Cylinder 5 Misfire (P0305) Help!

[Chevyman21]

Hi all, I have a 2018 Silverado with the 5.3L. 

As of this month, at 45,000 miles, I’ve started having a sporadic cylinder 5 misfire. It seems to only occur on cylinder 5, and it’s only occurred thus far twice at highway speeds.

The first time it happened, the MIL came on and flashed a few times for about 30 secs. Then it disappeared, After two drive cycles later on that day, the pending P0305 disappeared from the computer. When the MIL was flashing, the truck felt like it cut power, and was stuttering.

 

That was two weeks ago. Today, the same issue occurred. As of now, the MIL is off, but the code is still pending. I’m expecting the code to disappear again on my drive home from work.

 

With it being this intermittent, it couldn’t be something internal could it? What is the most likely culprit?

 

I’m just concerned because the truck is so new, and low milage that something like this shouldn’t be happening so soon.   

 

From my understanding, this cylinder isn’t AFM, so probably not the lifter?

 

Any advice would be appreciated!

[CamGTP]

I'd lean toward a bad spark plug or wire before internal issues.

 

Either buy a new spark plug or swap cylinder 5 with cylinder 3. If the misfire moves to that cylinder you found the problem. Next step after that would be the wire and then the coil pack.

[Chevyman21]

23 minutes ago, CamGTP said:

I'd lean toward a bad spark plug or wire before internal issues.

 

Either buy a new spark plug or swap cylinder 5 with cylinder 3. If the misfire moves to that cylinder you found the problem. Next step after that would be the wire and then the coil pack.

That's what I was thinking too. I'd hate for it to be an injector or something internal. I will pull the spark plug tomorrow and check the wire. I'll report back with my findings.

[Gutz66]

On 12/18/2020 at 10:11 PM, Chevyman21 said:

That's what I was thinking too. I'd hate for it to be an injector or something internal. I will pull the spark plug tomorrow and check the wire. I'll report back with my findings.

Any updates on your issue?

[Ben S]

Any update on this issue? I am getting the same code and behavior on my 2015 at 90k miles. 

[txmuder]

I had #1 cylinder misfire and after changing all plugs, plug wires and then all ignition coil packs myself and still had misfire took truck to dealership and they told me I had no compression in #1 cylinder and needed new long block. Luckily I had bought a extended warranty after I paid truck off and they covered it all except taxes and stuff like plugs, wires and ignition coils which I had already replaced and they didn't cover new belts, hoses and 1 motor mount. But I did get a new 6.2 with 3 year 100k miles warranty from GM and the warranty also replaced entire rear differential, drive shaft and both axles, all bearing and seals and ring and pinion gears as well. Again I only paid taxes and original diagnostic cost.

 

I currently have 135k miles on my 2015 CC LTZ and almost a entire new drive train. Oh and transmission was replaced under original factory warranty at 97k miles 

Edited June 21, 2021 by txmuder

[Chevyman21]

On 1/20/2021 at 10:15 AM, Gutz66 said:

Any updates on your issue?

Sorry for the long leave of absence. Lots of life transitions! Anyways, the weekend after I made the post, I ended up popping the hood and reseating the ignition coil wire, and the spark plug boot, and finally the fuel injector wire into the connector. I've had thousands of trouble free miles since. I suppose cylinder five just had something loose.

[Ben S]

Good to hear. Turns out, I had a Diablo tube on mine at the time. I had messed with throttle boost, shift pressures and disabled AFM. It was shifting so hard with the misfire code, I reset back to factory tune and then only disabled AFM. Truck has driven great since with no issues as that reset cleared the trouble code. I did buy plugs and wires since I am coming up on 100k miles anyway and I am getting them replaced in the coming weeks.