Codes P0308 and P219B, cylinder 8 misfiring continuously?

2015 GMC SIERRA
138,000 MILES • 6.2L • V8 • 4WD • AUTOMATIC
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TYJACK12345321
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I posted a forum about a month ago of a ticking sound coming from my engine. I took it to my dealership, and they fixed the issue. They replaced the injectors and seals.
Everything was great! Until now...

Yesterday I started my truck, and my check engine light was blinking, and the traction control symbol popped up. My engine began to shake. You could feel the misfire from the driver's seat. As soon as you put it in gear, it shifts hard, and the light will turn solid and it will drive normal. You can tell there is a loss in power and hesitation. I scanned it with a tool, and I got the code P0308 and P219B. The first thing my buddy and I looked for was disconnected spark plug wires and we found nothing wrong. I went to the parts store to get spark plugs and they only had 4. So, we replaced the left side plugs and plan to replace the other side today. We are going to replace the wires as well. If that doesn't fix the issue. Does anyone have any recommendations?
Oct 3, 2022 at 10:16 AM
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STRAILER
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The code P0308 is a misfire on #8 which is usually a cracked spark plug because it is tough to get to and easily cracked. Also, did you use AC Delco parts? The P219B code is a mixture issue which should go away once the plug is replaced, clear the codes when completed. Let me know how it goes.
Oct 3, 2022 at 5:42 PM
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TYJACK12345321
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I already replaced the plug on that cylinder and there was no change. I also moved coil packs with no improvement. We hooked it up to the scanner and the injector for cylinder 8 wasn’t running the same as the others so we believe that’s the issue.
Oct 3, 2022 at 5:59 PM
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STRAILER
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Yep, that was going to be my next suggestion. here is how to change it out, I would use AC Delco parts. Check out the images (below). Please let us know what happens.
Oct 4, 2022 at 2:19 PM
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TYJACK12345321
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Update. I replaced all the injectors on that side and it’s still not fixed.
Oct 8, 2022 at 1:21 PM
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Okay, the next thing we need to do is check compression here is a guide to help. I didn't think this would be an issue on this new of a truck, but you never know.

Here is a guide to help:

https://www.2carpros.com/articles/how-to-test-engine-compression


Please go over this guide and report back. Also, can you upload an image of the start plug when you remove it, please?



Oct 10, 2022 at 9:57 AM
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TYJACK12345321
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i am having the same issue and ive done these steps and i am stuck after the compression test
Dec 12, 2025 at 8:30 AM
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So did you do the compression test? What are you stuck on exactly?
Dec 12, 2025 at 8:31 AM