2017 Sierra 5.3 Misfire

Jeffc

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Hello, I’m new to the forum. I have a 2017 GMC Sierra 5.3 with 53k miles. I have a sporadic engine miss. I’ve had the fuel induction service and I’ve had all 8 fuel injectors replaced. However the miss continues periodically. I can drive it for 20 - 30 minutes without any issues, then out of the blue it starts to miss for several miles, then clear up again. It will run intermittently with the miss. When the fuel injectors were replaced, it was because the check engine light said that #7 cylinder had a miss. Further diagnostics indicated that the left bank injectors were all bad - so I had all 8 replaced, playing it safe. But now with this latest miss there’s no check engine light. It occurs when the truck is at operating temperature. Without the check engine light on, no one can diagnose it, especially the guys who replaced to fuel injectors. I’ve been fighting this since late December. Does anyone have an idea of what my problem may be? I have not replaced the spark plugs, wire or coils - too much money ($1500 est. for all three items) and I’m over $3k into it now. If I was sure that would fix it, I would have them replaced. Thanks in advance for any input you can provide.
 

Jeffc

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Heard from my repair shop and they have indicated that they were finally able to get my truck to miss while the scanner was connected. Cylinder #7 misfired and it was traced to the coil. They switched the coil with cylinder #5 and the miss followed the coil to #5. So, sounds like my problem was the #7 coil. We will find out for sure when I put miles on it. I hope this will help anyone with this same problem in the future.
 

deepcreekjack

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You can purchase the coils, spark plugs and wires for less than half of that $1500 estimate by purchasing them from rock auto.com. If you can replace the parts yourself, you can save half the cost on parts plus any shop labor to have them changed out. The #8 cylinder plug is a little hard to access, but can be done with the right tools and patience.
 
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