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Discussion Starter · #1 ·
Hi guys, I handed off my VT to my daughter a couple years ago and this week she called and said the CEL came on and that the car felt sluggish in passing ppl on interstate, she said she was at 85 and pushed it to the floor and it didn't respond. I took it to the dealer yesterday and its got a code P0299 (underboost). Car has 102K on it, some deferred maintenance...had them change the plugs, air filter, oil and diagnostic on the code. They wanted to do another hour of diag on it to take off the bumper to check the intercooler for damage or they thought it might be the Boost Sensor, I told them no as I didnt think they knew wtf they were doing. This was my first and only Turbo car so I'm not well versed in them. They want $120 for Sensor (Part 393002B050) and $432 for intercooler (Part 282722B700) plus labor....
Where can I start to inspect parts/change sensors etc to get this corrected?
Is it ok if she ust drives it around town with no boost and the CEL on while I get this sorted?

I took the car out on the interstate and it seemed to pull pretty hard to me, got it to 95 with no issues, so I'm not sure what to think. I haven't driven it in a couple years so I'm not very seat aware of the performance of it.

Appreciate any input!
Thanks!
Derek
 

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In my (completely anecdotal, take it with a grain of salt) experience, typically the underboost code only pops when there's complete turbo failure. You can pop the bumper off to look for damage to the intercooler and other intake tubing yourself, or run a smoke test to pressurize the entire intake system which will show you the same thing.

You can check voltage and resistance across those sensors yourself. Hyundai Veloster 2011-2017 Service Manual has the majority of technical information regarding sensors and whatnot. That site is for the N/A but much of the information carries over to the Turbo. Keep in mind there are two sensors you need to check: one on the front of the intake manifold and one on the cold side of the intercooler.

Once again, take it with a grain of salt, but here's my personal take: your turbo is probably bad. Deferred maintenance on these cars is PARTICULARLY damaging, especially oil changes. When I got my VT (and was a lot worse educated on it) it had not been taken particularly well care of. Oil grime visible inside of the valve cover, too long change interval, wrong oil grade, etc. Nothing fixed the underboost code until the turbo was fully replaced. I certainly hope that's not what you're looking at but keep it in mind. Replacing all these sensors (that might not even be bad) will cost you a ton on top of replacing the whole turbo assembly, if that ends up being your issue.

Also worth noting my underboost code would only pop on occasion under fairly high load. Car would go into limp mode and then revert to normal on restart. I drove it for a good long while during this, including while "limping" and the car seems to still be okay.

What other codes are popping? Do you have a code reader to look for yourself? What was the oil change interval and what grade of oil / kind of filter are you using?
 

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Underboost code can also be caused by loose charge pipes, faulty solenoids and a torn BOV.
 

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As someone who just recently had a turbo failure... P0299 and a loss of power sounds exactly like what just happened to me. If you're not seeing white smoke out of the exhaust or pcv systems then that's a better sign. Check the hot pipe (hose from turbo to intercooler) for oil too. If you really want to get your hands dirty you can take off the down pipe or the turbo inlet pipe and check for any wiggle with the shaft.

I don't think you need to check those sensors or anything else as they normally read completely different codes.
 
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Discussion Starter · #6 ·
In my (completely anecdotal, take it with a grain of salt) experience, typically the underboost code only pops when there's complete turbo failure. You can pop the bumper off to look for damage to the intercooler and other intake tubing yourself, or run a smoke test to pressurize the entire intake system which will show you the same thing.

You can check voltage and resistance across those sensors yourself. Hyundai Veloster 2011-2017 Service Manual has the majority of technical information regarding sensors and whatnot. That site is for the N/A but much of the information carries over to the Turbo. Keep in mind there are two sensors you need to check: one on the front of the intake manifold and one on the cold side of the intercooler.

Once again, take it with a grain of salt, but here's my personal take: your turbo is probably bad. Deferred maintenance on these cars is PARTICULARLY damaging, especially oil changes. When I got my VT (and was a lot worse educated on it) it had not been taken particularly well care of. Oil grime visible inside of the valve cover, too long change interval, wrong oil grade, etc. Nothing fixed the underboost code until the turbo was fully replaced. I certainly hope that's not what you're looking at but keep it in mind. Replacing all these sensors (that might not even be bad) will cost you a ton on top of replacing the whole turbo assembly, if that ends up being your issue.

Also worth noting my underboost code would only pop on occasion under fairly high load. Car would go into limp mode and then revert to normal on restart. I drove it for a good long while during this, including while "limping" and the car seems to still be okay.

What other codes are popping? Do you have a code reader to look for yourself? What was the oil change interval and what grade of oil / kind of filter are you using?
No other codes according to the dealer, Synthetic oil, not sure on filter or change intervals(probably not frequent enough)/ They didn't clear codes but I think I will disconnect the battery later today and see I can get the codes to clear and see if they show up again. Thx for the link!

So it sounds like it's ok if she drives it while I work this out?
 

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Underboost code can also be caused by loose charge pipes, faulty solenoids and a torn BOV.
This makes SENSE, but in my experience, does not happen (at least on my car). I've driven hundreds of miles with absolutely NO boost (faulty resonator connection and no jack to fix it) without ever throwing an underboost code. Turbo spooled fine (had the fun spooly noises to prove it) but no boost ever even made it to the intercooler. No underboost code. Only happened back when I had the turbo failure. Probably different for other people, though. Just my experience /shrug

Like I said, you can check the sensors just to rule them out, but I really don't think it's going to be your issue here. Worth checking just in case it DOES happen to fix your issue.

Oil change interval should be, at minimum, 5w30 full synth with OEM filter every 3k miles. That frequency is pretty non-negotiable to keep the vehicle running good. You can go a little lower on the winter side and higher on the hot side (I use 0w40) but that's a good starting point.

When I had turbo failure with an underboost code, I drove it for a good while before the issue was fixed. I can't guarantee your car will be fine, but MINE was.
 

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P0299 will be from a boost differential of more than ~4 psi from what the ecu thi ks the car should be making. So check for boost leaks. Nothing else needs to be checked until you're sure no boost leaks. If you get no power due to code, shut car off and power is back, this is good sign no mechanical or electrical issues and solely a boost leak.

Common areas are the hot pipe leaking somewhere and the BOV diaphragm having small tears/holes.

Report back ill gladly walk you through the fix.
 

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Discussion Starter · #9 ·
P0299 will be from a boost differential of more than ~4 psi from what the ecu thi ks the car should be making. So check for boost leaks. Nothing else needs to be checked until you're sure no boost leaks. If you get no power due to code, shut car off and power is back, this is good sign no mechanical or electrical issues and solely a boost leak.

Common areas are the hot pipe leaking somewhere and the BOV diaphragm having small tears/holes.

Report back ill gladly walk you through the fix.
awesome appreciate the help, how do you check for leaks on this pipe? Just check fittings are secure?
 

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awesome appreciate the help, how do you check for leaks on this pipe? Just check fittings are secure?
That'll be part of it. The only real fool foolproof way is to fill the intake with smoke and then pressurize it, which will force the smoke to escape through any leaking areas. You can also spray soapy water on the intake system while the car is running. If you spray it over a boost leaking section, air bubbles will form in the water.

If you don't have an air compressor and can't find anything otherwise, you might have to just remove sections to thoroughly inspect. I just recently fixed a hot pipe leak that I couldn't find until I actually pulled the hose off and got a good look at it in the light.

If you pull off the blow off valve (you'll have to remove the bumper and unbolt it from the top of the intercooler, you can test it by fully depressing the diaphragm and then sealing the top hose barb with a finger. When you release the diaphragm, it should extend slightly and then hold position against the vacuum generated by your finger blocking flow. When you release your finger, the diaphragm should extend the rest of the way.
 

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I suggest remove the pipe, clean all sealing surfaces, inspect all components for any defects that may cause leaks, then reinstall. During reinstall I'd use a better clamp than a spring clamp on the resonator section that the oem provides but this is not needed if everything is installed properly.
 

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I have had that experience with the code. Especially if the car isn’t making what it wants lol
 

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Discussion Starter · #13 ·
update from yesterdays work..... no success in finding the leak, I need more help in diagnosing where the leak is. We made the Home Depot boost leak test kit which allowed us to push in compressed air at the turbo. Not sure if we should have capped the line anywhere else or what but air flowed freely into/out of the system. We sprayed all connections with soapy water and got nothing showing a leak. my guess now after thinking about it is we should have capped the line somewhere else... I just don't know much about turbos.
See my video link of what it sounds like when we push air in from the compressor, there is a thud and then the air seems to flow even faster, is this the waste gate opening/closing(after we stop pushing air)?

Posting a pic of the intercooler that looks beat to hell IMO, I'm sure that could be an issue also. Took the BOV off and compressed it, put my finger over the end and it held in place so no issue there, rubber seems to be in good shape.
106830


Whats the bulge in this line, see pic., check valve? The line has some cracking in and probably needs to be replaced.
106831

106832


and a pic of my dads DeLorean :) for sale in you know anyone $65K
106833
 

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Yeah that check valve is normal for the evap line
 

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Boost leak test requires it holding pressure and you knowing what the pressure is as well. So yes it needs to be capped. Once under pressure you need to see it leaking down and sometimes you can hear it. Other times it requires soapy water or smoke to find it.
 

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Discussion Starter · #16 ·
Boost leak test requires it holding pressure and you knowing what the pressure is as well. So yes it needs to be capped. Once under pressure you need to see it leaking down and sometimes you can hear it. Other times it requires soapy water or smoke to find it.
ok so where to cap the other end if we are forcing air in where I show in my video?
 

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The cold pipe outlet is #1 or intercooler outlet is option #2
 
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