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Discussion Starter · #1 ·
Hello everyone. I'm new here. I live in south Texas. I've recently purchased a 2015 kia Forte5 sx for my wife. It has less than 40000 miles. I've had it a month and it's already giving me problems. Misfires and boost issues. Anyway, I know this isn't the right forum for repair advice so could someone point me to the best forum to ask my questions? Thanks!
 

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2015 and under 60k miles - could it be still under warranty?

When you say - boost issues - what do you mean?

Things to check.
First if the previous owner had any modifications on the car.
Then, those symptoms point to: spark plugs (replace them, 40k miles they are ready to go despite what manual says - those have tendency to die prematurely due to very harsh conditions), then fuel - pour higher octane rate petrol, check air filter, and look on the all the pipes after filter all the way to the manifold.

There could be more issues down the line, but those are the easiest to check.
 

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I agree with everything PLP said.

Can you give a little more detail about your issues?

Without more details I would say two good first steps would be replace the spark plugs with either the oem NGK's or with some HKS plugs. Make sure they are gapped appropriately (between 0.028-0.030"). If you are not tuned stick with the stock heat range 7 plugs or maybe go up to heat range 8.

Using premium fuel would also be an easy option. Other than that. Change the oil with some quality sn plus rated oil. Penzoil ultimate platnum or amazon basics would be fine. Use only an genuine kia/hyundai oil filter.

Do you have an check engine lights illuminated? If so either go to autozone and have them scanned for free or scan them yourself.
 

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Discussion Starter · #4 ·
Oh I have plenty of details. Lol. Just wasnt sure if I should start spilling them out in the introductions forum. But anyway here goes. It all started with "the wave" . Holding the gas pedal in one spot while moderately accelerating would sometimes produce this surging sensation. Which apparently is common on these cars(at least I read it was on the velostars). But anyway once I noticed that I started paying close attention. Then one day while I was accelerating it kinda skipped a beat and threw a cel. Got home and hooked up Torque pro to find that it was a cylinder 2 misfire. So first thing I did was was replace the plugs. All orielly had was champion 9409. so not knowing any better I got those. I believe they are heat range 8.old plugs looked fine and had a nice consistent tan color on them. While I was changing the plugs I swapped the #2 coil with the #1 coil. Test drove it. It threw a code again but this time it was misfire on the #1 cylinder. So I figured hell yea it's the coil. Bought a new coil and installed it. Test drove and again threw a code. Checked it, and now it's a random multiple cylinder misfire😕. So I got to thinking and when I put the plugs in I assumed they were pre gapped + I didn't have a gapper. So I went bought a feeler guage and the next day pulled the plugs. Sure enough the gaps were huge! So I gapped them down to.028. One thing I noticed was the spark plugs color was already white and crusty and flaky. All 4 of them. A far cry from the nice tan color that was on the originals. Anyway I put them back in after gapping them and it didn't help. Matter of a fact it seems the problem kept getting progressively worse by the day. But this time I'm driving around with Torque hooked up because I noticed the car had no power. That's when I realized the boost wasn't going any higher than 3-4 psi. But I also noticed that when I would stop at the store or something and then get back in the car the boost would work again(15psi) for the first 2 or 3 minutes and then go back to being limited. I'm new to using Torque so I'm not sure how to do data logging and stuff or even what the numbers mean for the different pids. In the beginning the misfires would only happen under moderate acceleration. But now it's happening all over including a somewhat rough idle. The car is bone stock and according to the Torque app these were the first cel's and the codes had never been cleard. I've only had the car a month. Im about to pull the plugs again to see what their color is and I'm going to put the ngk's back in and see what happens. While I'm at it I'll check for air leaks at all the piping.
 

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Discussion Starter · #5 ·
I'm starting to think these spark plugs may be my problem. They have been in for 2 days and the ceramic already came loose on one of them.
 

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Discussion Starter · #6 ·
Okay I got the old plugs back in and it seems to be miraculously driving perfect. LOL. So I'm thinking my original problem was the bad coil and I swapped it out around the same time as putting those crappy plugs in. But then the plug started causing all kinds of issues. I'm going to see about finding a new set of nkg's. I'll be taking a trip to San Antonio tomorrow and I will come back and let y'all know how it did. Should I clear out the codes or let them clear out themselves?
 

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Okay I got the old plugs back in and it seems to be miraculously driving perfect. LOL. So I'm thinking my original problem was the bad coil and I swapped it out around the same time as putting those crappy plugs in. But then the plug started causing all kinds of issues. I'm going to see about finding a new set of nkg's. I'll be taking a trip to San Antonio tomorrow and I will come back and let y'all know how it did. Should I clear out the codes or let them clear out themselves?
You did what I was about to suggest. If the old NGK's looked ok then checking the gap and putting them back in would be a good move. Now, depending on the state of the other plugs, it's possible that excess stress could have been put on your coils. So just keep an eye out for that. Hopefully you just fixed the issue with the old plugs but if it persists then hopefully you can diagnose it by swapping around could like you did.

Congrats on hopefully fixing it though! Clear them or leave them. It's up to you. If you leave them then they will probably clear themselves before long if the issue is gone. But if you clear them and they come back then you will know sooner if the issue remains.
 

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Discussion Starter · #8 ·
Thanks everyone! I think it's fixed. Cleared the codes as I left for San Antonio. About a 5 hour round trip. Not a single hiccup or cel. One thing that did happen though is for some reason the traction control light came on and stayed on until I stopped somewhere. Once I started the car back up it was gone. 🤷‍♂️
 

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Discussion Starter · #10 ·
On this car, the traction control off light (from pressing the button) is a Different Light than when it's activated. It hasn't happened again since Saturday so hopefully it was a fluke
 

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Discussion Starter · #11 ·
OK so the car has been running great. Seems to have all its power. No check engine lights. No pending cel's. It's idling smoothly. Seemingly no problems. Before the previously mentioned issues arose I was regularly getting 28-29 mpg according to the display on the dash. While I was having the problems the mpg dropped down to 22 mpg. Well since I fixed the problems the mpg has only went back up to 24.5 and has been on a steady decline since. It's right at 23.9 now. I have it set up so the mpg does not reset with every fill-up. Air pressure is good in the tires. One thing I haven't done was replace the original spark plugs yet. Lephoenix mentioned something about extra stress being put on the coils during the previous ordeal. Could this have something to do with my decreased mileage?
 

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Are your driving habits any different? What about the weather? When it is really hot I think I have seen my mpg go down. I just checked the weather in San Antonio and it looks fairly warm.
 

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Discussion Starter · #13 ·
It has been pretty hot here. I'm even farther south than San Antonio. Triple digits at this time of year are commonplace. One thing i know for sure that is affecting it some is idling. Picking up my daughter from workouts and softball I sometimes sit with the car running because I got there early or she gets out late. I don't think it should affect it that much though. Also my wife has been working from home lately so the car has been getting more city driving than highway driving. And I realize both of these situations will affect my mpg. It just seems a little excessive.
 

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There could be an underlying issue. If you had a coil problem I would expect you to be still having misfires.

And it does seem excessive. But I have noticed similar swings in my mileage over my last 5 years of ownership. It can be frustrating and even brand new we don't get good mileage unless you really are trying. Even then its not really "good" by today's standards. Losing 4-5 mpg with excessive ambient temps, longer than normal idling, and increased city driving isn't too surprising to me though.
 
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