Engine Misfires - 2015 V8

[glennk]

Carbon buildup?

 

[Genesis5]

I had the exact same issue 6 weeks after purchasing CPO w/~32K miles. Dealer said it was carbon buildup causing cylinder to misfire. $400 and a week later and I was back on the road. Tech said to regularly rev and hold the engine at 5,000 RPM's to burn off any carbon deposits. Been one year and no issues. That's the only issue I've had with the car and I just rolled 40K miles.

 

[V8freak]

I had the exact same issue 6 weeks after purchasing CPO w/~32K miles. Dealer said it was carbon buildup causing cylinder to misfire. $400 and a week later and I was back on the road. Tech said to regularly rev and hold the engine at 5,000 RPM's to burn off any carbon deposits. Been one year and no issues. That's the only issue I've had with the car and I just rolled 40K miles.

Really?! So if I would do that now would it take care of it or do I have to get it cleaned out?

 

[Genesis5]

@V8freak If you're having issues you'll probably want to get it cleaned out. They did the walnut shell blast on mine. No issues for a year, but that's not very long. We'll see if it holds up after 3-5 years.

 

[V8freak]

@V8freak If you're having issues you'll probably want to get it cleaned out. They did the walnut shell blast on mine. No issues for a year, but that's not very long. We'll see if it holds up after 3-5 years.

Ok I might try that! Thanks!

 

[glennk]

From what is being said about VW/Audi Turbo-4's, you'll need a walnut blast every 3 to 4 years depending on mileage.

 

[hamed57]

From what is being said about VW/Audi Turbo-4's, you'll need a walnut blast every 3 to 4 years depending on mileage.

VW/Audi have the worst GDI design in the car industry. No other car is like that.

 

[glennk]

VW/Audi have the worst GDI design in the car industry. No other car is like that.

I really hope you are right. I wish manufacturer's will follow Toyota's lead in modern engine design that has both GDI and Port fuel injection. I asked my dealer about adding a catch can and was explicitly told that will void the warranty on the powertrain.

 

[REMIX]

I have an intermittent problem with a shaky idle like it's going to stall and then a CEL...then it smooths out and goes away. Happened in November and happened again yesterday morning. Ran ok the rest of the day. My OBD scanner says "cylinder 1 misfire". I cleared it, seems ok as of last night. Any ideas? Love the car but it has been something of an occasional pain for various reasons.

 

[V8freak]

I’m not totally familiar with these gas engines… What exactly should be walnut shell blasted? I want to try a can of carbon cleaner that Napa sells but I’m assuming that probably will not take care of it.

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[DSXMachina]

I’m not totally familiar with these gas engines… What exactly should be walnut shell blasted? I want to try a can of carbon cleaner that Napa sells but I’m assuming that probably will not take care of it.

You are correct. If the problem is intake valve deposits then a bottle of miracle juice will NOT have any significant affect whatsoever. This has been documented in independent studies, and can be seen in numerous YouTube videos. When it comes to cleaning deposits from intake ports and valves the stuff is a complete waste of money. I'd suggest Engineering Explained's videos for an intro and overview that sticks to the facts.
I am a member of the Society of Automotive Engineers (SAE), and am an ASE Certified Advanced Level Specialist and Master Auto Technician with 42 years of automotive experience. I have worked on GDI engines and their problems from the beginning. You want to clean intake valve areas you're going to need mechanical abrasion. The most popular method for garages and advanced DIY'ers is blasting with ground walnut shells. That restores the surfaces to factory fresh, but must be done carefully and following the proper procedure.
To answer your question "What exactly should be walnut shell blasted?": It's the portion of the intake valve which is on the intake side (i.e. not the cylinder side) of the cylinder head, and the area around each valve called the intake port. They become so fouled with accreted blowby and crankcase gas condensation that the smooth flow of air is choked off. This air reduction results in a rich mixture which the Powertrain Control Module (PCM) tries to control by the only way it can; it reduces the pulse width to the injector which results in less fuel being injected. Some PCMs are able to identify a specific bad cylinder and just throttle that injector. Others can only do one bank (half the engine) of cylinders as a group. I don't know about the Tau engine.
When the air flow rate is only slightly restricted the computer is able to compensate so the driver feels no difference. At some point the computer can no longer reduce the fuel flow enough without resulting in a misfire. It sets a CEL (Check Engine Light). If the misfire is allowing raw gas (in the form of hydrocarbon vapors) to enter the exhaust, the CEL will flash to try and warn you that you are in danger of melting down your cats.

 

[carguy75]

I have an intermittent problem with a shaky idle like it's going to stall and then a CEL...then it smooths out and goes away. Happened in November and happened again yesterday morning. Ran ok the rest of the day. My OBD scanner says "cylinder 1 misfire". I cleared it, seems ok as of last night. Any ideas? Love the car but it has been something of an occasional pain for various reasons.

What type of fuel do you use? Regular or premium? and what brand?

 

[DSXMachina]

I had the exact same issue 6 weeks after purchasing CPO w/~32K miles. Dealer said it was carbon buildup causing cylinder to misfire. $400 and a week later and I was back on the road. Tech said to regularly rev and hold the engine at 5,000 RPM's to burn off any carbon deposits. Been one year and no issues. That's the only issue I've had with the car and I just rolled 40K miles.

The tech said to "regularly rev and hold the engine at 5000 RPM's to burn off any carbon deposits."? He is wrong on two points. First Your engine should NOT be "regularly" revved to 5000 rpm unless it is in gear. The engine is dynamically balanced to account for crankshaft load. Revving it in neutral vibrates the system in ways not intended. And I don't suggest you rev it to 5000 regularly in gear. You'd be going way too fast. Second, there ain't no way revving it to any rpm is going to affect carbon deposits on the intake valve. I sure hope that tech doesn't think that the air mass at high velocity is going to knock those deposits off...

 

[REMIX]

What type of fuel do you use? Regular or premium? and what brand?

No idea except it's regular. I am in my car all the time and get gas when I need it.

 

[DSXMachina]

No idea except it's regular. I am in my car all the time and get gas when I need it.

I think carguy was alluding to Genesis' strong suggestion that TopTier fuels be used exclusively. TT fuels with their custom blended additive packages have been proven effective at reducing 'gunk' buildup in engines.

 

[V8freak]

You are correct. If the problem is intake valve deposits then a bottle of miracle juice will NOT have any significant affect whatsoever. This has been documented in independent studies, and can be seen in numerous YouTube videos. When it comes to cleaning deposits from intake ports and valves the stuff is a complete waste of money. I'd suggest Engineering Explained's videos for an intro and overview that sticks to the facts.
I am a member of the Society of Automotive Engineers (SAE), and am an ASE Certified Advanced Level Specialist and Master Auto Technician with 42 years of automotive experience. I have worked on GDI engines and their problems from the beginning. You want to clean intake valve areas you're going to need mechanical abrasion. The most popular method for garages and advanced DIY'ers is blasting with ground walnut shells. That restores the surfaces to factory fresh, but must be done carefully and following the proper procedure.
To answer your question "What exactly should be walnut shell blasted?": It's the portion of the intake valve which is on the intake side (i.e. not the cylinder side) of the cylinder head, and the area around each valve called the intake port. They become so fouled with accreted blowby and crankcase gas condensation that the smooth flow of air is choked off. This air reduction results in a rich mixture which the Powertrain Control Module (PCM) tries to control by the only way it can; it reduces the pulse width to the injector which results in less fuel being injected. Some PCMs are able to identify a specific bad cylinder and just throttle that injector. Others can only do one bank (half the engine) of cylinders as a group. I don't know about the Tau engine.
When the air flow rate is only slightly restricted the computer is able to compensate so the driver feels no difference. At some point the computer can no longer reduce the fuel flow enough without resulting in a misfire. It sets a CEL (Check Engine Light). If the misfire is allowing raw gas (in the form of hydrocarbon vapors) to enter the exhaust, the CEL will flash to try and warn you that you are in danger of melting down your cats.

Wow this is so helpful thank you!! It totally explains why my car is doing what it’s doing! I was talking to my mechanic about it this morning and he said they have a chemical cleaning that does the same thing walnut shell blasting would do but before we do that He thought I should try a stronger version of the “crc cleaner” that actually is injected into the fuel line and the car runs off of it during the process. He used it on his car and it made a huge difference. He said at least this way if my problem improves we will know we are on the right track.

 

[carguy75]

No idea except it's regular. I am in my car all the time and get gas when I need it.

I assume that the issue could be from spark plugs that are carbon fouled. The fuel injectors could also be covered by excess carbon. Misfires are usually an ignition issue, so I would check the spark plugs first and then go from there.

I asked about the fuel type because the 5.0 should be using premium fuel in my opinion to reduce the chance of the ECU retarding the engine timing which leaves un-burnt fuel in the combustion chamber which fouls spark plugs and the fuel injectors as well as the valves.

I expect other members to argue that the 5.0 engine does not need to run premium fuel, which is true to a point but I do not think it is best to use regular fuel in the 5.0 engine long term. Maybe every so often, but not as a main fuel source.

 

[Nikhil Malhotra]

Given the v8 engine is so low milage , how could this be related to carbon builtup . Does it not built up slowly overtime . Most of GDI engines need cleaning at 70-100k miles .

Whats missing here . How can a engine misfire at 30 - 40 - 50 k miles ?

 

[carguy75]

Given the v8 engine is so low milage , how could this be related to carbon builtup . Does it not built up slowly overtime . Most of GDI engines need cleaning at 70-100k miles .

Whats missing here . How can a engine misfire at 30 - 40 - 50 k miles ?

I believe that fouled spark plugs is the issue or maybe even a bad coil pack. However, I would inspect the spark plugs first. I bet that the plug tips are covered in carbon deposits.

 

[V8freak]

Definitely a good idea. I’ve got my mechanic scheduled next week to pull out my intake valves and chemically clean them. Sounds like he better check the plugs too while he is in there! Thanks!