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2002 GMC Envoy SLE
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Discussion Starter #1
I have a 2002 envoy with 172,000 miles that I bought about 6 months ago. everything was fine until it started to have a miss. Showed P0300. I changed all 6 coils and plugs. Still have P0300 Miss got worse , did a compression test, all tested between 174-185, sprayed starter fluid around base of intake manifold,no change in engine. Pulled upstream O2 sensor,no change. Pulled each coil connector while running and #1 and #4 seem to be the culprits. Swapped coils around and still #1 and #4 Should I now pull injectors and replace or clean them? Any advice or help would be very much appreciated.
 

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I am currently having the same problem. Replaced all spark plugs, coils and fuel filter. Hoping someone has an idea.
 

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2002 GMC Envoy SLE
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9 Posts
Discussion Starter #3
I have a friend with a high dollar scanner coming by tomorrow. I am hoping to nail it down. If I do I will let you know something.
 

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2004 chevy trailblazer_lt
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210 Posts
One thing to try in the meantime would be to add two 20 ounce bottles of Techron Complete Fuel System Cleaner to your gas tanks, then fill up with gas and go for a couple hundred mile drive and see if that helps with the P0300 code. You might be surprised at how well that can work.
 

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2002 GMC Envoy SLE
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Discussion Starter #5
One thing to try in the meantime would be to add two 20 ounce bottles of Techron Complete Fuel System Cleaner to your gas tanks, then fill up with gas and go for a couple hundred mile drive and see if that helps with the P0300 code. You might be surprised at how well that can work.
With the cel flashing????
 

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2002 GMC Envoy SLE
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Discussion Starter #6
I am currently having the same problem. Replaced all spark plugs, coils and fuel filter. Hoping someone has an idea.
Found out no spark on 1 or 4 injectors 1 and 4 also not firing. I am going to replace ECM.
 

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2004 chevy trailblazer_lt
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210 Posts
First, you did not mention in your original post that the CEL was flashing.

Second, are you saying that the #1 and #4 injectors are not getting the signal to open/close?

Three, are you also saying that the #1 and #4 spark plugs are ait culso not firing?

I ask because it could be a case of bad connectors, or one or more broken wires between the injector(s) and ECM and/or spark plug(s) and ECM. You might want to do a little testing with a digital multi-meter before spending $$$ on a replacement ECM and reprogramming.
 

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2004 chevy trailblazer_lt
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winstonoats, with all due respect, please do not have multiple threads going on the same issue. I just saw your post from 2 months ago that Ravalli Surfer answered one month ago and then you responded back 2 days ago.

It gets very confusing trying to assist you when there are multiple threads on what is essentially one topic from you.

Regards & good luck & looking forward in attempting to assist you resolve your problem!
 

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2005 buick rainier
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17 Posts
Found out no spark on 1 or 4 injectors 1 and 4 also not firing. I am going to replace ECM.
That's a lot of parts replacement w/ little to no actual diagnostics done. I under stand DIY guys don't have immediate access to $$ scanners but @ the minimum have some good diagnostic data to use.

So both cylinder # 1 & 4 don't have spark or injector electrical signal? A lot of modern vehicle's PCM will disable injector operation if there isn't spark. If the coils were replaced & there still is no spark the wiring should be checked @ the coil harness connector - 12v power and switching signal on (-) terminal.
 

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2003 gmc envoy_slt_xl
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I have a 2002 envoy with 172,000 miles that I bought about 6 months ago. everything was fine until it started to have a miss. Showed P0300. I changed all 6 coils and plugs. Still have P0300 Miss got worse , did a compression test, all tested between 174-185, sprayed starter fluid around base of intake manifold,no change in engine. Pulled upstream O2 sensor,no change. Pulled each coil connector while running and #1 and #4 seem to be the culprits. Swapped coils around and still #1 and #4 Should I now pull injectors and replace or clean them? Any advice or help would be very much appreciated.
On
I have a 2002 envoy with 172,000 miles that I bought about 6 months ago. everything was fine until it started to have a miss. Showed P0300. I changed all 6 coils and plugs. Still have P0300 Miss got worse , did a compression test, all tested between 174-185, sprayed starter fluid around base of intake manifold,no change in engine. Pulled upstream O2 sensor,no change. Pulled each coil connector while running and #1 and #4 seem to be the culprits. Swapped coils around and still #1 and #4 Should I now pull injectors and replace or clean them? Any advice or help would be very much appreciated.
I have a 04 Envoy 220,xxx same code ... turns out it was the VVT Actulator for me. Runs like a champ again.
 

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2006 chevy trailblazer_lt
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I just had the same code. 111K - FTPK20 Fuel System Cleaner - Comes in a can and a bottle. Bottle went into the tank and I dumped the can into the booster vacuum line. Code has been gone for 200+ miles and truck runs great.
 

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2003 chevy trailblazer_ltz
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I have a 2002 envoy with 172,000 miles that I bought about 6 months ago. everything was fine until it started to have a miss. Showed P0300. I changed all 6 coils and plugs. Still have P0300 Miss got worse , did a compression test, all tested between 174-185, sprayed starter fluid around base of intake manifold,no change in engine. Pulled upstream O2 sensor,no change. Pulled each coil connector while running and #1 and #4 seem to be the culprits. Swapped coils around and still #1 and #4 Should I now pull injectors and replace or clean them? Any advice or help would be very much appreciated.
have you tried clearing the codes and running it for a few hundred miles to reset everything? Maybe the injectors DO need to be cleaned or replaced???
 

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have you tried clearing the codes and running it for a few hundred miles to reset everything? Maybe the injectors DO need to be cleaned or replaced???
I'd try running a gallon or two of Lucas Oil treatment thru it, doubling the recommended amount. It's safe for gas AND diesel. I've got an older Freightliner with 800k, and it's made it sound and run like a different engine.
 

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I have a 2002 envoy with 172,000 miles that I bought about 6 months ago. everything was fine until it started to have a miss. Showed P0300. I changed all 6 coils and plugs. Still have P0300 Miss got worse , did a compression test, all tested between 174-185, sprayed starter fluid around base of intake manifold,no change in engine. Pulled upstream O2 sensor,no change. Pulled each coil connector while running and #1 and #4 seem to be the culprits. Swapped coils around and still #1 and #4 Should I now pull injectors and replace or clean them? Any advice or help would be very much appreciated.
Where did you buy the coils and plugs ? Use the old coils for number 1 and 4 to see if the new coils are bad or defective
 
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