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Crosspost - 2019 Veloster N misfire/fuel issue


Well-Known Member
I also wouldn’t breathe too much into the BOV venting. Hyundai’s boost control systems are weird and the BOV goes off on my car at all sorts of random times. It’ll even double vent sometimes. I know people had problems with the BOVs on the VTs and the only one that would activate as fast as the factory sensors needed was the Synapse models. I’m pretty sure Cyngus is a big fan of them for this reason.
Yeah I've pretty much ruled out the JB4 being any part of the issue. It happens with or without the JB4 so I've crossed that out as the culprit. Both sets of plugs are gaped the same, .024in.

I've actually never run the car on any other mode than custom/N so I'm not sure, I'll give it a go tomorrow. I'm going to leave the OEM plugs in for now. The car performs drastically better with the OEM ones, throttle response it's night and day better with the OEMs. I ran the OEM ones gapped down for 2k miles with my JB4 and they were fine.

It's the Turboxs hybrid BOV. Yeah it does vent when I let off the throttle but in this case it's venting when I'm not letting off the throttle. The throttle feels like it's doing something independently from the pedal. I thought the power was dipping but the log shows it spiking up then back down. It's just odd.

Cygnus X-1

Well-Known Member
You can try HKS M45XL plugs, which have projected tips like stock. I found the stock plugs (re-gapped) to be pretty bad with the JB4 with even just mode2. Just goes to show... Every car is different.

As far as the grounding points not helping, don’t know what to tell ya. Helper wires would be the next step. As you noted, heat and humidity are performance killers.

R Veloster N

Well-Known Member
@Jigbits Thanks for the info. I'm glad you're not utilizing an HK BOV.:) That's just another possible problem eliminated.

Well, at least we're working in the right direction.
Helper wires would be the next step. As you noted, heat and humidity are performance killers.
Absolutely agree!
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So I've been poking around pretty much every day trying to figure this problem out and I figured it out.

It's the JB4.

Not the software apparently but the hardware I guess. I was talking with someone else that just installed their JB4 and they noticed a slight jerk but from the sound of it nothing like mine. Mine felt like full on whiplash inducing bucking, like alarmingly so sometimes. I had already flipped some of the bits on and off and tried different mapping including map0. It was still very prominent in map0 so I assumed the JB4 probably wasn't the issue.

After talking to the other person I decided to just pull the whole JB4 out of the car. The bucking stopped completely. I even put the NGK R plugs back in and still the bucking was completely gone. I put the JB4 back in after a round trip to and from work. There is some small jerking when the turbo is kicking in but the bucking in that odd 2nd/3rd gear 3-4k rpm range is gone. One of the plugs must have had a bad connection but they were both snapped firmly into place.

I did one other thing to the JB4 before I unplugged the system which maybe also could have helped, I dunno. My intake is coming in today so the other day I anticipated removing the air box, which is where my JB4 sits, and relocated it to the top of the fuse box. I noticed when I went to move it the case was burning hot, my car had been off for well over an hour with the hood open to cool it down, I couldn't even hold it. Not sure what the operating temperature is for the JB4 but it was incredibly hot. The new location on the fuse box is much cooler. I can handle it right after turning the car off no problem.

So yeah mystery solved I guess. I take back what I said about the NGK R's they seem to be perfectly fine knowing what I know now.

R Veloster N

Well-Known Member
Good to know and I'm glad you were able to diagnosis the possible problem. I know electronics don't like excessive heat, without a heatsink of other cooling method.

It's tough for anyone here to know, it's just best guess.
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