2005 Chevrolet 2500 HD 6.0L - Rough Running - P0300 - Engine Misfire
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Customer Complaint: This 2005 Chevrolet 2500 HD with a 6.0L Vortec engine came to the shop with a symptom of running rough and low power.
First Thoughts: I sort of already know what to expect with this vehicle. I have dealt with this issue many times before. Usually, it is something simple like a bad coil or spark plug. But I always get surprised! It could possibly be an injector or something deeper in the engine this time.
Diagnostics: The first thing I want to do with this vehicle is verify the customer's complaint. It is very important to have a feel of what the vehicle is doing when it is acting up.
For this vehicle, it was easy. As soon as I started the engine, it was running rough and had no power. It felt like it was misfiring.
The next thing to do is pull the codes.
Several codes in this vehicle, but I was mainly concerned about P0300. P0300 is set when the engine computer detects multiple misfires. Many General Motors products, like this one, will (sometimes) only give this code rather than a cylinder-specific code. With a cylinder-specific code, it will get us one step closer to the problem, but just a P0300 is a good place to start.
The reason why I was only going after P0300 is that customer did not want to pursue the P1258 or P0332.
The next step is to look at live data.
As you can see in the picture above, cylinders 7 and 8 are misfiring constantly. They also have the most misfires in the history.
Now, it is time to open the hood.
When I opened the hood to take a visual inspection, I heard a distinctive ticking sound.
Cylinder 8 was sparking outside of the engine. I’m willing to bet that is a misfire!
With some more visual inspection, it was found that cylinder 7 had a loose spark plug wire. (It was about to fall off.)
What fixed this vehicle?
New spark plugs and wires were installed on this vehicle and it ran perfectly. Fixed!
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