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Random Misfire P0300

cheerdude63

By cheerdude63
in Troubleshooting & Recalls

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cheerdude63 Enthusiast

cheerdude63

Posted
Posted

Hello all, I am new to the site so if this is in the wrong place let me know.  I have a 2015 GMC Sierra, I used the torque pro app to confirm that cylinders 1-4 are recording a misfire under load.  It doesn't miss at idle or at cruise speeds.  Is there something that links all 4 of these cylinders together in the engine harness, like a common ground or something like that.   One more thing, I don't think it matters but, the engine is supercharged with a Magnuson TVS 1900, it has also had the DOD deleted out of the ECM.  Any help would be awesome, thanks.  

Hillwood Enthusiast

Hillwood

Posted
Posted

If only misfires under load I would start with looking at the plugs and wires. If it was a wire or ground issue it should be misfiring all the time,  not just under load.. 

1-3-5-7 are driver's side

2-4-6-8  passenger side. 

If you have 1-4 like you said, then those would be the front two on each side. 

1SLOW1500 Senior Enthusiast

1SLOW1500

Posted
Posted

Oh where to start. I would swap spark plugs and wires out. There should be a Ngk colder plug in there and at least ac delco performance red wires. Then I would remove intake and check for debris. Those kits allow blow by back to intake. 

What catch can do you have? I ask because next question is o2 and afr. But without a data log of a run hard to just pick the issue. 

cheerdude63 Enthusiast

cheerdude63

Posted
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Posted
3 hours ago, Hillwood said:

If only misfires under load I would start with looking at the plugs and wires. If it was a wire or ground issue it should be misfiring all the time,  not just under load.. 

1-3-5-7 are driver's side

2-4-6-8  passenger side. 

If you have 1-4 like you said, then those would be the front two on each side. 

The scan tool I have is only picking up 1-4 or yes the front 4 cylinders. I can, with some certainty, move on a from a common ground issue then.  It is only under load. Thanks.

1 hour ago, 1SLOW1500 said:

Oh where to start. I would swap spark plugs and wires out. There should be a Ngk colder plug in there and at least ac delco performance red wires. Then I would remove intake and check for debris. Those kits allow blow by back to intake. 

What catch can do you have? I ask because next question is o2 and afr. But without a data log of a run hard to just pick the issue. 

I will be doing what you suggest today.  I am not sure what plugs are in it.  I just got the truck and have put just over 1000 miles on it.  The supercharger was installed by Davenport Motorsports in Calgary, AB. I know it does have MSD wires on it.  With all this info you guys have given me,  I am relived that is not mechanical, that was my assumption.  Now I just got to go figure it out, thanks. 

cheerdude63 Enthusiast

cheerdude63

Posted
  • Author
Posted

Hey guys thanks for the help, I did figure it out.  It had 2 bad wires and and an arching coil on #8.  I have since done a complete tune up with one step colder plugs and new coils all around.  I did end up having it tuned this week by Stromberger Performance in Spokane, WA and HOLY #$%^! what a difference that made.  Thanks for the help again.

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