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2003 chevy trailblazer_ls
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Discussion Starter #1
I have an 03 Trailblazer LS with 107,000 miles on it and yesterday one of the cylinders starts misfiring (blinking "Service engine soon" light). The truck struggles to idle properly and there is obvious hesitation during acceleration. This seems to start after it's been running for about 5 minutes, and comes and goes periodically from then on. My Scan guide shows and error code of P0306 which is a Cylinder 6 Misfire. I replaced my spark plugs at 100,000 miles and was wondering if anyone had any ideas on what could be causing the misfire. Please help!!!

Thanks!
Mike
 

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2004 gmc envoy_slt_xl
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plug did not seat right and worked its way loose ..
Loose coilpack
Loose wire going to coil

I take it you checked the gap
 

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Basic Vendor- Skid Plates
2007 chevy trailblazer_ls
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3,700 Posts
Actually, I was at the dealer the other day getting the G80 in my TB looked at, when a lady in an early TB EXT came in with the same thing... Apparently, there is an updated rear hood seal/wiper cowl, with a thicker seal... Apparently, the seal gets smashed down after awhile and water (particularly from snow melting) gets past it and falls on the #6 coil, causing it to go intermittant and corrode...

The service manager (who I was talking to) said that the new seal is basically the old seal, except with a rubber tube or piece of foam inside the open part of the seal (like doing the door seal mod).

Check for corrosion on the #6 coil (to ground), coil connector, and plug wire attachment... If there is corrosion, just clean it up with some emery cloth, slather a whole bunch of dielectric grease (bulb grease) in all of the connections, and you should be GTG...

Mike
 

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Good Luck

In my 06 envoy i6 I had a misfire on Cylinder 1. The first time it was the coil pack and plug coroded and arking to the block. Now I have 52000 miles on it and I have 70% leak by on cylinder one compression test. GM says I need to replace the whole head and all valves. The engine was tore down yesterday and I am going to take pictures and document what it looks like before they take the valves out of the old head.

I would recommend a pressure test if you have exhuasted your efforts on the plug and coil pack, check those first then pressure test the cylinder.

I am very interested to hear what you find.
 

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2003 chevy trailblazer_ls
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Discussion Starter #6
I don't remember the brand of the plugs, but I got them directly from the dealer.

All of the seals look O.K. when I took everything apart, but maybe that's changed with all the snow and cold weather we've had in Chicago this year.

Has anyone had any issues with their valve cover gasket....I'm wondering if I'm leaking oil into the spark plug well. In any case it looks like I'll be having some "quality time" with my engine this valentines day.

Thanks for the input everyone!!!:thx

P.S. I did set and check the spark plug gap on all the plugs.
 

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No not the gasket

I am not talking about head gasket. I am talking about the valve seat inside the head itself. That requires a cylinder valve pressure test to find that problem. Refer to a thread I saw on here search title head problems or known for blowing heads.

I had the same issue with the misfire, and the pressure test is what found the root of the problem. It is what I believe to be the valve seat in the head. It is a 4000 dollar job and I am going through it right now so like I said good luck.

From what I have heard from the dealer 04 to 06's have this kind of problem with the heads. I will post more later after I look and the valves on my disassembled engine tonight. I will post pictures.
 

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2005 chevy trailblazer_ls_ext
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I don't remember the brand of the plugs, but I got them directly from the dealer.


P.S. I did set and check the spark plug gap on all the plugs.
If you got them from the dealer you should be okay. It's not a bad idea to check the gap, but they are supposed to be pregapped, so you shouldn't have to change them at all.
Don't ask how I know, but it's very easy to mess up these new spark plugs when checking the gap! :D

I tend to agree with what Mike said - it's not unheard for the coils to rust and corrode giving a misfire. They I thought usually it is #4 because of it's position, but I could see #6 doing the same thing.
 

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2002 gmc envoy_sle
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I just had this issue come up last night myself. Same exact diagnosis as mng130 (and I did all the same maintainence at the same mileage) but my problem is with Cylinder 1, according to the code that came up. I don't know the order of the cylinders so I don't really know where to begin. If someone could direct me the correct cylinder I would greatly appreciate it. I'm assuming it the cylinder closest to the fan/grille, but I hate to assume things. Also, I think I did use Bosch plugs so now I'm concerned about that because I didn't know there was something wrong with them. What exactly is the concern with Bosch??? Thanks everyone!!!
 

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2004 chevy trailblazer_lt
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I just had this issue come up last night myself. Same exact diagnosis as mng130 (and I did all the same maintainence at the same mileage) but my problem is with Cylinder 1, according to the code that came up. I don't know the order of the cylinders so I don't really know where to begin. If someone could direct me the correct cylinder I would greatly appreciate it. I'm assuming it the cylinder closest to the fan/grille, but I hate to assume things. Also, I think I did use Bosch plugs so now I'm concerned about that because I didn't know there was something wrong with them. What exactly is the concern with Bosch??? Thanks everyone!!!
The concern with Bosch is that they are not as quality of a part as delcos. It's a reputation they've earned across all of the mechanical forums in general. I would switch out to delcos just to make sure and you might even fix your problem in the process.

Regards,
Keith
 

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2006 chevy trailblazer_ls
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I have the exact same problem just start with mine and Im inMichigan. I had the code ran and it came up as misfire in cylinder 6. ANy and all help would be appreciated, id like to try to fix this myself , so any pics or detailed info on what and where im looking would be so much appreciated guys. Thanks again
 

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2004 gmc
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...I had the code ran and it came up as misfire in cylinder 6....
So, if you read the other posts in this thread, you should change the plugs and inspect the coil pack and wiring for plug 6, and the hood seal for maybe dripping water on it. I haven't seen pictures for this simple job posted, but you might get the Haynes manual. Once you realize there are no plug wires as on older designs, it's really obvious where things are.
 

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So it ended up being an easy fix. It was the ignition coil that attaches to the top of the spark plug. I used a tester to find out that the coil was no creating spark. Cylinder 6 sucks to get to because it's in the back near the firewall. Good luck!!!
 

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just tell people you have stage 2 cams thats all :cool: nahh that does stink thoguh best of luck to all of you for the fix
 

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2006 chevy trailblazer_ls
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Can anyone lead me to the 6th cylinder so i know which one im shooting for to try and check out?
 

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2007 chevy trailblazer_ls
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Missfire??

Just because you just had the plugs changes...doesn't meen it was a good plug. Try simply changing the bad plug and go from there. Keep it simple.

Andrew;)
 

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2003 chevy trailblazer_ls
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Discussion Starter #20
Valve cover gasket

Well I got it all fixed this weekend. It ended up being the valve cover gasket around cylinders 5 and 6 (6 being the worse) had deteriorated and was leaking oil into the spark plug well. I guess eventually there was enough oil to mess with the coil. Got a new gasket and all the spark plug wells cleaned out and she's running great (better then she's run in a while).

Luckily taking the coils off and checking the spark plug wells is pretty easy so anyone having similar issues should be able to check pretty quickly. The bad news is that if it is the valve cover gasket the dealer and a lot of the mechanics I talked to were looking for around 500-600 dollars for the job. Fortunately I have a family friend that was willing to do it for $200, but he said it was a lot of work.
 
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