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Discussion Starter · #1 ·
Twice in the past two weeks, my VT has died when I start to press the throttle in while rolling. Both times the vehicle has been rolling along at idle when I started to press the throttle in when the engine dies with no warning, returning to the "On" position (As if I'd pressed the Start button twice without holding in the brake).The first was on the highway in the middle of SoCal traffic, and with the remainder of my speed I was able to move four lanes over onto the shoulder. Turned the car off, back to the "On" position (without starting the motor), checked for codes (none), and restarted the car with no issues.

The second time was just today when I attempted to pull up a small hill into the post office. Same situation, rolling at idle, dies when I hit the gas (even gently). This time, attempted to immediately restart the engine. Would turn over very strongly, but not start. Checked for codes (none), checked the engine bay for loose grounds (none), got back in, and attempted to start, and it started just fine.

The lack of codes or any other issues running leads me to believe it may be an electrical issue, but I'm not sure what? After the first time it happened, I redid all of the grounding locations according to the other post by trdtoy, which hasn't solved the issue. If it was a fuel issue I'd imagine it would've thrown a code but clearly hasn't. Fuel line has already been replaced anyway and fuel pressure reads good every time I've checked it on my code reader (which admittedly isn't that often, but still). Oil changed with Penzoil Uplat 0w-40 and OEM filter within the last 1000 miles (and still full). Checked spark plugs yesterday for fouling and gap (no fouling, only minor gap adjustment). I can't think of anything I've done recently mod-wise that would start to cause an issue like this to crop up so suddenly, but full list is as follows:

Electrical:
1600w amp + subs (several thousand miles, no issues)
All four door speakers replaced (above, no issues)
Ignition fuse killswitch (Not particularly recent, but can't imagine how this would cause it anyway)
LED cabin light replacements (Probably not)
H9 Headlight conversion (several thousand miles again)
Boost gauge (backlit)

Engine/Everything else:
Dual OCC
DIY cold pipe with BOV (OEM BOV port blocked off)
Resonator delete
3" to 3.5" intake
MBRP 2.5" catback

Any ideas as to what might be causing this? The only thing I can think of would be to monitor fuel pressure on the OBD2 scanner to make sure the pumps and rail are still good, but other than that I'm at a loss.

EDIT: I should add that this issue is not at all consistent. Like I said, it's only happened twice within the past two weeks and I've been in the driving situation I described (idling at relatively low speed when I start to press in the throttle) more times than I can imagine. Every other time it responds fine.
 

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2015 auto VT, 2013 manual VT × 2
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Check the fuel pressure on a cold engine car off then at idle then on throttle and WOT. Can be a fuel issue and not throw a code and be random. Can also be a crank position sensor without a code and have the same symptoms.
 

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Discussion Starter · #3 ·
What do you mean by check fuel pressure with car off? Car completely off or car set to "On" with engine off? What should it read here?

And for reference, I'm looking for ~500 at idle and ~2500 at WOT, correct?
 

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2015 auto VT, 2013 manual VT × 2
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5 bar acc on car off cold engine.
40 bar idle.
150 bar WOT.
 

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Sounds like your crank position sensor is going bad.
 

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Discussion Starter · #6 · (Edited)
I don't get a reading off the OBD2 at the ACC position

4.8 bar (70psi) at ON
120 bar (1750psi) cold start
38 bar (550psi) idle
62-82 bar (900-1200psi) 2000rpm load
151 bar (2200psi) WOT

Based off what you said it looks fine to me. Idle might be just a TOUCH low which I suppose could cause the stall I described, but like you both say, I would imagine it's rather the CKP. However, with it working fine most of the time, is there a way to test it without firing the parts cannon at it? I would prefer not to have to wait until it's throwing a code/undrivable.

EDIT: Looking through some diagrams I think I'll be able to get to it okay, but if anyone's done it before, was it easier to go through the top of the engine bay or from underneath? Does anyone have the target resistance reading across the sensor? I don't think I'll be able to get a voltage reading off it running considering everything that looks like will have to be removed.

EDIT 2: hvmanual.com says 774 to 946 ohms. Will check this next opportunity I get.
 

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Check sensor per FSM or dealer can check it. If you can swap it if indeed bad do that to proper spec and get the sensor from Albert Hwang on FB.
 

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Discussion Starter · #8 ·
Reading 906 ohms across the sensor. Seems to check out considering it works most of the time but I wouldn't be surprised to learn it's just now starting to fail. I'll probably replace it here soon regardless and we'll see if that fixes it. Luckily it looks like a pretty simple install, especially compared to the CKP that killed my last Kia. I'll update this thread if anything else happens or once it's fixed. Many thanks for all y'all's help :)
 

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Discussion Starter · #9 ·
Sensor replaced (much easier than when they're located under a timing cover, thank god), and car starts. Time will tell if the issue is fixed.. Visually, old sensor appears just fine, if a little dirty (which is to be expected). The car has also been "hiccupping" on the highway, as if misfiring, which I'd imagine was also due to the sensor. Aside from wiping out the hole the sensor was inside, are there any other steps I should take to make sure everything's clean? I decided against spraying any kind of cleaning agent inside until I'd checked elsewhere first.
 

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Just install and tq to spec
 

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Discussion Starter · #11 ·
So, good news and bad news.
Bad news: not completely fixed.
Good news: not stalling at stops/slows any more (so far, knock on wood)

Now, there is a reproducible issue where mildly hard acceleration (>3.5k rpm) will allow rpms to climb normally, but after a couple seconds, the vehicle will begin to shudder as if misfiring. If I let off the throttle at this point, the car will recover and begin to respond to throttle again. This morning, while trying to determine if it was a fueling issue, I held the throttle through the shudder (which only lasted about two seconds) until the shudder stopped, at which point the car did not respond to any pressure on the throttle whatsoever. My gauge would show vacuum moving towards ambient air pressure with the throttle pressed, but there was no response from the engine. After shifting into neutral and seeing still no throttle response from the engine, the engine completely cut off, whereas up until this point it was slowly decreasing RPM's with the wheel speed.

At this point, I'm still in neutral going about 50 down the highway. Pressed the start button, engine fired right back up and throttle response was present again. Throughout this entire encounter, fuel pressure off my OBD2 reader was good (including through the shudder and lack of response to throttle, I BELIEVE that it was still dumping fuel in response to the throttle but my eyes weren't glued to the OBD2 the whole time.

Further, once I got back I found a pending CEL: P2414 O2 Sensor Exhaust Sample Error Bank 1 Sensor 1. As much as I'd like to believe that the whole issue is caused by a faulty cat (and thus give me an excuse to gut it), what I think happened is that something is still wrong with my spark timing, and that when the shudder and throttle response happened, the engine continued to dump fuel and air into the cylinders (which didn't spark) and then left through the exhaust, causing an excess of unburnt fuel to trigger that CEL. Thoughts?
 

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If that's the only CEL or pending CEL after that you may have a fuel line issue. Need to datalog with a good logger(high PID update) to help determine this.

Is this on the oem tune or aftermarket tune? I've seen some aftermarket tunes do this but not an oem tune yet so wanted to eliminate that as a possibility.
 

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Discussion Starter · #13 ·
OEM Tune

I've already replaced the fuel line with steel braided PTFE line, but I was planning on pulling the in tank fuel pump to check for debris anyway so I'll blow out the line when I do so. I didn't have any issues with the stock line before I replaced it about a thousand miles ago though.

I'm not sure how "good" my logger is compared to a dedicated model (Zurich ZR8, it's an $80 harbor freight code reader with a live data feature), but I'd be really surprised if it ended up being a fuel line issue. I'll try paying more attention to my logger when I reproduce the issue after cleaning out the fuel line and pump, and if that's inconclusive I'll look and see if I can get a better logger on rent from an autozone.
 

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That's a code reader with live data not a datalogger. You need to be able to datalog to not only have a better chance of catching the issue but safer as well.

OBD link LX, Torque pro app, android device is all you need.
 

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Discussion Starter · #15 ·
Cleaned out the pump, blew out the lines, retightened everything (not a ton of gunk, but enough that I don't think it was a waste of time). Went on a test drive, same issue.

HOWEVER

Now pending P0336 Crankshaft Position Sensor A Circuit Range/Performance in addition to the O2 sensor code and BOV code.

Now, I didn't use an OEM CKPS to replace the one I assumed failed earlier. I'll order an OEM one and try that next, but unfortunately it seems like my next best bet is replacing the wheel for the crank sensor. Unless anyone has any better ideas as to what might be happening here? If not, I'll probably look into what doing it myself looks like versus a shop quote.
 

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Yes, oem sensor and proper spec.

What are the other codes?
 

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Discussion Starter · #17 ·
P2414 and P2261.

Forgot to mention that when I did that test drive and ran into the same issue again, I lost the tach one of the times it was acting up. Engine was still running and responsive to throttle, but no reading on the RPM gauge.
 

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So CPS and possible vacuum pump issue.
 

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Discussion Starter · #19 ·
The BOV CEL is something that's been happening intermittently since I installed an aftermarket BOV on my diy cold pipe, which I understand is a pretty common occurrence. The overwhelming majority of the time it opens fine. I get a slight surge at very low (around 0) boost but I'm fairly certain I just need to adjust it to open a little sooner.

I really don't think it's connected but I can try testing that too when I go check cranking voltage across the CKP sensor
 

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Discussion Starter · #20 ·
The fact that it only causes problems at or above about 3.5k rpm makes me wonder if it has something to do with the way the spark advancement/ignition timing is supposed to change as engine load increases. Does anyone have a reference for what spark advancement should be at a given rpm or load?
 
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