre-cleaning.



Here’s the intake side of the TB after being cleaned.



Just retrace your steps to reassemble; details to remember are to remember to reattach the Crankcase Vent hose under the Resonator, and don't forget your two connectors on your throttle body.

Hope this helps any of you contemplating doing the job yourself; with a quote of $130 to $180 from my local dealer to change plugs, I save myself close to $100 by doing it myself.
 

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2003 gmc envoy_sle_xl
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145 Posts
dont you like doing things yourself and saving money. well, on neeeds not necessarily wants.
 

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2004 chevy trailblazer_lt
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1 Posts
:thx the walkthrough is great! my only question is about the reseating of the boots on the plugs once installed. i'm accustomed to the "click" when a normal plug wire is reattached, but since these have the coil on top, i'm unable to tell if the boot made a good connection to the plug.

i can feel a bit of "vacuum" pressure (from boot to plug) when i pull up on it, so the boot is on, but i'm concerned about a good connection.

i sent in my pcm to pcmforless, so i can't start it up to be sure it's ok, at least for a couple days.

reassurance anyone?

Thanks again!
 

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2002 chevy trailblazer_ltz
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3,250 Posts
:thx the walkthrough is great! my only question is about the reseating of the boots on the plugs once installed. i'm accustomed to the "click" when a normal plug wire is reattached, but since these have the coil on top, i'm unable to tell if the boot made a good connection to the plug.

i can feel a bit of "vacuum" pressure (from boot to plug) when i pull up on it, so the boot is on, but i'm concerned about a good connection.

i sent in my pcm to pcmforless, so i can't start it up to be sure it's ok, at least for a couple days.

reassurance anyone?

Thanks again!
Just make sure that you lower the coil pack straight down into the plug well. It has a spring coil at the end that contacts the pug tip, and will sit slightly above the valve cover until you tighten the bolt down.

Word of Caution!!! Do NOT tighten the coil bolt too tight....if you snap it off, you will be in a world of hurt if the threaded part stays in the bolt hole. Just snug the bolt down and that's it.

If the engine idles nice & smooth after re-assembly, then you got all the packs back on correctly.

Oh, and if you have access to an air compressor, put a clean rag into the throttle body opening, and blow any dirt out of the spark plug well BEFORE you remove the spark plug. Or a portable air tank w/ air nozzle will work too.

And I agree with the above OP about using a THIN film of never-seize on the plug (and also the coil pack threads).
 

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2004 gmc envoy_slt_xuv
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That was EASY!!

Thanks for the fantastic walkthrough! I've never done anything like this before (changed regular plugs w/ wires, but that's it), and your step-by-step made it very easy to follow. I also removed and cleaned the throttle body assembly, and my '04 Envoy XUV runs as smooth now at 111K as when I first bought it with 32K. Plugs were in pretty bad shape, and the TB was totally black on the manifold side. Looks and rus like new now!
 

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2004 gmc envoy_slt_xuv
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Addendum to "That was Easy!!!"

Almost forgot to mention that I did the whole thing in only 2-1/2 hours, and that included a 25-minute round trip run to the parts strore in the middle to buy a new air filter and a 5" ratchet extension. Those plugs are in there deep!
 

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2003 chevy trailblazer_lt
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4 Posts
Let's try it.

In addition to some people's replies I also have never changed anything but conventional plugs. I was in the middle of trying to figure it out on my own and wanted to make sure I wouldn't make a mistake and stumbled on this perfect tutorial. I'll post a reply when I'm done, which should be in a couple hours according to the previous post...
 

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2003 chevy trailblazer_lt_ext
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268 Posts
Hope this helps any of you contemplating doing the job yourself; with a quote of $130 to $180 from my local dealer to change plugs, I save myself close to $100 by doing it myself.

Not to mention what the dealer would have tacked on your bill to clean the throttle body:tiphat
 

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2003 chevy trailblazer_lt
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Finished

I was done about an hour ago and I really took my time making sure I didn't ruin any parts or break any clips. I followed all the steps and applied anti seize to all the bolts i took out and replaced. My throttle body was as dirty as the picture and I cleaned it up nicely. It seems to run ok but its tough to tell if its any better. It had stalled on me in the past and the plugs have been in there for what I think was 170000 km.

Thanks for the tutorial!
 

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2006 chevy trailblazer_ls_ext
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85 Posts
Hey thanks for the post emtwo, was a great help!

The only thing I might add is that when it comes time to remove the old spark plugs, and this goes for anytime you are removing a bolt etc that comes out tough and you are afraid of snapping something,:mad: is to alternate loosening and tightening in small increments until you think the bolt will come out easier. Loosen a little, tighten slightly and repeat. Sometimes it even helps on the initial loosen, if it feels like the plug isn't budging, just tighten a very slight amount.

Also make sure you have an assortment of extensions. For the plugs close to the front of the engine I think I used a 6 inch extension. For the rear plugs I had to use a couple of smaller extensions because of space restrictions.

I put silicone dielectric grease on my spark plug ends where the coil pack plugs into. From the looks of things I probably didn't need to, but old habits are hard to break! And yes anti-seize on spark plug threads...

Lastly I unplugged my battery for 1/2 hour to let the computer relearn the new spark plugs and cleaned throttle body.

Thanks again!:)

-Jerry
 

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2003 gmc envoy_sle_xl
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Nice tutorial

Hey thanks for the great tutorial!

I used this as suddenly this morning the wife calls in a panic saying the car is dying! when I finally got to it and watched listened to it, and learned from trailvoy that it was the coilpack going bad, this was a HUGH help. But i'm having a small problem. I decided to replace the plugs since i've had it since 115,000 and put delco plugs in. (unplugged the battery while doing this). Now that I have replaced everything and the truck is running much better, I decided to take for a test drive. It seems to have a lack of power then from before the problem/parts swap. I replaced one coil pack and all the plugs (from bosch platinum two) ( to delco xx-xxxx). Is it still learning the system or do i still have a problem. (i also cleaned the throttle body). Any suggestions?
 

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2004 chevy trailblazer_lt
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I gave replacing my plugs today a go, I put the 41-103 Iridium plugs in and it ran like dog crap. I called autozone and they said that the plugs won't work with the truck, I wish he could have told the lady the day before she sold me them. I need platinum plugs, they didn't have any anywhere so I had to order them online and had to put old plugs back in.:hissy::hissy::hissy::hissy::hissy::crazy:
 

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Premium Member
2003 chevy trailblazer_lt_ext
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268 Posts
maybe it wasnt the plugs, did you disconnect the battery?, which would erase any learned compensation for a dirty throttle body and run like crap, or maybe one of the coil packs wasnt seated properly which would cause a miss, those are the correct plugs for this truck, whoever told you otherwise is not giving you good information, check all the 41-103s to see if they are correctly gapped as well
 

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2004 chevy trailblazer_lt
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I did try and gap them but I don't think I was suppose to though and it ran even worse and would die. I'm going to give the Platinum plugs a try, I think the 41-103 are for iridium and platinum?. I only have the ramp style gap and that I think would break the tip off the plug? When I first tried to check the gap 1 plug was only at .35 I believe. I can give the throttle body a cleaning, it doesn't look too bad now. With the old plugs back in though it ran better than when I first put the irdium plugs in.
 

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2006 chevy trailblazer_ls_ext
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You have to understand that a lot of people who work at the chain auto part shops really do not know a whole lot - if they did, they would be working as a mechanic somewhere else making better money. (unless bad back, etc) So do not get your hopes up when dealing with them, I just assume they really don't know anything and am pleasantly surprised when they do.

The AC-Delco 41-103 are the correct plug. There were older plugs that your vehicle came with, but have since been DC'd by GM and now the 41-103 is the correct plug.

They are supposed to come pre-gapped from GM at .043 inches, which is what my 06 service manual calls for. When I installed my plug I used my gapper very very gently just to make sure that the .044 would not go into my plug, and then checked that .040 would fit into the plug. (I have several gappers but couldn't find any of them :no: so was stuck with the one I could find) You can damage those tips by gapping the plug so be careful. These aren't the old champion plugs you threw in your lawnmower after gapping and bending back and forth until the size is right...

So did you try unplugging the battery for 1/2 hour? Plus you need to drive the car a little bit so the computer can learn. I suppose you could try replacing one plug at a time and seeing what happens when you start the engine. It almost sounds like your coil pack wasn't on correctly? Just a guess.

I changed my plugs at 122K, no comments please from the peanut gallery:x, and the gaps were about .045ish on the old plugs. Cleaned my throttle body (now a yearly event) and the car runs better than ever, seems to run smoother and idles better.
 

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2002 chevy trailblazer_lt
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Great write up, for those changing the spark plugs cleaning the throttle body is a must. Depending if it's dirty of course, might as well do it since it's just removing a couple of bolts and disconnecting some clips. Don't forget to disconnect the battery as well.
 
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