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Crosspost - 2019 Veloster N misfire/fuel issue

Nomad17

Active Member
#21
I guess it depends how severe this bucking is. I notice power delivery is less smooth and consistent on a cold start. If i hold the accelerator at a fixed position the cars acceleration will fluctuate slightly. This only happens a very short time when cold and if I give it more gas it will go but might be what you're experiencing.

I just chalked it up to it being cold and have noticed similar behavior in other vehicles. Maybe running in normal mode for the first 5 minutes would lessen this, just due to a smoother throttle response.

If the bucking is more severe then ignore what i said and consider leaving it overnight at the dealer.
 
#22
That’s a little more severe than what I’m quoting. They act a little sluggish and buck a bit when they’re first warming up. But if you need to get up to speed you can. It just takes a lil longer with a lil more fight than if she was properly warmed up. But it has never caused me to fear for my safety or have to avoid the hammer lane.
Yeah, maybe it’s a different issue. I need to get it looked at. It almost feels like it’s going to give me whiplash sometimes.

Wish I could capture it on camera but it doesn’t occur every time and I obviously don’t want to hold a phone in my hand...
 
#23
I'm definitely getting the same thing. I get what feels like fuel is being cut off.

It never happens after a cold start from sitting over night. But it almost always happens when I leave for lunch or leave after work and the car is not completely cold.

Any ideas what might cause this?
 
#26
Huh I have the same issue. Glad I'm no the only one. The issue got worse after I changed spark plugs, NGK R2556G-9 gapped to .024. I ran my JB4 on map 2, and a similar map 6, with stock plugs gapped to .024 and never really had an issue but right after I changed plugs gear 2 and 3 has this horrible jerkiness between 3-4k RPM.

I've checked the plugs after having the issue since it started after I put them in. I used a torque wrench to put them in and followed NGK's recommended torque originally. I've pulled them out and checked for issues with the plugs themselves. They are fairly black around the threads but the core and electrode are completely clean. I don't know much about this type of thing but from what I've read it's almost like carbon fouling but from what I've read about carbon fouling it shows the electrode and core being completely black, which mine are as clean as the day I installed them.

Which would be odd since I don't think I run a rich AFR on my JB4, I never let it drop below 11.5 and try to keep it around 11.5 at 20psi and lean it out after 5500rpm(tapering down below 15psi) to around 12.5

I've tried to test for when this happens and it's the worst when I don't perfectly sync shifting from 1-2nd or 2-3rd. If I go through gears as quickly as I can without going WOT it jerks really hard. But if I let the RPMs fall to exactly where they should be before letting out the clutch it's almost non-existent. For me at least it doesn't really happen at WOT only when I go between 30-60% pedal (According to my JB4).

I have no idea what the issue really is but the obvious issue is the spark plugs since I never noticed it until I changed them. The stock plugs running 6psi over stock never had any issues but right after I changed them (I've had this conversation with Maggei82 because he has the same issue with the same plugs) everything kind of went to shit.

IMG_20190703_195137.jpg
 

Cygnus X-1

Well-Known Member
#27
Same NGK race plugs here (with same 0.024” gap) and no issues on custom JB4 map 6. I’ve cleaned most of my grounding points (like I keep saying to do), though, along with adding a couple of helper wires.
 
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#28
Same NGK race plugs here (with same 0.024” gap) and no issues on custom JB4 map 6. I’ve cleaned most of my grounding points (like I keep saying to do), though, along with adding a couple of helper wires.

I'd like to give that a try, but don't really know much about doing something like that. Are you talking about cleaning the grounding points on the coil packs or some where else? If it's more than just the coils where are they and how many points are there?

I looked up helper wires and there seems to be a lot of ways to do it. Do I need one of those extensions for the ground on the battery?

Details of what you did would really help.
 

Y0UKN0WITSCHRIS

Well-Known Member
#29
Someone should do a write up of all the grounds on the engine. Or Atleast find a diagram and highlight them to make it easier for the less experienced members to find them so we can try and get to the bottom of this. I personally haven’t worked on my N a whole lot these past few months and this is definitely on my to do list. But on a side note my N has sat for about a week now and it started flawlessly this morning. But the last time I had it out it hard started several times that day and made the tapping noise. The weather was very warm that day 85-90° ambient temp and about 80% humidity.
 

R Veloster N

Well-Known Member
#31
https://www.amazon.com/uxcell-Universal-Ground-Cable-System/dp/B005EEIL3K
https://sharkracing.com/2012-2013-veloster-deluxe-ground-wire-kit/
https://www.amazon.com/uxcell-5-Poi...Red&qid=1563384558&s=electronics&sr=1-1-fkmr2

Old photos but applicable as well. Gives you an idea of what to look for. Refer to the VN engine & electrical schematic for the locations.

WARNING;

*********Make sure you disconnect the battery first!!!!!**********

Use a dremmel tool, ratchet, extension, with 10mm and 12mm sockets. Make sure you do the contact surface and bolt heads as well.

Remember this Cygnus!;):) Don't want to crosspost but it's good information.
20151025_005528.jpg
20151025_005658.jpg 20151025_005707.jpg 20151025_005729.jpg
 

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#34
So I tried fixing up the ground points today. It didn't help. I could only find 3 points though; one on the passenger side near the strut, one right off and behind the battery, and one under the air box. I took the bolts out and sanded down the contact area to bare metal and polished it. I polished up the ground connectors as well and put some conductive grease on them.

I will say now that I've paid more attention to it. It's the worst when it's hot and humid. A light rain with high temps, I'm in Florida so it's 90f+ and 80%+ humidity at any given time right now, it's pretty bad. I've also noticed for me it's still only happening during moderate acceleration. Accelerating slowly and not building any boost is no issue. Going WOT is also no problem. But giving it 50% and 2nd and 3rd is a jerky mess until I get past 4k.
 

R Veloster N

Well-Known Member
#35
Next up is; "spark plugs and coil packs.";) It's a process of elimination. first.

Check all the "spark plugs," for proper gap, fouling and no ceramic insulator cracks.

Check the "Coil Packs" for cracks on the plastic insulators.

Keep in mind, you may have to purchase and replace all the plugs or coil packs. If you do, talk to your dealer service first. Let them analyze the issue as welland see of it's throwing any codes on the GDS. This way, you may be able to get them to replace each under warranty. In the grand scheme of things, they don't cost that much.

Are you running a tuner yet? If you are, you may need to run a different heat range spark plug or at least regap each plug.
 
#36
Next up is; "spark plugs and coil packs.";) It's a process of elimination. first.

Check all the "spark plugs," for proper gap, fouling and no ceramic insulator cracks.

Check the "Coil Packs" for cracks on the plastic insulators.

Keep in mind, you may have to purchase and replace all the plugs or coil packs. If you do, talk to your dealer service first. Let them analyze the issue as welland see of it's throwing any codes on the GDS. This way, you may be able to get them to replace each under warranty. In the grand scheme of things, they don't cost that much.

Are you running a tuner yet? If you are, you may need to run a different heat range spark plug or at least regap each plug.
I checked them first because I really started to notice it after I replaced the stock plugs with the NGK R2556G racing plugs, heat range of 9, I was recommended for the JB4. They are properly gaped and installed with a torque wrench with NGKs recommended torque. There is a picture a few posts up of one of the plugs I pulled to see if anyone could tell me if it was a problem but Cygnus just said to do the ground points. It's got black around the threads but the core and electrode are as clean as the day I installed them.

I'll check the coil packs but they seemed ok when I was pulling those plugs a week ago.
 

R Veloster N

Well-Known Member
#37
I'm not familiar with the JB4 settings, so that's something you'll have to deal with @Cygnus X-1 straight away. It could be exacerbating the issue but this is only my personal speculation. I don't know what the ECU and JB4 coupled are doing, when it's hot and humid where you live.

I'd have to actually see the insulator ceramic tip inside to determine if it's running lean or rich. The outside of the threads doesn't actually indicate anything except, some possible carbon fouling and a possible rich condition. Otherwise, to much fuel. Some of which is typical of all GDI engines.

However, below are typically what you'd see in either a rich or spot spark plug images. The one on the left denotes carbon fouled the one on the right is what the plug will look like, if burning correctly.

Honestly your plugs from the

spark-plug-fouling-1-320600.jpg installation-fouling.jpg
This v is what I need to see;
maxresdefault.jpg
I presume you're running nothing but premium fuel, correct? I don't care what anyone tells you, don't run anything but premium fuel top tier fuel in this engine. If someone tells you differently, tell them to; "go piss in the wind" so to speak."
You can try to run the HK M-Series Heat Range 9 Plugs, 50003-M45HL. However, I don't believe this will cure the issue altogether. Might help but again this is my best guess as well.

Check each coil pack for the proper ohm value. I don't know what the ohm values are for the 2.0T Theta II engine right off hand. I don't have a shop manual but you can call your Service Department, AutoZone, NAPA or O'Reilly's, they should be able to tell you. I can tell you how to check them, once you have the proper Ohm values. If there's a bad one, it will get replaced.

This issue is; another reason to take it to the Service Department and let them do a diagnostics on the GDS. Typical codes the ECU will throw for such issues are ; Engine code - P0303, P03A5, P039B, P03AF, P03B9 and P0302. Which range from; bad coil pack/s, clogged injector/s, bad injector/s, bad spark plug/s.

Yep you're going to have to pull the JB4 as well. Also replace the spark plugs, with the original OEM units as well!:(

Cheap Possible Fix # 1; Buy 3 large black bottles of Chevron Techron. Use one at each fill up, for the next three fill ups. Go to a top tier station to fill up also and not your local cheaper one.

Special Note;
It's possible it just might be a faulty knock sensor but I'm not ready to go this direction. At least until we've ruled out others first. You don't have any plugs electrodes melted or electrode tip, ceramic insulators, cracked, right?;):)

It's a process for sure but worth it in the long run. The more you learn now, the less you'll have to pursue in the future.

You might also purchase a ODB Link; https://www.amazon.ca/OBDLink-Bluet...DB+Lonk&qid=1564430318&s=gateway&sr=8-1-spell

So, you can check what's going on with the car as well. Invaluable little tool, will reads error codes and more. It will also allow you to diagnose and clear them also.

Long post I realize, sorry. However and unfortunately, there's certain more!. It's simply a process of elimination.:)
 
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#38
Ok so I pulled the NGK R2556G-9 plugs out just now to check them. They look fine just like this picture. Little black around the edges but the core and electrode are clean. I don't think it's an AFR issue. My logs are all pretty normal around 11.5 at WOT through most of the RPM range and the cars ECU deals with the AFR while the JB4 is not active (I think the JB4 is only active above 70% throttle).



Just to try something I put the OEM plugs back in. The jerk is pretty much completely gone with the stock plugs gaped to .024. Like you wouldn't notice it unless you knew exactly what you were looking for and it's just a small single jerk right after a shift once you get back on the accelerator. So it seems the issue is at least 90% the plugs fault. So I guess the NGK R2556G-9 plugs were a massive waste of $120.

The JB4 does code reading. The car has never thrown any codes I've checked multiple times. Almost exclusively use Shell premium fuel. Coil packs seem fine but I'll have to get a multimeter from work to check them.

Yeah I'd have to pull a lot of stuff out if I take it to the dealership so that'll be my last resort.

One last thing now that I have a BOV installed I've noticed when it jerks the BOV vents with every jerk. So does that mean the throttle body is closing even though I have my foot on the accelerator? Not only that but I tried logging it with my JB4 and it shows my throttle jumping which is when the jerk is happening. This graph is 1st, 2nd, 3rd gear at moderate acceleration and in 3rd it jerked twice and you can see the throttle shooting up for a split second even though the pedal remains fairly constant.

https://datazap.me/u/jigbits/log-1564434130?log=0&data=1-4-5-9&solo=5
 

Y0UKN0WITSCHRIS

Well-Known Member
#39
Ok so I pulled the NGK R2556G-9 plugs out just now to check them. They look fine just like this picture. Little black around the edges but the core and electrode are clean. I don't think it's an AFR issue. My logs are all pretty normal around 11.5 at WOT through most of the RPM range and the cars ECU deals with the AFR while the JB4 is not active (I think the JB4 is only active above 70% throttle).



Just to try something I put the OEM plugs back in. The jerk is pretty much completely gone with the stock plugs gaped to .024. Like you wouldn't notice it unless you knew exactly what you were looking for and it's just a small single jerk right after a shift once you get back on the accelerator. So it seems the issue is at least 90% the plugs fault. So I guess the NGK R2556G-9 plugs were a massive waste of $120.

The JB4 does code reading. The car has never thrown any codes I've checked multiple times. Almost exclusively use Shell premium fuel. Coil packs seem fine but I'll have to get a multimeter from work to check them.

Yeah I'd have to pull a lot of stuff out if I take it to the dealership so that'll be my last resort.

One last thing now that I have a BOV installed I've noticed when it jerks the BOV vents with every jerk. So does that mean the throttle body is closing even though I have my foot on the accelerator? Not only that but I tried logging it with my JB4 and it shows my throttle jumping which is when the jerk is happening. This graph is 1st, 2nd, 3rd gear at moderate acceleration and in 3rd it jerked twice and you can see the throttle shooting up for a split second even though the pedal remains fairly constant.

https://datazap.me/u/jigbits/log-1564434130?log=0&data=1-4-5-9&solo=5
Kind of a side step here. But in regards to the NGK products. When I was big into Honda’s a few years back I ran into issues with NGK plug wires 2x and then had a spark plug go bad on me as well. I’ve always had a bad taste in my mouth with their products because of this and cringe when I see the name. But maybe their quality has gotten better over the years or maybe it’s gotten worse.. but your post above about the plugs being pulled and the car running better made me wanna share this info.
 

R Veloster N

Well-Known Member
#40
JB4 Questions you're going to have to talk with Cygnus. I just don't know.

Personally, I don't like the NGK's racing plugs. Never had much luck with them in racing bikes either. Did you gap the OEM plugs, as JB4 recommended?

Does it jerk as you described in every mode with the NGK racing plugs or OEM NGK plugs?

Now I have to ask, what BOV are you running? I hope not an HK BOV? When you let up on the throttle, any BOV is going to attempt to vent a bit.
 

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