Excessive Carbon Build Up / Misfire

[dish]

I just had to take my truck in because it was misfiring.

I’ve got a 2021 Silverado/Sierra with the 5.3 and 10-speed, just rolled 100k miles. First time I brought it in, they suspected carbon buildup. They ran a cleaner through it and gave it back. About 5k miles later, same issue again. They ran the cleaner again, said it wasn’t uncommon to need more than one treatment—but it still didn’t solve it.

At that point they pulled the intake to check the valves. Turns out there was way more carbon buildup than expected, even after two cleanings. The tech referenced Bulletin No.: 16-NA-383 and said my valves had about double the carbon compared to the “before” pictures in that bulletin.

Their recommendation now is to walnut blast the valves, which should remove 95% of the carbon. That’s fine short-term, but it doesn’t address how the carbon got there. I know oil consumption is common on these engines, mine just gave me a low oil warning right as I was due for a change (7–8k miles after the last one). So both me and the tech are assuming oil consumption is what caused the buildup.

So now I’m trying to figure out the best path forward. The way I see it:
1) Clean it and drive it - Add oil when needed, run top-tier fuel, monitor the carbon buildup.
2) Address oil consumption – Worst case I’m into pistons and rings, which is $$$.
3) Trade it in – Don’t really want to because I like the truck, but it’s an option.

I’ve also been considering an AFM delete—does that actually help with oil consumption? Any downsides?

Would love to hear what others have experienced or what you’d do in this situation.

 

[2KWIK2C]

Drive it like you stole it is the only thing I have to offer. I never had issues with mine!

 

[mrcolieman]

As 2WKIK says above. Also don't wait so long to change your oil. I change mine every 5k miles max. The older the oil gets the more byproducts of combustion it has contaminating it which means more available carbon to be deposited on the back of your valves through the PCV system. Modern direct injected engines don't have any fuel going through the intake and past the valves so top tier fuel won't make a whole lot of difference in keeping the valves clean, but is always a good idea and it will keep your fuel system and injectors cleaner.

Maybe educate yourself on a catch can. Some people swear by them. I haven't seen enough evidence that they make a difference on our V8s to put one on my truck. But no judging! If it makes you feel better go for it.

AFM/DFM delete might help with oil consumption, but...
I've read an opinion that these engines use oil more because with AFM/DFM active and both valves closed on the down stroke of the piston, such great suction is produced that it pulls oil past the rings and into the cylinder which is then burned next time that cylinder fires up again. I'm no engineer so someone smarter please speak up if I got that wrong. It would be an expensive option and unless you were after other performance and reliability benefits I think save that money and keep it for a low mileage used engine to get another 100k miles out of?

Sometimes I wish it was simple as going back to my '75 K10 Cheyenne, but then I remember I only got 80K miles out of that 350 and felt pretty good about it. Our modern trucks are amazing and I do love mine. I'll put another engine (or two) in someday if needed...

Best of luck,
CJ

 

[dish]

As 2WKIK says above. Also don't wait so long to change your oil. I change mine every 5k miles max. The older the oil gets the more byproducts of combustion it has contaminating it which means more available carbon to be deposited on the back of your valves through the PCV system. Modern direct injected engines don't have any fuel going through the intake and past the valves so top tier fuel won't make a whole lot of difference in keeping the valves clean, but is always a good idea and it will keep your fuel system and injectors cleaner.

Maybe educate yourself on a catch can. Some people swear by them. I haven't seen enough evidence that they make a difference on our V8s to put one on my truck. But no judging! If it makes you feel better go for it.

AFM/DFM delete might help with oil consumption, but...
I've read an opinion that these engines use oil more because with AFM/DFM active and both valves closed on the down stroke of the piston, such great suction is produced that it pulls oil past the rings and into the cylinder which is then burned next time that cylinder fires up again. I'm no engineer so someone smarter please speak up if I got that wrong. It would be an expensive option and unless you were after other performance and reliability benefits I think save that money and keep it for a low mileage used engine to get another 100k miles out of?

Sometimes I wish it was simple as going back to my '75 K10 Cheyenne, but then I remember I only got 80K miles out of that 350 and felt pretty good about it. Our modern trucks are amazing and I do love mine. I'll put another engine (or two) in someday if needed...

Best of luck,
CJ

Appreciate your thoughts and the time you took for your response.

Definitely no silver bullet. I have a friend with a 5.0 f150 that swears by his catch can but haven't heard too much about it on 5.3s. I definitely go easy on my engine, maybe I need to be more spirited in my driving here and there! haha

 

[Yak]

I just had to take my truck in because it was misfiring.

I’ve got a 2021 Silverado/Sierra with the 5.3 and 10-speed, just rolled 100k miles. First time I brought it in, they suspected carbon buildup. They ran a cleaner through it and gave it back. About 5k miles later, same issue again. They ran the cleaner again, said it wasn’t uncommon to need more than one treatment—but it still didn’t solve it.

At that point they pulled the intake to check the valves. Turns out there was way more carbon buildup than expected, even after two cleanings. The tech referenced Bulletin No.: 16-NA-383 and said my valves had about double the carbon compared to the “before” pictures in that bulletin.

Their recommendation now is to walnut blast the valves, which should remove 95% of the carbon. That’s fine short-term, but it doesn’t address how the carbon got there. I know oil consumption is common on these engines, mine just gave me a low oil warning right as I was due for a change (7–8k miles after the last one). So both me and the tech are assuming oil consumption is what caused the buildup.

So now I’m trying to figure out the best path forward. The way I see it:
1) Clean it and drive it - Add oil when needed, run top-tier fuel, monitor the carbon buildup.
2) Address oil consumption – Worst case I’m into pistons and rings, which is $$$.
3) Trade it in – Don’t really want to because I like the truck, but it’s an option.

I’ve also been considering an AFM delete—does that actually help with oil consumption? Any downsides?

Would love to hear what others have experienced or what you’d do in this situation.

If your true boss has a digital fuel management system, it’s recommended that you run a fuel additive at least once a month. When I bought my 2022 Chevy trail boss it was right after Covid and there was a chip shortage so my truck did not come with the digital fuel management system. When I bought the truck, I was kind of bummed that it did not have the digital fuel management system. But now I am so so glad my truck doesn’t have the DFM.

 

[Stormin08]

it would have been sweet if it were a hard part shortage and GM went with better internals

not having the CHIP is one thing, i would rather not have the valvetrain

 

[Yak]

it would have been sweet if it were a hard part shortage and GM went with better internals

not having the CHIP is one thing, i would rather not have the valvetrain

I think the reason valves are having excessive buildup from being deactivated while the truck is running.

 

[Stormin08]

GM has roughly 17-19 varying firing orders for these engines...don think it just shuts 4 off and leaves them for any length of time.

typically, the service records usually show lack of maintenance, or extended intervals...

 

[Jes]

Checkout Lake Speed Jr on YouTube. I am starting to use Techron monthly and switching to Valvoline restore and protect 5w30…
I am at 64000 and my 5.3 was built without the DFM chip.

 

[Yak]

Checkout Lake Speed Jr on YouTube. I am starting to use Techron monthly and switching to Valvoline restore and protect 5w30…
I am at 64000 and my 5.3 was built without the DFM chip.

Same here no DFM I was thinking about using the Techron also how’s it working for you? I am at 62000k. Chevron Techron fuel additive fuel system cleaner?

 

[Stormin08]

you CAN just buy chevron fuel....although slightly less concentrated, it is easier to hit the pump than add a stop

just sun a bottle once every few months to help cleanup the remnants