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2002 chevy trailblazer_lt
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55 Posts
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?
Maybe. We need more info. Why were you removing the coil packs? Was the engine misfiring? Did it overheat? Which cylinders had oil?

It could be just from a spill. It could be a problem with the valve cover. It could be worse. More info, and maybe pics would be helpful.
 

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2005 chevy trailblazer_lt
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Maybe. We need more info. Why were you removing the coil packs? Was the engine misfiring? Did it overheat? Which cylinders had oil?

It could be just from a spill. It could be a problem with the valve cover. It could be worse. More info, and maybe pics would be helpful.
i was changing the spark plugs. all the cylinders had some oil in them but the first (closest to the front) had the most by far
 

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2002 chevy trailblazer_lt
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i was changing the spark plugs. all the cylinders had some oil in them but the first (closest to the front) had the most by far
Tell us more. What did the plugs look like? Were the coil boots covered in oil? Was the oil black, grimy, fresh looking? Any signs of leaks anywhere? Antifreeze color okay?
 

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2005 chevy trailblazer_lt
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Tell us more. What did the plugs look like? Were the coil boots covered in oil? Was the oil black, grimy, fresh looking? Any signs of leaks anywhere? Antifreeze color okay?
yea the coil boots were covered in oil. Having just changed the oil a few weeks ago it appeared fresh. I didnt notice any leaks from any place. the plugs themselves were in rough shape. but we new that was going to be the case as they had never been replaced before and there was a serious misfire (thats why we were changing them.)

Basically, wanting to know if i change the valve cover gasket will that take care of whatever leak caused this
 

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2005 chevy trailblazer_ls_ext
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Changed my plugs

Thanks for all the great insight here! I had found a video on YouTube that got me started, but I was about to give up on plugs 5 & 6 on my 2005 TB EXT withe the L6. Then I found this forum!

It was a piece of cake except that the foam insert in my socket came out of the socket and stayed on #5 plug. Had to remove the plug, fiddle with the foam and then no more trouble!

It already sounds better! Getting ready to road test it in a bit!
 

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2002 chevy trailblazer_lt
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It was a piece of cake except that the foam insert in my socket came out of the socket and stayed on #5 plug.
Happens all the time with those sockets. If the plug doesn't seat right after a change or there is a misfire, look inside your socket to see if the plug holder is still in there (usually on the last plug changed; other plugs you notice it right away when you go to pull the next plug). I have 3 sockets for plugs (two sizes), and they all have had this happen.
 

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2003 chevy trailblazer_lt_ext
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I have a 2003 Trailblazer EXT with 209,000 miles on it. I have changed the plugs twice every 100,000 miles with no problems. The other day it started running rough and was getting a flashing "Check Engine Soon" light. I ended up finding the #6 coil pack not seated on the plug because the hole for the retaining bolt is stripped out.

I assume the retaining bolt threads into the head. Can anyone tell me if there is an insert or helicoil that goes into it or is the head actually threaded. If anyone can help with any other solutions, it is greatly appreciated.
 

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2005 chevy trailblazer_ls_ext
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Still runs rough

After changing plugs, I find it still runs rough and I have a flashing check engine light indicating a misfire.

Anyone know if the diagnostics that auto parts places like Autozone does will tell me which cylinder is misfiring?

I plan on pulling the coil packs one at a time to make sure the boots are seated.

Plugs 1 - 3 all had oil all around them and some on the boots, so I guess I need a valve cover gasket.

Will oil damage the coil packs to cause a misfire? None looked especially bad, but coil packs are new to me.
 

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2006 gmc envoy_sle_xl
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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.
Mine is doing the same thing now? How did you fix it
 

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2002 gmc envoy_slt
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Thanks

Thank You so much, you have shown me that there really is an engine under all those big black plastic covers! :hail:

I have saved your PowerPoint, explains it much better than what Chilton now call guides.
 

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2002 chevy trailblazer_lt_ext
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My wife drives our 02 Envoy XL. She said it wasn't starting right up like it usually does and the check engine like had come on. I took it to Advance Auto and had them run the code- misfire on cylinder 4. I ran a couple of bottles of fuel injector cleaner in the gas thinking it was maybe bad gas or a clogged fuel injector. That didn't seem to help, so I figured I would change the spark plug and check the wire to cylinder 4.
I am used to working on older cars. When I went to locate the spark plugs and wires I couldn't even find them. I was about to call a mechanic when I decided to check this forum, since I have gotten so much info for the lift on my Trailblazer.
One of the posts said something about #4 being the usual culprit. I picked up an ignition coil at Advance Auto for $65 and swapped #4 out following the first post as a guide. It helped out a lot even though I didn't know what the "air resonator" was until I opened the hood and used context clues. I was not able to open the google doc to see pictures.
Thanks to Megeler for the detailed instructions and to those who posted after with other tips and helpful information!
I have the battery cable unhooked to see if that clears the check engine light. It sounded like that is what I am supposed to do. When I started the Envoy up it ran smoothly, much better than when I parked it in the garage the day before.:woohoo:
 

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2005 chevy trailblazer_ls
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160 Posts
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.
How do you determine which cylinder is misfiring ? Does the OBD2 tell me that ?
 

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2005 isuzu ascender
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4 Posts
so I broke something...

Whats the little brittle tube that is connected to this thingy for? mine just literally broke into four pieces as I was working around it...

James
 

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2009 chevy trailblazer_ltz
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Holy crap I succesfully changed spark plugs!

Just wanted everyone to know I changed spark plugs for the first time in my life, in large part due to the encouragement of this forum.

Couple things I experienced:

I have a 2009 Trailblazer with about 70,000 miles.

Super easy to change the plugs the only hang up I had was my spark plug socket kept getting stuck on the new plugs after installing, so I'd come back with needle nose to pull the socket off.

I didn't think there would be enough clearance for the needle nose pliers on the plug furthest into the engine bay so for that plug I removed the rubber boot on the socket. I placed the plug into the cylinder with my hand and then gently screwed it in with the bootless spark plug socket.

All the old plugs felt overly tight to me coming out, and they all made creaking noises(but I've never done this before so who knows). But, because I was scared to death of breaking a spark plug I was super slow and steady removing them.

I placed anti-seize on the new plugs and used a torque wrench (noob I know).

The engine was really smooth before and now feels even smoother :)

Oh, and I tried to take off the throttle body to clean it while I was at it, but couldn't figure out the gad dang electrical plug, so I just sprayed cleaner on a rag and cleaned it from the outside best I could.
 

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2005 isuzu ascender
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319 Posts
Congrats, good for you.

Nothing wrong with using a torque wrench. Only way to ensure you get things back in spec.
 

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2003 chevy trailblazer_ltz
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210 Posts
I was going to start a new thread, but a search turned up this thread, and much of what I was going to cover would be a repeat of what's already been posted.

I have some quibbles about the First Post. It's working for people, but there are some minor mistakes. My comments on the Tools/Items Needed section:
1. Different folks will use different tools.
2. A tube of silicone dielectric grease is recommended--I use a dab to lube the end of each of the rubber plug boots.
3. I also used a bit of aerosol carburetor cleaner, and a round wire brush with a diameter just larger than the spark-plug threads. I got mine in the Plumbing section of the hardware store, sold for cleaning copper tube before soldering.
4. I suggest "Steel Reserve" also known as "211", (although strictly speaking it's an alchemy symbol not a number) as the beer of choice.


Step 1:
Remove the Air Resonator by undoing 2 - 10mm bolts on the right hand side, loosening the clamp around the air intake tube to the left of the mass air flow sensor, and the clamp where the air resonator joins the throttle body. (Left and right on a vehicle are based on the position of the driver, behind the steering wheel.) Be sure to detach the mass air flow sensor wire from the resonator by undoing the plastic clip.
Also remove two hoses, one approximately 1/2" hose from under the left front, and one small plastic hose with rubber boot from right front side.

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. My engine had some dead leaves tucked under the wire harnesses for the coil packs. A blast of compressed air removed all loose debris. 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. As soon as the coil pack is removed, I paint the hold-down bolt threads with a light coat of anti-seize, and smear a little bit of silicone dielectric grease inside the rubber boot using my little finger. It's sort of like freshman-year sex.
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. I remove carbon on the spark plug hole threads and around the tapered seating area of the cylinder head using a few light sprays of aerosol carb cleaner and the round wire brush. (Don't "thread" the brush very far into the plug hole. I brushed AROUND the hole, removing carbon from the tapered-seat area.) The dissolved carbon and carb cleaner will drain into the cylinder, but better there than having grit between the taper of the plug seat or plug threads, and the cylinder head. A blast of compressed air will remove some but not all of the carb cleaner and dissolved carbon. The engine may smoke for a couple of seconds when started. I had to do this on the rear two plugs without looking down inside, I'm glad I worked front-to-back so I could see results on four of the six cylinders. 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. I paint the threads with a thin coating of anti-seize including the taper that the plug seals to the head. 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. Or use a trustworthy torque wrench set to 13 ft/lbs or 156 inch/pounds. Now reinsert the coil pack being sure the spark plug boot 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. Also re-connect small plastic tube with rubber boot to nipple on resonator.

...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.
Unlike the original poster, I purchased replacement spark plugs at 90K miles. I pulled all the original plugs out--and each one looked SO PERFECT that I tightened the gaps about .002 or .003 to get back to .040, applied anti-seize to them and screwed them right back in, even though the brand-new ones were sitting on the fender. The original plugs came out with a terrifying amount of initial torque, and a "snap" from the ratchet when they broke free, but without any damage and they turned easily once they had that bit of initial movement. I don't think GM follows their own torque recommendations!

It's now several years later, my TB has 165K on it, shows no codes, and runs great. However, My Bride is taking this vehicle on a trip to Alaska with her Mom and Step-Father; so it's getting spark plugs, tires, sway bar links, brakes, etc. before she leaves, 'cause if she has problems she'll fly home on her temper.

I probably have some oil seepage from the valve cover into a couple of the spark plug cavities in the cylinder head. I didn't see any oil on the plug boots, but the bottom of the plug shells and the plug threads on a couple of plugs had some oil.

The plugs came out easily, no terrifying torque or "snap"; I'm a FIRM believer in anti-seize when steel (the plug shell in this case) is screwed into aluminum.





 

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2003 gmc envoy_slt
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For those experiencing rough running immediately after changing spark plugs, two things I'd recommend checking. First, once you screw each new plug in, clean the top of the spark plug head with your finger or a towel, then clean around the boot of the coil pack before putting it on. If you get any oil on the top of the plug (say from a slightly leaking valve cover gasket), the plug may not fire properly. Secondly, put some diaelectric grease on the contacts inside coil pack boot before seating it on the new plug. It costs about $1.40 for a packet of sparkplug grease. That should give you a solid electrical connection.

Just finished changing my spark plugs - I had a power loss at low speeds that suddenly developed yesterday, accompanied with a significant drop in gas mileage. The car didn't throw any codes, but was very sluggish, particularly off the line. It felt like I lost a cylinder or something. Today, I cleaned the throttle body, replaced the air filter, tested the coil packs (all were good) and then replaced all 6 spark plugs. That cured the problem! Don't know which of the three was the culprit, but don't really care. The plugs looked like they'd never been replaced on the car, so I suspect one of them may have finally given up the ghost. Going forward, I'm planning to change them every 75K miles.

The furthest plug wasn't the nightmare I was expecting. I used a breaker bar with light pressure to remove the old plugs. It gave me a long reach and made it pretty easy to deal with the seized plugs. I'm sure I would have been cursing a lot if I'd just used a 3/8ths ratchet. In retrospect, I should have sprayed a little PB Blaster in there to unfreeze the metal before removing them. I put anti-seize (high temperature, designed for sparkplugs) on the top 1/4 of the threads when I installed the new plugs. Plug 1 was the biggest PITA, thanks to the wire channel and the idiotic clips they use to hold it in place.
 

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2002 chevy trailblazer_ltz
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Always needing help....

Temp seems to always be an issue with these. Runs 210 - 230 which is kind of in normal range. But But I would like it below 210 all of the time. Live in Florida and the summer temp is above 90 every day. Have already replaced the thermostat and temp sending unit. Gauge seems fairly accurate according to the computer reading. Has 179,500 on the L6 and still has a great deal of the 275 hp it was born with..Just for fun going to replace the electronic fan clutch which is terrible and they go out all of the time. Easy to change. Also thinking of a special made radiator. A 3 or 4 core staggered configuration they we used to put on our 700 hp 350 cid in high school. And that was many years ago but we have a great radiator company who can make anything. Any thoughts from anyone. Thanks Ron
 
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