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2002 gmc envoy_slt
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4 Posts
Discussion Starter #1
I initially had a P0301 code, then after switching the ignition coil from cylinder 1 with the coil from cylinder 3, I get P0300 "Random/Multiple Cylinder Misfire Detected".

Is it now safe to assume that the coil from cylinder 1 that is now on cylinder 3 is faulty? And yet another question is that why do I get a Random/Multiple misfire now?

The SES light came on while stopped for gas on a long road trip. I arrived at home and also noticed that there was long gray fibers coming from the tailpipe. I replaced the muffler thinking that was the problem because that is what i was told to do. That did not fix my problem so I got a code reader, which is how I got the initial P0301 code. I then changed the spark plugs, changed the oil and all fluids, and replaced the fuel filter. The P0301 code came back... then the P0300 code... and now here I am.

I have been reading up on similar problems in the forums, but would really appreciate more in-depth advice and/or suggestions. THX ALOT in advance.
 

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8,781 Posts
how does it drive?? have you cleaned your throttle body lately? its gets all sorts of carbon buildup.. (not saying its the problem but its always a good thing to clean it from time to time)


is it rumbling bumbling stumbling?
 

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Western Canada Chapter
2003
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6,411 Posts
Hey Ralphy

If you fill out your profile completely under User CP, it will allow others to jump in and give you some advice. It is helpful to know all the info like mileage and if the SES light was blinking (bad) or on steady?

If you have been driving with a misfire you may have melted the Cat, hence the debris from the exhaust pipe. If you did, then it should be running like a POS. :m2:
 

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2002 gmc envoy_slt
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4 Posts
Discussion Starter #4
to reply to Majestic, yes it is rumbling, bumbling AND stumbling. I will try cleaning the throttle body though, since im sure it needs to be cleaned anyway.

And to blazernut, i have now updated my User CP now, I think I wrote everything needed, I have 140,000 kms (boo canadian! jk). The SES light is on steady when the engine is running, and when i did drive it after my long road trip, it blinked when above 2000 rpms. I haven't drove it since.

I am now going to change the coil from cylinder 1 to see if it helps, and will post the results. Thanks for replying.
 

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2003 chevy trailblazer_ls
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1,708 Posts
how does it drive?? have you cleaned your throttle body lately? its gets all sorts of carbon buildup.. (not saying its the problem but its always a good thing to clean it from time to time)


is it rumbling bumbling stumbling?
:iagree:
The stuff from the tailpipe is the stuffing from the resonator, not really uncommon and you do not really need it anyway.
 

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2002 gmc envoy_slt
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4 Posts
Discussion Starter #6
No more SES light

So I replaced the ignition coil and the light is now gone. No Codes.

Thanks alot everybody! Whooo!
 

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I am having this same problem. P0301 misfire code so I changed all of the spark plugs and changed the ignition coil on cylinder #1. I still have the rough idle and misfire along with the SES light and cyl 1 misfire code. Next up looks like I'll be changing a fuel injector. :(
 

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2002 olds bravada
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2,369 Posts
I am having this same problem. P0301 misfire code so I changed all of the spark plugs and changed the ignition coil on cylinder #1. I still have the rough idle and misfire along with the SES light and cyl 1 misfire code. Next up looks like I'll be changing a fuel injector. :(
might want to run a compression check just in case...
 

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2007 gmc
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159 Posts
Does it also smell rotten or just pig rich?
 

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2004 chevy trailblazer_ls
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5 Posts
I was getting a P0301 code on my 2004 Trailblazer with I6 engine and 102K miles. Idle was rough and acceleration was very sluggish.

After reading this thread and a couple of others pointing the finger at the ignition coil or spark plug, I swapped the #1 and #2 coils and removed and checked both of the plugs. Plugs looked ok so I just put them back in after cleaning.

Took it for a drive and immediately got P0300 code and continued idle and acceleration problem.

Again saw that P0300 (random cylinder misfire) will usually resolve to P030X. So I replaced the original #1 coil with a new one (AutoZone aftermarket unit for $62) and problem was resolved!

I'm just glad it was #1 instead of #6! That one is W-A-Y back there!!

Thanks to all for this great resource on Trailblazer issues.
 

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2003 chevy trailblazer_ltz
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7 Posts
My crappy ordeal

Here's my "F" up. I was swapping my leaky fuel pressure regulator when, while the car was running, inadvertently pulled the pcm fuse instead of the fuel pump relay to relief the pressure in the system. Didn't think anything of it until after the swap. After starting the car it was running very rough and the service engine soon light came on and was blinking. I think I messed up the pcm when that fuse got pulled. Code reade threw out p0300. Since the car is coil on plug and am unable to figure out where the misfire is. All I've done so far is check, clean and regap all the plugs which still looked pretty good. Would rather not buy all six coils at almost $70 a piece to find out that didn't help any. I have heard maybe the crank sensor got messed up by my mishap. ANYTHING I can do to get it back on the road would be a great help. I'm thinking about returning the regulator just in case the new one I just put in happens to be faulty. Although it probably isn't but it has a lifetime warranty so no cost there. not sure if I should buy just one coil and start swapping it from one cylinder to the next and see if I can possibly find a bad coil that way. Running out of options and don't want to replace everything on top of the engine. I think when I pulled that pcm fuse while it was still running I messed up the computer. Only option might be to get anew pcm and then bring it to a dealership to be programmed for however much money. I screwed up big time.
 

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2006 chevy trailblazer_ls
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672 Posts
Here's my "F" up. I was swapping my leaky fuel pressure regulator when, while the car was running, inadvertently pulled the pcm fuse instead of the fuel pump relay to relief the pressure in the system. Didn't think anything of it until after the swap. After starting the car it was running very rough and the service engine soon light came on and was blinking. I think I messed up the pcm when that fuse got pulled. Code reade threw out p0300. Since the car is coil on plug and am unable to figure out where the misfire is. All I've done so far is check, clean and regap all the plugs which still looked pretty good. Would rather not buy all six coils at almost $70 a piece to find out that didn't help any. I have heard maybe the crank sensor got messed up by my mishap. ANYTHING I can do to get it back on the road would be a great help. I'm thinking about returning the regulator just in case the new one I just put in happens to be faulty. Although it probably isn't but it has a lifetime warranty so no cost there. not sure if I should buy just one coil and start swapping it from one cylinder to the next and see if I can possibly find a bad coil that way. Running out of options and don't want to replace everything on top of the engine. I think when I pulled that pcm fuse while it was still running I messed up the computer. Only option might be to get anew pcm and then bring it to a dealership to be programmed for however much money. I screwed up big time.
Easiest and cheapest diagnosis now is to swap coils and see what you get.
 

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2003 chevy trailblazer_ltz
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7 Posts
Bought a spark tester today and found my #3 coil was dead. Bought one and threw it in and car runs nice now and isn't running rough as hell in limp/flashing engine light anymore. I still need to drive it for 50 miles maybe until the computer rechecks everything so I can scan for codes again. stI'll waiting on the computer to check the catalysts and O2 sensors. Idle still fluctuates a bit. Was hoping the fuel pressure regulator would have fixed that. Maybe fuel filter needs replacing??? 81,750 miles. Just sucks there are so many things that can cause it that doesn't throw a code. Hate running things like this down.
 

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2006 saab 9_7x
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450 Posts
Pulling the PCM fuse likely reset it, so now you need to do the throttle body cleaning. Lot's of info on here on the correct way to do it.
 
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