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Diagnosing Possible Misfires – Veloster turbo
It seems that a common issue with the Veloster turbo are misfires. These misfires can be caused by a large number of reason but here I will try to address the most common problems, how to diagnose them, and how to fix them. Chances are if your VT is having a misfire issue you will notice it. You hit the gas pedal waiting for that turbo rush and all the sudden the car hiccups, stutters, and jerks. This is a saddening event. Disclaimer: I am not a mechanic, I do have many years of DIY experience with cars but am far from a professional. If you blow up your engine by misdiagnosing and incorrectly installing a part, that will lie with you.
I will do my best to update this post with new information, techniques, and maybe links to DIYs for some items as they become available. If you see anything in this that is either incorrect or misleading please PM me and I will make sure to correct it.

Symptoms
As stated above, if you feel sudden stuttering from the engine your car is more than likely misfiring. It is usually an obvious jerking (not to be confused with “the wave” that is commonly seen during partial throttle and is more attributed to the stock intake design and stock tune). You will also see your Check Engine Light blinking as the misfire is occurring.
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Possible Problems
The misfire can be caused by a number of different reasons, so let’s go through the list of common issues that have caused misfires and determine what exactly is happening in your case.

1) Fuel delivery. This is a design flaw with the low-pressure part of our fuel line that attaches to the high-pressure fuel pump under the hood. There has been a recall issued by Hyundai for certain VT’s, full details on this and a way to see if your car is affected by the recall may be found in this thread; VT Fuel Line Service Bulletin.

a. Diagnosing. To find out if this is your issue you will need two things. An OBDII reader and some kind of logging software. The preferred reader is the OBDLink MX/LX, preferred software is Torque Pro for iPhone or Android, and either OBD Auto Doctor or Dash for Windows. Once you have these set up you will need to monitor your fuel pressure. If your fuel pressure is steady at 2200 psi then you are probably OK here. If it begins dipping below 2000 psi and steadily declines even though RPMs are going up then you will want to replace your fuel line.
b. The Fix. To fix the fuel pressure problem you will need to replace your fuel line. Even if your car is not listed by Hyundai as a recalled vehicle, you still may need to fix it. There are various vendors that have created a replacement fuel lines that is leaps and bounds better than what is offered by Hyundai. A DIY tutorial may be found here; VT Fuel Line Replacement - Google Docs
A List of available aftermarket fuel line kits may be found here; Scroll down to “Fuel Delivery”

2) Spark Plugs. Another common issue is a faulty spark plug. Usually a ceramic insulator has broken, moved, or been damaged in some way. An incorrect gap or broken electrode are also common issues that can arise. Finding a completely fouled spark plug is much less common but like the other issues is easy to diagnose and fix.

a. Diagnosing. To find if this is your issue you will need to pull out your spark plugs. You will want to try and make sure you know which cylinder each plug came from. Make a visual inspection of each plug by making sure the ceramic insulators are in good condition, checking the gap of each plug is at 0.028” and that all electrodes are intact, and seeing if all four plugs appear to have a similar “wear” or “patina” to them. If one or more plugs is completely black and covered in gas or oil you may have a fouled out plug. Take pictures and post them if you need confirmation on the possibility of a bad spark plug.
b. The Fix. If one or more of your plugs appears to have broken then that is probably your culprit, it would be best to replace all of your spark plugs at this time. Buy new plugs, gap them to 0.028” and place them in the car. Hopefully your car has returned to normal.
Disclaimer: If this is your Youtube video, please PM me so I may give credit to you.

3) Spark Plug Coils. The coils that Hyundai has used for our cars seem to have a short lifespan. It is not uncommon to find that one or more of your coils has gone out after 50,000 miles or so. To find out for sure can be a multi-part process.

a. Diagnosing. You will again need an OBDII reader and appropriate app. If a coil is the issue you should either seeing a flashing Check Engine Light (while the misfire is occurring) or your CEL light is on. You will want to connect your OBDII reader and find out what code is being shown. A P030X in which “X” is the cylinder in which the misfire is occurring. (Cylinder 1 is located on the left side of the engine when looking at it from the front of the car, or the closest one to the oil filler cap.) The best thing to do is move the suspected coil to a new cylinder, clear the codes, and try to replicate the misfire. If you again get the misfire, pull the code. If you do indeed have a bad coil, the CEL code should change to match the new cylinder you moved the coil to.

b. The Fix. To fix the issue simply replace the bad coil. Replacing just the faulty coil should be just fine, no need to replace them all unless you feel the need. Although if you have multiple coils that are faulty then replacing all of them at one time may be the best course of action. To source OEM coils either search one of the Hyundai OEM parts distributors or SoCal Garage Works, a supporting vendor.​

4) Dirty Valves. As our cars get older and thanks to the nature of GDi engines your valves will get dirty. There are things you can do to slow down the effects of this like a good oil catch can set-up, using high grade fuels, a quality air filter, and going by the factory recommended schedule of using Techron to clean things out.
As the valves begin to get dirty they may no longer seat correctly, thus hampering air intake and exhaust flow and can create misfires. Diagnosing this issue is a little trickier as nothing may appear “wrong” but upon very close inspection by a trained eye things aren’t lining up. (Please note: this is a much more involved process, if you feel at all uncomfortable, it is recommended to have an experienced mechanic perform this diagnosis and repair.)
a. Diagnosing. To begin you will need a borescope (similar to this). Pull out the ignition coils and spark plugs and guide the scope into the cylinder. (Alternatively you can try to remove the cold pipe and go through the throttle body, or remove the intake manifold.) You will no doubt see that there is carbon build-up. The main thing is seeing if the valves are seating correctly. If you see gaps between the valve and head then there is major build-up and will need to be cleaned.
b. This Fix. Professional media blasting has been the most common over the years. This involves removing the head and blasting the valves with a “media” (usually walnut shells) to clean off the built up carbon deposits. This is a job for a professional mechanic.
As this common GDI problem becomes more mainstream and more cars out there are using direct injection there are now more options arriving on the market. Chemical products that do not require removal of main engine components have begun to emerge and become more popular but with mixed results. Although they may be somewhat effective these chemicals have not yet reached the level of walnut blasting. They could however slow carbon buildup when used on a regular basis such as during oil changes or every other oil change.​

Conclusion
I hope this has been helpful, and as always if you have questions ask them. I am by no means and expert but I and many others on this board will do our best to help you with finding the source of your issues and getting them resolved. Not all misfires are caused by the above issues but the vast majority are. If your car is stock, or lightly modded and it still falls under warranty, then you may want to the dealership first. Some of these things can be costly and incorrectly diagnosing and “fixing” the issue can cause more problems. If you do not feel comfortable with this type of work then please consult a professional mechanic.
 

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Discussion Starter · #2 ·
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sticky request
 

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Torque app along with a good obd2 reader and hyundai advanced pids is a good tool to help diagnose things as well. Will show you detonation events well before they get to the point of light flashing on the dash or cel lighting up.
 

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Yesterday I got a CEL for Cam Timing Position Sensor: Over-Advanced Timing.

Happened at about 35mph steady speed in average traffic. No physical felt change, just the CEL came up.

I reset the CEL since it drove fine almost 70 more miles.

No idea what really happened, was told "timing belt stretched most likely" by an older mechanic here at work.
Been having issue after issue once I hit 70k on the odo.
 

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I finally got hit with this misfire. Part #s seem to be different from the 2013 to the 2016 model, anyone know if the the coil packs from 2016 would work on a 2013? Can't seem to find any concrete information on this other than 3rd party manufacturers listing the same part # for 2013-2016.
 

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so im having some trouble here... I was getting misfires and flashing CEL and no power on acceleration, so I replaced all my plugs... didnt help, I replaced all my ignition coils... helped for like a week but now My VT idles really rough, to where it drops below 500rpm and then back up. And on hard acceleration I loose power, CEL flashes and sometimes I get misfire errors, but its random, sometimes its cylinder 3, sometimes its 4 other times its 1 and 4, and so on. And I checked my VT on that website and its not one that is recalled for the fuel line. Also in the morning when its cold the car feels and sounds like its gonna stall on my when warming up. Im at a loss
 

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so im having some trouble here... I was getting misfires and flashing CEL and no power on acceleration, so I replaced all my plugs... didnt help, I replaced all my ignition coils... helped for like a week but now My VT idles really rough, to where it drops below 500rpm and then back up. And on hard acceleration I loose power, CEL flashes and sometimes I get misfire errors, but its random, sometimes its cylinder 3, sometimes its 4 other times its 1 and 4, and so on. And I checked my VT on that website and its not one that is recalled for the fuel line. Also in the morning when its cold the car feels and sounds like its gonna stall on my when warming up. Im at a loss
You'd really need to data log it and gets codes and review mods and maintenance history at a minimum to begin problem solving.
 

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I replaced all my ignition coils... helped for like a week but now My VT idles really rough, to where it drops below 500rpm and then back up. And on hard acceleration I loose power, CEL flashes and sometimes I get misfire errors, but its random, sometimes its cylinder 3, sometimes its 4 other times its 1 and 4, and so on.
I know it's a little tedious, but I'd suggest going back and inspecting your plugs again. If any of ones might had a defect or was mishandled, it might have developed a crack or some other flaw that didn't appear in the first week.
 

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I bought a 14 turbo last month. I was getting cylinder 1 and 2 misfire and random misfire. I put new plugs in from the dealer but it didn’t help. I swapped the coils from 1 and 2 with 3 and 4. Was good for 3000km then did it again same cylinders 1, 2 and random. It’ll get a rough idle sometimes but not always. Sometimes I can turn off the lights and the rough idle will go away and sometimes not.
 

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Using premium fuel? Proper oil, filter, and OCI? Fuel line replaced? Mods on the car now?
 

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I use regular gas (87) I did try using premium (91) for a tank but no change. Mobil 1 synthetic oil and filter (5w30) just changed 2000km ago when I did the rear main seal. Fuel line I assume is original. I have the fusion app and fuel pressure is around 2150psi wot and doesn’t drop. As far as I know only an injen cai with k&n filter. I put a forge bov on it a week ago because the factory one had a tear in the rubber. I’ve only had the car a month.
 

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you stated the coils were changed, but what about the spark plugs? @14velosterturbo
 

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Premium gas only. Mobil 1 is a no no. 4 qt oil changes of 5w-40 or 0w-40 in a better oil. OEM filter. 3k mile OCI. Fuel line could still be the issue. You'd have to log and know what to look for to spot it. Not knowing the mods may also be an issue. It could have a tune and you're running 87 in it. What plugs and coils exactly are in it(part #'s)? Plug gaps?
 

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I tried a tank of premium fuel and it didn’t change the issue. I also ran it almost out of fuel and put some 94 in it but no better. I used 5w30 cause that’s what it says to use. What would be best for a Canadian winter. What’s a better oil that’s not overly expensive as I’ll be changing it often. Coils look factory. Plugs were autolites when I bought the car and the gap was way out. It was doing this when I bought the car so I got plugs from the dealer and gapped to .028. What should I be looking for in the fusion app. What should fuel pressure be at idle?
 

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Not sure if the intermittent rough idle has something to do with the misfire. It’s about 50% of the time it’s rough and it’s completely random. Didn’t throw the misfire codes for 3000km. Sometimes when I get home from work and it has a rough idle I can turn off the lights and it’ll smooth out.
 

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Ok so you're in Canada so I believe 94 is the highest pump gas which is what should be used at all times.

5w-30 is ok but no longer what H recommends. Pennzoil platinum or ultra platinum should be available in your area. Use OEM filters. Change every 3k miles max.

Look on the coils and the plugs and there will be a part number. List them if you will.

Look into improving the ground points on the car in and around the engine bay. There is a thread on it in here if you search. That can cause some of these issues as well.

Idle fuel rail pressure should be 40 bar and WOT should be 150 bar. The WOT pressure not holding can be a culprit of misfires. You'd have to datalog to pick up on this as an issue. And do so with an obdlink logger or better to have the best chance catching it.

Another thing to look at is the evap solenoid above the throttle body. It can leak at times and cause issues before a CEL will pop up.

Also always good to check for any boost/vacuum leaks especially on a used car.
 
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