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Discussion Starter · #1 · (Edited)
Whats up,
I am having problems with the 05 Tb. I have changed my spark plugs, cleaned my throttle body and changed 2 coil packs and I am still getting a p0300 error. Also, if I get the rpm's over 2k the ses flashes. I have stopped driving it. It all started when it was pouring down rain and I must have got water in #4. Anyway it idles rough and is sluggish. Any Ideas?
The SES does not stay on, it goes off when I slow down.
 

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2002 chevy trailblazer_ls
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7,255 Posts
It is most definitely a misfire, but it sounds like the PCM cannot target the cylinder. You could try jump the coil pack around to see if you can get a more specific code since you already ruled out the throttle body. It could also be an O2 sensor going bad and forcing the engine to run lean and misfire. But my money is on still having a faulty coil pack.
 

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2002 gmc envoy_sle
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1,380 Posts
Also from reading on here, don't EVER drive the vehicle when the light is flashing (unless you WANT to replace the cat. converter!).
 

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Discussion Starter · #4 ·
Updates

I have swapped the coil packs around and still missing. I put a can of Seafoam in the tank but the SES is on so I am unable to run it thru. Wouldn't the O2 sensor have an error code of its own?
 

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2003 gmc envoy_slt
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7,190 Posts
Check the coil wire connectors. They have been known to crack.
 

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Discussion Starter · #6 ·
What's next

I checked the wires and don't see any visible signs of damage. Is there a way to voltage test them? Like I said, It was pouring down when this started happening so I am inclined to believe it is something to do with that. But I don't know. I am thinking about taking it to a shop to have them look at it, but I'v heard some real horror stories on this site and I don't want that to happen to me. What do you guys think?
 

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2002 olds bravada
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2,369 Posts
pull out the fuel pump relay and starve the engine of fuel. take out the suspected coil pack and the corresponding spark plug and ground it. with the coil pack still connected and the spark plug inside the boot and grounded to the frame ( i used the fender, it worked for me), have someone crank the engine and check for spark. if it gives you a good strong spark, the coil pack is fine. if not, there's your problem. make sure to be safe and never touch the end of the spark plug or anything else thats metal.
 

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2002 gmc envoy_slt
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Any solution to this? I'm getting the P0300 code too and I've cleaned the TB. It ran fine for a 1/2 a day then this morning it's back to SES flashing and P0300 code.
 

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2003 Chevrolet Trailblazer LT EXT
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433 Posts
Sounds like this is a very common issue after plugs/TBody cleaning.
I started to change plugs on my TB and found that I had been sold the wrong plugs (got the v8 plugs). As it was Sunday late I just cleaned the T Body and put the old plugs back in. ...ended up with same miss fire that so many people have and the CEL on. Turned out to be code P0306.
Next day I'm back in with new plugs and still have CEL and this time code P0300 random misfire. Over the next 4 hours I went back and forth between computer and TB checking for problems that others had found. Code P0300 all the time.
Then, I found that there was a wire and a vacuum line under the air box that had been rubbing and had exposed the wires and opened the vacuum line...must have cause a short/vacuum leak. I wrapped all the exposed parts of the harness with electrical tape (and fixed the vacuum line) fired it up... Code p0300 again. I tried moving coils around. Code P0306. Then I took someones suggestion to remove the coil harness plugs one by one until I found the cylinder with the miss. When I pulled the connector from #6 there was no change to the idle, as I had switched coil packs already I was suspecting the coil connector plug was bad. I checked all the wires leading through the harness into number 6 and made sure that the wires are firmly pushed into the plug. What ever I did on this round of attempts worked, because when I fired it up it ran like new. This time on the test drive.....no codes. Hope you find your solution. Patience seems to be the solution on this one.
 

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2002 gmc envoy_slt
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Thanks for your note. I also want everyone to know that I have a loaner PCM. I'm getting mine back tuned on Tuesday. Everything started after I put the loaner in. I'm still going spend time today checking everything.
 

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2002 gmc envoy_slt
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I found my problem with the rough idle and the P0300 misfire code. #1 Coil pack was bad.

I "tested" each coil pack by removing the connector while it was on. If there was a change in the rumble/shake then that one wasn't it. If there was no change then that one was it.

Anyway, this is the second one I've replaced. I'm going to replace last four, b/c I don't want to have this problem on a long trip.

I hope this fix lasts longer than the 1/2 day throttle body clean fix. :) I still find it ironic that this started immediately after I installed the loaner PCM. Not saying it caused it, but made it difficult to diagnose, b/c I always had it in my head that the loaner PCM was at fault. :crazy:
 

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2006 chevy trailblazer_ls
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301 Posts
just wanted to say thank you for posting this thread. i've been having the same problem recently and also did a few fixes come to find out tonight after reading this i have a shot coil. going to get one tomorrow if i can find one at the local shop hopefully it fixes everything.
 

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2002 gmc envoy_slt
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just wanted to say thank you for posting this thread. i've been having the same problem recently and also did a few fixes come to find out tonight after reading this i have a shot coil. going to get one tomorrow if i can find one at the local shop hopefully it fixes everything.
Let me know how it turns out. What coil is bad?
 

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2002 gmc envoy_slt
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if im not mistaken its coil 1. the one that is closest to the firewall. and of course i shall you guys the outcome tomorrow.:thumbsup:
OK, cool. Just fyi...1 is closest to the radiator and 6 is the one closest to the windshield. Check and see if you have any corrosion that could indicate water laying on it. I've heard there are leaks from the cowl and it drips on the coil. :undecided
 

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2006 chevy trailblazer_ls
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301 Posts
well the spring looks perfect but the little metal bar the spring connects to is a little corroted but not much at all pluss thats inside the rubber so idk how that happend. lol but around the coil looks pretty good not much corrosion there. but enough to look like that could of been the problem.
 

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2006 chevy trailblazer_ls
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preciate it. hopefully this will do it even though it did turn out to be a good excuse to clean the trottle body, CAI filter, and run some seafoam through it. lol:woohoo:
 

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2006 chevy trailblazer_ls
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ok well heres my follow up...

glad to report every thing is working fine now. i had a P0300 code F.Y.I. turns out i had to replace the spark plugs twice lol. first new set i bought was denso platinum T.T. which seemed to be all burnt up. i finally replaced them with ACDelco plugs which is working fine now. also i had to replace 2 coils and a third one that isnt yet replaced but seems a little dodgy but no problems so far. Cleaned camshaft sensor, crankshaft sensor, Throttle Body, and CAI Filter. also ran 2 bottles of sea foam through the system 1 1/3 bottle in gas tank 1/3 in oil and 1/3 in brake booster. and filled up the coolant since it was throwing a p0128 code.

will run it a bit more and keep my eye on it off to get oil change tomorrow.
as for now every thing is good as new (knock on wood) lol
 
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