Boost Fluctuation.

[Denio24]

So I just got a podi boost gauge; don't know why I didn't get one sooner. I have noticed that many times it has occurred that under WOT the boost goes to the regular 1.4bar (20psi) but then fluctuates down to 1.0 bar (15psi) - sometimes lower - and back again to 1.4bar. This can happen as much as three times (didn't test it further as i don't want to drive too fast). So far it has happened to me in 2nd, 3rd, and 4th gear. Any explanation for this? Sometime this doesn't happen at all and the boost goes to 20psi max and tapers off like it normally should.

[Mlambrecht17]

Do your rpms fluctuate too? Tiptronic?


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[Denio24]

No they do not. manual.

[Charles.waite]

might have a leak in your intake piping? Or a bad N75. Or a misadjusted wastegate.

[Denio24]

what are symptoms of a wastegate that isn't adjusted properly? n75 was replaced and car was checked for leaks.

[BenMTL]

Do you feel boost letting go or is it just displaying as so on your guage? To me just sounds like a loose fitting on your boost guage or a boost leak on where ever you connected it to read boost pressure?

[Denio24]

I feel it 100%. During the fluctuation it pull stronger, then weaker, then stronger, etc.

[Charles.waite]

Why was the n75 replaced? Could point towards a loose wastegate.

[JDillon15]

I feel it 100%. During the fluctuation it pull stronger, then weaker, then stronger, etc.

I've experienced what you're talking about. I know if the waste gate is failIng, there will be play in it (i.e. You can move the rod)


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[Denio24]

Why was the n75 replaced? Could point towards a loose wastegate.

n75 was replaced as part of maintenance. Will try to get logs of the issue at hand here.

[Denio24]

Peak boost on the log is 2300 mbar or 33.36 psi. After conversions to atmospheric (33.36-14.5) it equals 18.86psi. Weird, this time it didn't fluctuate, but boost should be peaking at 20, no?

[Charles.waite]

Peak boost on the log is 2300 mbar or 33.36 psi. After conversions to atmospheric (33.36-14.5) it equals 18.86psi. Weird, this time it didn't fluctuate, but boost should be peaking at 20, no?

It would be good to see how actual boost tracks with requested boost. Also how the WG duty cycle tracks with the boost fluctuations.

[Denio24]

It would be good to see how actual boost tracks with requested boost. Also how the WG duty cycle tracks with the boost fluctuations.

Here is the full log:

[mfdk]

I don't mean to high jack this thread but Im going to take advantage of it rather then making another one. Do my boost numbers look ok on Stock 2.0t, no tune.

part 1


part 2


Here is at idle


Car always seem to pull fine, the only thing that got me worried is that when i came back from a 2hr highway trip, i popped the hood and the turbo exhaust housing, exhaust manifold and 034 hfc were red, not glowing but they were red.


Sent from Outer Space

[audi8844]

To OP, I had a very similar issue with about 80k miles on the car (also 2008 manual). I had a Uni Stage 1+ tune for ~40k miles prior. I noticed some slop in my oil (not much). I was originally worried this was head gasket, but there was no obvious drop in coolant or browning of the coolant. Then Ray @ RAI had suggested to smell the oil and see if it smells of gasoline, as the HPFP could be leaking via the internal seal. It certainly did, but not too strong. I wanted to upgrade my HPFP and work my way to stage 2 with HPFP, so I made the switch to JHM HPFP. Since installing the fuel pump, this behavior went away. When I knew this was fixed, I also installed JHM software (awesome, but that's another subject). People were suggesting it was N75 or boost leak, but these were checked and not the cause. Not to say this is definitely the case, but maybe you can swap your HPFP with someone else to see if it fixes the problem, prior to purchasing a replacement.

[AJacksA4]

I had the same issues with my REVO software. I never solved the issue as I switched software, but I always suspected it to be fuel cuts from the HPFP

[mfdk]

Anyone care to share some knowledge on my situation with my stock turbo mentioned above...

[Denio24]

I don't mean to high jack this thread but Im going to take advantage of it rather then making another one. Do my boost numbers look ok on Stock 2.0t, no tune.

part 1


part 2


Here is at idle


Car always seem to pull fine, the only thing that got me worried is that when i came back from a 2hr highway trip, i popped the hood and the turbo exhaust housing, exhaust manifold and 034 hfc were red, not glowing but they were red.


Sent from Outer Space

Logs look fine; thing is you're not really hitting any boost. So I dont really know what you're asking. However a glowing cat and manifold can mean that your cat is clogged.

[mfdk]

Logs look fine; thing is you're not really hitting any boost. So I dont really know what you're asking. However a glowing cat and manifold can mean that your cat is clogged.

Everything is stock beside the 034 hfc, i'm just trying to understand what a stock k03 turbo on non tuned engine should be producing as far as boost, I never had a turbo engine and I want to know if my turbo is working efficiently.

Thanks

[Denio24]

15 psi max if i'm not mistaken. Remember that your engine reads pressure in absolute units, to subtract 14.5 psi after converting millibar to psi.

You should be seeing max boost if you go wot around 2000-2100 in the vcds boost logs.

[mfdk]

15 psi max if i'm not mistaken. Remember that your engine reads pressure in absolute units, to subtract 14.5 psi after converting millibar to psi.

You should be seeing max boost if you go wot around 2000-2100 in the vcds boost logs.

So according to my math,

Actual boost pressure subtract by absolute pressure = mbar multiple by 0.0145 = psi

1400mbar - 1000 = 400 * 0.0145 = 5.8psi


correct..!

[Charles.waite]

Well ambient pressure depends on altitude. At sea level it should be 1 bar. For me, in Seattle, it's usually in the high 900 range.

[mfdk]

Well ambient pressure depends on altitude. At sea level it should be 1 bar. For me, in Seattle, it's usually in the high 900 range.

Where i live in South Carolina its 1000 but i have occasionally seen it in 900 range too.

[Charles.waite]

Yup. What I always do is create a third column and auto fill it with (actual - ambient) * (conversion factor for mbar to psi). Then do the same for requested. That way it's in psi and corrected for ambient so it's easier to see what's going on.

[mfdk]

Yup. What I always do is create a third column and auto fill it with (actual - ambient) * (conversion factor for mbar to psi). Then do the same for requested. That way it's in psi and corrected for ambient so it's easier to see what's going on.

Thanks a lot, will give that a try.

Cheers

[mfdk]

So today i ran another log under WOT but running in sport mode -Tip and i was boosting around 11psi which i think its the most you could get out of stock k03 without any tunes!


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[Charles.waite]

My stock manual b7 usually boosts around 12psi so that sounds about right to me.

[mfdk]

Thanks, based on some research thats the most the k03 can produce without any software or hardware tune.


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[esandes]

maybe a cracked turbo or flange.

[oVeRdOsE]

mine goes to 22psi until 5500-6000 rpm, then slowly get to 15 psi until I shift around red line.

Small turbo, I believe this is normal ?

[Charles.waite]

mine goes to 22psi until 5500-6000 rpm, then slowly get to 15 psi until I shift around red line.

Small turbo, I believe this is normal ?

If you're tuned, yea.

[oVeRdOsE]

If you're tuned, yea.

do you know of it's the turbo physic limitation or the tune itself for protection?

Normally a small turbo will not follow linearly the rpm VS air flow.
But the pressure should remain about the same. So I believe, the tune is made to protect the engine for high pressure on high revolution.

tks

[Charles.waite]

The k03s drop off like that because they can't flow enough at higher rpms. Basically they fall off the efficiency island.

15psi at redline does seem a bit low though. My 1.8t used to do that but they run out of juice even faster than the 2.0t does.