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Discussion Starter · #1 · (Edited)
Per my introduction about just getting this '20 VT and starting maintenance...I'm having my CEL coming on frequently.

I bought my car about 6 weeks ago with 32K miles on it. About a week after I got it, it had the CEL with misfires on random, 2 and 4. However the car seems to be running great.
It did that 2 times (both random, 2 and 4 ) after my first week, and I noticed that when it triggers, it happens right after I start the car , let it warm up until rpms go down and drove out of my driveway (screen pops up with maintenance issue, and scanner shows misfire only right after I drive off). The fist time this happened, I drove it for about 10 days with the CEL on, and history on scanner showed no other misfires. So, I've cleared 2 CEL's in the first 3 weeks I had it.

Last week, I went 1 whole week without CEL (driving every day), so I decided NOT to change my plugs (already purchased and ready to swap out). Per dealer, plugs are not warranty items, but coils are. So the plan was to change my plugs, and if it popped up again, take it to the dealer for warranty work.

Then, after not driving car for 2 days over the weekend, I got CEL again this morning right after pulling out. I let car warm up for a minute, it went down to it's regular 750 rpms, but I did not sit an extra minute...now thinking I should give it 2 mins. Then, on my 30 mile drive to work I got a record 39mpg WITH THE AC ON! So, car is running great, but this CEL is a thorn on my display.

I'm going to scan it now that I'm at work and reset it, but any ideas? Is this normal? Should I just let it warm up another minute, or should I change the plugs?

Thanks

Edit: Ok, after a minute of thought, I realize I was spoiled by my last car that I never let warm up , and probably should give the oil some time to circulate...prob gonna just let it warm up more. But still wondering what other people are doing. Other threads suggesting you do not let car warm up are confusing.
 

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Swap your coils around and see if the misfire changes cylinders. That will tell you for sure if it's plugs or coils.
 
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Usually one will fail at a time, but it's worth swapping 1-2 and 3-4 just for troubleshooting purposes. As far as warm up on a VT, it's pretty common that you'll get rough cold starts, but it shouldn't throw a CEL. I just let it to do it's thing until the rpms drop down and settle. at that point it's warm enough for basic driving.
 

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2015 RB Accent-not so stock 🤫
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Thanks, but cylinders 2 and 4 both at the same time, repeatedly? Does that happen alot?
It's a waste spark system where 2 and 4 fire simultaneously and 1 and 3 do the same.
When 2 is making the power stroke then 4 is firing at the same time for emissions and burning off any extra fuel in the exhaust stroke.
Same goes for the 1 and 3 strokes.
That's why it was suggested to switch the 1 and 3 coil to where the 2 and 4 coils are now.
Once that's done if you're now throwing codes on the 1 and 3 you can be certain it's in the coils.
If 2 and 4 are still misfiring after the swap you have other issues.
Hope this helps. 👍
 

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2015 auto VT, 2013 manual VT × 2
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Also you need to know the plugs and gaps in the car, fuel type used, mods on the car, and if it has the oem tune or not? Any one of these can easily cause the issues. I have yet to see any oem coils fail at that mileage just FYI.
 

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Discussion Starter · #7 ·
@trdtoy I have the recommended NGK plugs and will check the gap too, if I change them. I also thought it might be the fuel, as after I bought the car I ran a full tank with no CEL, then I put 93 in it and got the 2 CEL's. Then I went back to 87, and ran for a week with no CEL. But now that it happened again, making me wonder what's going on. No mods or tune on car. Car is running good still, so will probably do what @misnblu suggested here if CEL hits again (swap coils), then maybe change plugs. I'm also giving it an extra 30 seconds to 1 min to warm up in the morning (after the rpm's go down). Good info on 2/4 strokes, that makes sense.
 

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Check plugs and gaps is priority #1. Also be sure the car has the proper oem coils in it. Also check the battery health. Also only top tier 91+ fuel. Have you confirmed that it has the oem tune in it or is than an assumption? You can't make any assumptions when trying to sort issues out as you may dismiss the actual issue and waste a lot of time and $ in the process.
 

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Discussion Starter · #9 ·
@trdtoy Ok.I am the 2nd owner, and the car is just over a year old. The carfax shows the car was only taken to the dealer for regular oil changes with no other issues cited. It is an assumption that it has not been tuned. How can I check that?

When I got out of work yesterday, I was letting the car warm up an extra 30 seconds to 1 min, and the CEL triggered again , while I was sitting. So I am guessing it just takes a min for the CEL to trigger after the car starts up (not a warm up issue). When I got home I scanned fault logs and it shows 300 301 302 and 304. Most of the codes have been 300 302 and 304, so I went ahead and swapped coils 1/3 with 2/4. Car is still running good. No CEL on my way to work or driving around last night for 45 mins (to make sure my coil swap was good). I will look forward to the next CEL codes.
 

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Datalog of the car is the easiest way to know if stock or not that anyone can do. Pulling the tune file is another way but not as easy or cost effective for most to do.

See if you can find out the misfires per cylinder for the current and avg over last 10 drive cycles in the ecu. This can be done with some scan tools or with the torque app and a good reader used with it that can also be used for a datalog.
 

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Discussion Starter · #11 ·
@trdtoy I bought the ODBScan LX dongle and have just been clearing the fault codes, so it doesn't show any history. When I bought the car it had a history of about 1000 miles before I bought it of a seatbelt sensor and airbag sensor (I'm guessing that was something triggered while at the dealer). Other than that I don't think it shows me a history. Whenever CEL triggers for misfires, it seems to be once every 400 or 800 miles.

On 2nd day after reset and no CEL. I filled up with 89 (station had 86, 89 and 93)...car running great. So it leaves me to wonder how even the dealer might find the issue if it is an intermittent CEL.

My main concern is passing inspection next year. I think there is something in the 'puter that prevents inspection after CEL reset, right? So if this thing is triggering every week or 2, that may be an issue. May end up having to leave it at dealer for a 3 or 4 weeks for them to figure it out (which will suuuuuk).
 

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You have to go to test results and let it do a full refresh to see the misfire history per cylinder at the bottom of the list that populated.

Yes if you do not have the drive cycles on the ecu it will not pass inspection. Although new cars are exempt for several years in many areas for emissions.
 

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Discussion Starter · #13 ·
@trdtoy Ok, thanks for all the detailed information. I will look for detailed cylinder history. I looked before I reset it last time but did not see it, I will look again next time.

And, I did not have to wait long...I think it is more like every 200-400 miles it is actually tripping CEL. Yesterday , again about 2 mins after it started it showed random, 2 and 4. So, this weekend I will change spark plugs. If it triggers again after that....it will probably sit at dealer for warranty service for a few weeks/months. Last time I was there they were on 2 month appointments for service calls.
 

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Just check the test results section and refresh before you clear any codes as that will also clear the misfires per cylinder as well.

Also if you have torque pro and the android device with that reader you can easily get a short datalog to see if the oem tune or not. Just need to set it up properly before doing so.
 

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I can't recall on torque lite. I advise all get torque pro for the one time $5 payment.
 

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Discussion Starter · #17 ·
@trdtoy Update: I bought the full version of torque, yeah it looks a little nicer. I changed my plugs over the weekend, drove it for about an hour, no problems. In fact it (maybe it was just me since I changed the plugs), it purred noticeably smooth. Then the next day as soon as it warmed up and the revs went down, I waited about 20 seconds, moved it out of the garage and the CEL triggered again. Again with 300 (random) 302 (cyl 2 ) and 304 (cyl 4). Trying to reach dealer today.

Wondering if there is anyway I can get it to pass inspection next year without having the dealer work on it, but it should still be under warranty so going to prob let them take a stab at it.
 

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Discussion Starter · #18 ·
Well....took it the dealer yesterday to have them diagnose it. Also yesterday it was still running great, got 39 MPG on my 40 min commute. It's such a great car. Just wish this CEL thing would go away.
They said it will take 1 to 2 week just to have someone diagnose it.
 
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