I have a 2016 Sonata hybrid. I spent many months dealing with spark plug misfires. In March my mechanic did a carbon cleaning and that made the problem go away. Unfortunately, today (5 months later) it came back. I got a check engine light and when I checked the code it was a misfire again. Specifically, it was a misfire on cylinder 2 (which is where it always is). I cleared the code and drove the car some more and it didn’t (yet) come back. But, based on the history of this car, my guess is that it will come back and eventually get to the point where it does not go away without some kind of intervention. Two things did happen to the car recently before the misfire. They’re probably not related, but I thought I should mention them. (1) Four days ago my transmission fluid, brake fluid, and coolant were all changed by my mechanic. Not because anything was wrong - just because I’m trying to avoid problems by keeping up with regular maintenance. (2) Two days ago I put gas in my car and for the first time I used Lucas Upper Cylinder Lubricant. I’m concerned that I’m going to start having major problems with this car again. Is there something that I can do that might help me to keep these misfires from coming back?
I’ve used this product for many years to remove carbon deposits from intake runners/valves with great success.
Tester
Could be the gas you bought, and or the additive… How often are you adding additives to the fuel tank and or engine oil??
This was discussed in the thread above and possibly one or two other threads…
Still unanswered questions from the above thread…
Either you (or shop) are installing the wrong spark plugs, which I covered in prior post, or counterfeit and or non dealer parts, or you possibly have an electrical issue…
Maybe your buying cheap gas???
Might be time to find an automotive electrical specialty shop…
Thank you.
I am currently using the correct spark plugs. I get exclusively get my gas at Costco. Is Lucas Upper Cylinder Lubricant not a good choice?
Hopefully from the dealer??
Costco should be fine, might switch to Shell just to see if you have any better luck..
Typically additives are not needed and can cause issues like build up on the valves and combustion chamber area…
If you are running good fuel and doing proper maintenance to the vehicle, you should not need to use additives…
Using a cleaner such as Sea Foam (tank) or Marvel Mystery Oil (oil or tank) or equivalent are needed, but MMO is more for sludge and heavy deposits, whereas Sea Foam seems to work great in the tank for decarbonizing the induction side… Always follow directions for either…
The next time the cylinder 2 misfire comes back, try switching the number 2 coil pack with another cylinder and see if the code follows that coil pack. I seem to remember reading that on your vehicle there was a problem with owners of your vehicle were going to the dealer for misfire codes and the dealer was changing the coil packs under the vehicle warranty. Your 10-year 100k mile warranty might have expired
Is your car burning oil? On our non hybrid with the Theta II engine, the oil burning was horrible and then the spark plugs started fouling before the engine seized and was changed under the class action lawsuit.
Even on a 2016 Hyundai/Kia GDI engine?
If I owned this car it would get an induction service every 30K, based on what I’ve seen in the field.
I’m going with the coil packs and plugs as the cause. Had a similar problem with a V6 Hyundai at about the same time.
The good news is that the coil packs are relatively inexpensive and easy to change,
So Sea Foam or Marvel Mystery Oil is good for my situation, but Lucas Upper Cylinder Lubricant is not a good choice?
I’m a little over 100k miles. I can definitely do the coil pack switch. I agree that it’s an easy thing to do.
I don’t think it’s burning oil. I’d love to get the engine changed under the lawsuit, but I don’t think it applies.
That seems like a great idea. I wonder how much it costs.
Did the mechanic clean the intake valves? How much did you pay?
Carbon build-up on the intake valves can cause cylinder misfires under certain conditions, usually just for a few seconds.
Along with the fault data in the computer, there is also “Freeze Frame” data that shows the engine operating conditions when the misfire occurred. That data is erased when the customer erases the diagnostic faults.
Faulty ignition coils can also cause misfires.
Tester
I don’t know if he cleaned the intake valves. I paid $700 for the carbon cleaning.
For that amount of money, I hope a complete carbon cleaning job was performed; a thorough induction cleaning. The engine should not need another induction cleaning for 30,000 miles.
Any information on your invoice?
That’s the thing. On a web forum we are all just guessing. Unfortunately, many “professional” shops are also guessing, just going down the list from easy to hard or cheap to expensive until they stumble on to the problem. The simple fact is, a test drive while monitoring the appropriate live data with a scan tool while duplicating the complaint will lead you right to the cause. Of course that costs money too.
Hence the reason they often get changed first, whether they’re needed or not.
Which as you know is common on these engines.
Really depends on where you are and who’s doing the work. $150 to $350 sounds reasonable.
How about a weak or broken valve spring?