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2004 chevy trailblazer_lt_ext
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Discussion Starter #1
Changed the MAP sensor and no constant misfire on cylinder 4 any more. Now it's down to a P0300. Plugs and coil packs changed 12k miles ago. Any suggestions?
 

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2004 chevy trailblazer_lt_ext
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7 Posts
Discussion Starter #2
Changed the MAP sensor and no constant misfire on cylinder 4 any more. Now it's down to a P0300. Plugs and coil packs changed 12k miles ago. Any suggestions?
UPDATE!!
For 2 days I had the P0300 code and no other and now it's back to a P0304 (Cylinder 4 misfire). I replaced the spark plug in cylinder 4 last week. What is bizarre is that it will misfire for a while and then I will feel the horsepower kick in and no misfiring. It can be during my commute to work of 70 miles where it goes from one state to the other or sometimes it's I drive one time with the misfiring and then the next couple with no misfiring.
Any ideas or suggestions? Is it possible for a coil pack to start failing and cause this or is it as I think that a coil pack either works or doesn't?
 

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2002 chevy trailblazer_lt
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521 Posts
Have you checked other related circuitry like the coil or fuel injector harness connections?
 

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2004 chevy trailblazer_lt_ext
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Discussion Starter #4
I have not checked the coil yet but I did check the other connections. I have a spare coil to try and see if that clears it up.
 

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2004 chevy trailblazer_lt
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484 Posts
Did you replace the spark plugs with ACDelco 41-103 plugs? If not, that could be the source of the problem. These engines are darn particular about which plugs will and won't work right! Also, unless you used ignition coils made/sold by Delphi, ACDelco, or Standard Motor Products/BWD (not T or P series) those could also be a problem. The 6 pack of coils for under $100 sold on ebay or Amazon are highly suspect and lacking in quality.
 

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2006 chevy trailblazer_lt
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I have the same intermittent issue. PO304 - comes and goes. There was a bulletin out related to parking on an incline and rainwater seeping into the #4 cylinder. I used some caulk to try to tighten the seal on the hood. Regardless, replaced the plug and coil and although it got a bit better I still get the random code.
 

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2006 Chevrolet Trailblazer LS
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28 Posts
Had the same issue a few years ago on my 4.2 with #1 spark plug. Wife was parking nose down in the rain and water was accumulating on #1, coming off the windshield, shorting out the system. Fixed it with a new spark plug, lots of dielectric grease and getting her to park nose up.
 

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2006 chevy trailblazer_ls
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Had the same issue a few years ago on my 4.2 with #1 spark plug. Wife was parking nose down in the rain and water was accumulating on #1, coming off the windshield, shorting out the system. Fixed it with a new spark plug, lots of dielectric grease and getting her to park nose up.
GM had a bulletin on the rain water getting into the spark plug wells years ago. The fix was to put a length of weatherstripping under the seal at the back of the hood. I bought the "kit" from a dealer but there was not much to it.
 

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2004 chevy trailblazer_lt_ext
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Discussion Starter #10
Update.......
I replaced the coil pack with the spare I had, pulled the throttle body off and completely cleaned it (There was a bunch of junk on the backside of it probably from the plugged cat I had 7 months ago). No more P03xx codes and it is running much better but after 3 days I now have a P0420 and P0128 code. I had the P0128 come one towards the end of last winter when I had the plugged cat and when I cleared the associated codes from the cat, it never came back on until now. I will replace the thermostat to fix the P0128 but sicne I just replaced the cat within the last year with one from NAPA, is it reasonable to look more towards the O2 sensor now?
 
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