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Go Back   Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum > 2002 - 2009 TrailBlazer/Envoy Tech > 02-09 Vortec 4.2L I-6 Engine and Drivetrain > OEM Issues

OEM Issues Original Equipment Repairs and/or Problems

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  #1  
Old 04-06-2017, 07:28 PM
alexalexanders alexalexanders is offline
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2008 Chevy TrailBlazer LT
Imperial Blue Metallic 4.2L I6 4X4
Join Date: Dec 2015
Location: Springfield'mo
Posts: 3
Misfire need help

Ok here we go. I have a 08 trailblazer with the 4.2 I6. My father in law is a retired gm ase certified tech and has been the only person who has looked at it Heres my misfire problem.I noticed a rough idle last year with no cel light. Figuring it was plugs I ordered 6x 41-103 ac delcos and replaced them. A few months later I got a random misfire code. My father in law hooked up his tech 2 and saw it was cyl 6 that was counting up and the only cylinder with a misfire. Swapped coils and plugs all over and it never changed from number 6. I even for the chance of it put a new ac delco coil on 6 and it didnt change it He diagnosed a bad fuel injector, I ordered all 6 ac delco fuel injectors and ac delco intake manifold gasket. He put them in and noticed the valves covered in carbon build up, and the injectors especially number 6 with carbon build up. The trailblazer ran alot better and the miss was very intermittent.We then used some seafoam spray through the throttle body to break up the carbon on the valves. He suggested using better gas and running a bunch of fuel injector cleaner through it to break up carbon also, which we hadn't been before. I've been running top tier gas and marvel mystery oil through the tank over the last 1,000 miles. My question is I still have the misfire, sometimes runs great sometimes runs extremely rough at lights and take off. Once you come off idle it runs fine driving and looking on the tech 2. Does anyone have any other suggestions or had this happen to them before? He said we could do a head rebuild but he thinks thats a little extreme. Sorry for the long post and thanks for the help!
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  #2  
Old 04-06-2017, 08:40 PM
lightthemup lightthemup is offline
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2003 GMC TrailBlazer LS
Dark Gray Metallic 4.2L I6 4X4
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Did you do a compression test?

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  #3  
Old 04-06-2017, 11:53 PM
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AWD V8 AWD V8 is offline
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2003 GMC Envoy SLT
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^^ yup
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I was planning on procrastinating today but I think I'll do that tomorrow.
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  #4  
Old 04-07-2017, 08:29 AM
Redtblazer Redtblazer is online now
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2002 Chevy TrailBlazer LTZ
Bordeaux Red Metallic 4.2L I6 4X4
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What about the connector and/or wires going to the coil pack?
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  #5  
Old 04-07-2017, 06:51 PM
alexalexanders alexalexanders is offline
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2008 Chevy TrailBlazer LT
Imperial Blue Metallic 4.2L I6 4X4
Join Date: Dec 2015
Location: Springfield'mo
Posts: 3
Quote:
Originally Posted by lightthemup View Post
Did you do a compression test?

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We have not done a compression test. Main reason being as the miss does come and go and isn't constant.

One thing I did do today seafoam it. I sucked roughly about a third of the can through the brake booster line. By the time I got the seafoam sucked it the exhaust was already starting to smoke and could already smell carbon burn off. My father in law is all but convinced of it being a carbon issue, and I'm just looking at all possibilities.

Another thing, I've noticed it more when motor is cold. I was thinking back to when I changed the plugs when I plugged 5 and 6 out the threads were oil soaked, but not the spark plug wells. I asked my father in law about it and he said these were pretty common for valve cover gasket failure and that someone probably changed it and not the plugs and to keep a eye on it. I checked about 1k later and they were try. My question is what are my chances I have a COP boot acting up from age or since they have had oil on them? Or should I change them anyways? BTW the trailblazer has 96k miles on it and the plugs and one coil pack were changed at 87k drove till 95k and then the fuel injectors and intake gasket changed.
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  #6  
Old 04-07-2017, 06:51 PM
alexalexanders alexalexanders is offline
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2008 Chevy TrailBlazer LT
Imperial Blue Metallic 4.2L I6 4X4
Join Date: Dec 2015
Location: Springfield'mo
Posts: 3
Quote:
Originally Posted by Redtblazer View Post
What about the connector and/or wires going to the coil pack?
Seemed ok but will check again
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  #7  
Old 04-20-2017, 05:48 PM
Brbreshears Brbreshears is offline
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2004 GMC Envoy SLT XL
Dark Green Metallic 4.2L I6 4X4
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I have an 04 GMC Envoy. Took to a shop their hand held computer said there was a misfire on cylinder 2. They checked the spark plugs and they said they were good put different coils on no change so the switched them around and still no change. They did say there was some oil around one spark plug but not down inside. Ran some seafoam thru the gas tank didn't help any. So they said might need one maybe 2 injectors. There is no lights on the dash. It bucks when u are driving and when idling it idles ok at times other times it acts like it's missing. The shop wants about 700 or more depending on what is wrong. Is there anyway to know what's causing it without changing this and that? Has anyone else had this problem
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