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Discussion Starter #1
Hello all, new member, first post!

I just bought a used 2013 VT, 88k miles, 6 speed manual, well taken care of, clean car-fax. No known mods other than a K&N air filter element in stock housing with stock air intake. Driving home, car developed misfires, worse under hard acceleration. At steady speeds car ran fine, got 34 mpg on expressway trip home. After reading some posts, I changed the spark plugs due to mileage. It seemed to help at first, but misfires returned. Plugs removed had a bit of brown discoloration, but not burned, wet, caked with deposits or any damage to ground electrodes or porcelain. Gaps only slightly larger (maybe 0.035" max) than those on replacement plugs (0.028"-0.030", carefully checked with feeler guage, as I know from my 33 years in the auto parts business that re-gapping Iridium plugs can cause more problems than a few thou variance will) After reading some posts on here about possible coil pack and low-pressure side fuel supply line issues, I hooked up my scan tool. The only codes I have are for misfires, including all 4 individual cylinders (P0301-P0304) and P0300 random, no P0087 low fuel pressure, yet scan tool indicates only 560-580 psi fuel line pressure at idle, and it stays flat with a only a little variance up and down as rpm is increased to around 3500 in neutral (not gonna free-rev it higher than that). Not having much experience with Hyundai (if you need GM vehicle info, I'm your man,...) I humbly turn to you all for help and advice, so as to not throw away money on things not necessary. I ran my VIN on Hyundai's site, and it does not show any recalls or campaigns relevant to it. Thanks in advance for any and all help.
 

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Normal fuel pressure at idle but you must log at heavier load to see if fuel line issue. If you replaced plugs with the proper ones or upgraded ones and still have misfires then will be coils or fuel supply related. And I hope you're not running lower than 91-93 fuel.....
 

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Discussion Starter #3
Thanks for the reply. I will run my scanner tomorrow while driving, record fuel pressures under load and post back. So you're saying these cars do not like regular 87 octane even when stock even though the owners manual says it's okay?
 

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Yup...
 

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Discussion Starter #5
Okay, good to know I need to run better octane from here on out. Thank you for that info.

I hooked up my scan tool this morning to watch the readings and record them, but for some reason the recording stopped only a few seconds after I started.

Upon glancing at the readings as I continued to work, the fuel pressure moved around, generally between 560-1500 psi, with no misfiring issues under light load acceleration, keeping revs under 3500. The one time it spiked up a higher is when I rolled on the throttle in 6th gear around 45mph. Under that load, the pressure spiked to around 1950-1960 psi, and the engine stuttered, but it didn't trip a permanent misfire code. Does this still sound like bad coils or possibly a fuel delivery issue?

Again, thanks in advance. If it would help, I can upload a picture of the old plugs I pulled out when I get home tonight, although I saw nothing on them that really showed anything (light brown color and even, non-excessive wear/gap erosion/no cracks in porcelain, etc... Let me know

Rich
 

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Okay, good to know I need to run better octane from here on out. Thank you for that info.

I hooked up my scan tool this morning to watch the readings and record them, but for some reason the recording stopped only a few seconds after I started.

Upon glancing at the readings as I continued to work, the fuel pressure moved around, generally between 560-1500 psi, with no misfiring issues under light load acceleration, keeping revs under 3500. The one time it spiked up a higher is when I rolled on the throttle in 6th gear around 45mph. Under that load, the pressure spiked to around 1950-1960 psi, and the engine stuttered, but it didn't trip a permanent misfire code. Does this still sound like bad coils or possibly a fuel delivery issue?

Again, thanks in advance. If it would help, I can upload a picture of the old plugs I pulled out when I get home tonight, although I saw nothing on them that really showed anything (light brown color and even, non-excessive wear/gap erosion/no cracks in porcelain, etc... Let me know

Rich
Do not ever ever ever roll on the throttle at 45 MPH in 6th gear....
 

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Discussion Starter #7
Hmm, interesting. The "up-shift indicator" starts nagging if I don't shift to 6th at that speed while steady cruising on flat ground. To clarify, all I did was slightly roll on the throttle to induce a load once I reached a steady speed. That is when the hesitation occurred. It was not a typical "lugging the engine"
in too high of a gear feel. No attempt at hard acceleration. Again, I really appreciate any and all responses.

Also, I hate sounding like a noob...

Rich
 

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Hmm, interesting. The "up-shift indicator" starts nagging if I don't shift to 6th at that speed while steady cruising on flat ground. To clarify, all I did was slightly roll on the throttle to induce a load once I reached a steady speed. That is when the hesitation occurred. It was not a typical "lugging the engine"
in too high of a gear feel. No attempt at hard acceleration. Again, I really appreciate any and all responses.

Also, I hate sounding like a noob...

Rich
When i had my VT i dont think i ever put it in six gear.... ignore the light... do the upper clutch switch mod...
 

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Discussion Starter #9
So, what information do I need to provide to try and narrow this down? Do I need to more closely monitor fuel rail pressure readings vs rpm and post them here? If so, I will try to get the record function to work on my scan tool so I can do so more accurately.

I can say that fuel pressure under normal acceleration stayed under 1300 psi. Do I need to get on it a bit and get the tach above 4k and see what happens then?

It only spiked into the 1900's when I lightly rolled on the throttle (not hard enough to physically lug the engine) in high gear and that's when the hesitation occurred.

I've read fuel rail pressures in the >2k psi range under load are not abnormal. Is that information erroneous as well?

Is there an ohm spec for the primary side of the coils that I can test, or is that not an accurate test due to the coil-on-plug design?

Again, any help would be greatly appreciated.

Rich
 

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Discussion Starter #11
You should see ~2150-2175 PSI (~148-150 bar) at WOT.

Ignition coil resistance specs are in the service manual.

Thank you very much, this is the info I was looking for. I will be getting a manual for this car in the future (I see PDF versions available for a reasonable price), but since I just bought it, I don't have one yet.
Rich
 

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Discussion Starter #12
Okay, left work today, all is good at first. Booted it a couple times, fuel pressure good (climbed well past 1800 psi), no misfires, runs great up to 4,500-5,000 rpm through 3rd gear and pulls strong.

After a couple of more miles, I get another opening from a stoplight, boot it again, runs fine through first and second, hit third fuel pressure quits rising at just over 1k psi and flutters a bit, engine bogs, then the CEL flashes, but goes back out when I let off and it stays off.

Car drives rest of way home fine since I didn't get on it again.

It definitely seems the issue is fuel pressure related, so does this sound like the low pressure line issue, or could it be with the high pressure pump at the engine?
 

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Discussion Starter #14
I just bought the car, and have been having mis-fire issues when you get on it. No P0087, just P0300-0304 codes.

Changed spark plugs due to mileage but no improvement. Definitely seems to be fuel related as fuel pressure stops climbing with engine speed after driving a few miles.

No obvious mods other than a K&N drop in air filter in stock airbox.
 

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I would recommend 6th Elements Fuel pump (DW65c Hyundai Low Pressure Fuel Upgrade and steel braided fuel lines (PTFE braided line - 6AN) but I don't know the condition of you gas tank (might be full of gunk).
BTW E9C900A has a lot of good info from over the years, also TooGqForYou, Bigbird, Mr.MattyV, rspec2014, TyBardy, trdtoy, and these are a few people Who and Been a Great Help to me in my journey.
 

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Flashing P030* DTCs are a huge no-no with this engine.

What is the mileage of the car? If you have no record of the maintenance history, the absolute first thing you should do is get all cylinders borescoped, a compression test and leakdown test done.

If the combustion chambers and intake valves are excessively crusty with hydrocarbon deposits, have a walnut blast job done.

Factory ‘13 spark plugs are way too hot. Replace those with HKS M40XL plugs gapped to .028” and if over 45K miles, replace the ignition coils as well with OEM.

Let’s make sure the ignition system is healthy and combustion chambers are relatively clean before replacing fuel system parts.

An aftermarket fuel line is much cheaper than a HPFP. After the health check is done, I’d like to see a Torque Pro (TqP) log of a full throttle 3rd gear pull from 3000 to redline.

Until this gets properly sorted, do not put high load on the engine by applying even moderate throttle in a high gear. Otherwise, you’ll eject a piston or two through your block.

This is exactly the type of stuff I envisioned seeing when we went through all the common problems 4-5 years ago. It is very apparent that the prior owner(s) did not do appropriate maintenance.

Thank you very much, this is the info I was looking for. I will be getting a manual for this car in the future (I see PDF versions available for a reasonable price), but since I just bought it, I don't have one yet.
Rich
No need to buy anything.

https://v.gd/xvtsm
 

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Proper heat range 8 or 9 plugs, aftermarket fuel line, and 91-93 fuel should fix it. New OEM coils may also be needed.

The older cars had much worse components and tunes in them and running lower octane fuel makes it even worse.
 

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Discussion Starter #18
To answer E9C900A,

Car has 88k miles, great shape, clean with well documented carfax. Sat on dealer lot for a while through the winter due to disinterest in the Matte paint and manual trans.

Ran fine at first, then the misfires started after pulling out of a rest area and getting on it to merge with traffic.

Changed plugs when I got it home due to mileage and not knowing if they had ever been replaced. Old plugs came out clean and dry, just normal light brown deposits. No gas, oil, burnt ground electrodes, etc... Ran good at first after plug swap but misfires returned after a while.

After warming up a bit, when on the gas over 3,500 rpm, the fuel rail pressure stops climbing (normally not until 3rd gear) at around 1.1k psi, and then the CEL flashes misfires. When driven lightly, car runs flawless, smooth as butter, got 35+ mpg at 75mph on trip home, never registered another mis-fire all the way home, nor in normal driving now trying to sort it out. Only mis-fires when the fuel pressure drops . Only other thing of note, there are light black sooty deposits on tailpipe outlets.
 

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Replace all 4 ignition coil packs. If you don't have the money at least replace 2. I recently had a similar experience. I had 2 completely go out at 62k. Black soot on the exhaust is normal.
 
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