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2009 GMC Sierra, misfiring but no codes


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Ctimmerberg
New User

May 8, 2019, 12:44 PM

Post #1 of 7 (338 views)
2009 GMC Sierra, misfiring but no codes Sign In

I have a 2009 Sierra, quad cab 2WD, 5.3L engine with 145,000 miles. About a week ago i began feeling my engine flutter just a bit (maybe 50 rpm spike) between 40-50mph. It became increasingly worse over the next four days. No check engine light or anything unusual. I was in contact with my mechanic and he looked at it for the past two days. My mechanic found that even at idle my truck had a random misfire on all eight cylinders. When driving the truck, the misfire shifts into only cylinders 2-7. The misfire is incredibly small, 20-30 total per minute at about 1000-1500 rpms. He checked for compression issues, valve issues, transmission issues and everything is reading exactly how it should besides the misfires. At this point my mechanic returned my truck with no charge as he can not diagnose any issues. His recommendation was to take it to a dealer or someone who has potentially seen this before. It’s also worth noting in the past four months I’ve replaced the throttle body, all spark plugs, all wired and one coil pack. It also just received a full synthetic oil change within 1000 miles. I’ve only ever ran e85 gas in it. Please if anyone has anything for me, let me know. Me and my mechanic (who i trust greatly) are lost.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

May 8, 2019, 12:48 PM

Post #2 of 7 (333 views)
Re: 2009 GMC Sierra, misfiring but no codes Sign In

You just need a better mechanic



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Ctimmerberg
New User

May 8, 2019, 12:59 PM

Post #3 of 7 (312 views)
Re: 2009 GMC Sierra, misfiring but no codes Sign In

No what i NEED is a little help, maybe someone who has encountered this problem. Not you wasting time with that response.

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Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

May 8, 2019, 1:10 PM

Post #4 of 7 (294 views)
Re: 2009 GMC Sierra, misfiring but no codes Sign In

That is not the way professional techs work. We don't guess or rely on what was wrong with the last car we fixed. We systematically troubleshoot the system to isolate the actual cause and that's what your mechanic needs to do. He first needs to determine whether it's a fuel, spark or compression issue.

You won't find a magic answer on the Internet.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on May 8, 2019, 1:11 PM)


Ctimmerberg
New User

May 8, 2019, 1:19 PM

Post #5 of 7 (288 views)
Re: 2009 GMC Sierra, misfiring but no codes Sign In

Everything he’s tested has been normal. No compression issues, valves are good. Everything. No codes are being tripped and there’s no indication of a bad coil pack or anything like that. We can not isolate the issue...the misfire isn’t saving in the computer history either.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

May 8, 2019, 1:27 PM

Post #6 of 7 (271 views)
Re: 2009 GMC Sierra, misfiring but no codes Sign In

That just proves my point that you need a better mechanic that knows how to run tests to find these issues. One that has a lab scope and knows how to use it. One that knows how to run an injector balance test and scope the primary circuit for the coils and injectors, check for fuel pressure leakage, do a running compression test, etc, etc.

Believe me, good techs know how to find these issues, not your average parts changer down the street.
The scan tool supplies a lot more info than just trouble codes if he knows how to use it.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Double J
Veteran / Moderator
Double J profile image

May 9, 2019, 9:49 PM

Post #7 of 7 (217 views)
Re: 2009 GMC Sierra, misfiring but no codes Sign In

Does this have Active Fuel Management
I'm guessing it does and that may be where your problem is

As Hammertime stated, you need someone who is experienced with this sort of concern
You may be best at the dealer or a different qualified shop

There is a TSB ,(Technical Service Bulletin)for misfires on AFM Vehicles that may apply based on what you describe.
Have your tech look into it
Google Bulletin Number PIP4568S

BTW, Part of the Strategy Based Diagnostics that a Technician does is a Bulletin search






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