Boost Spikes - turbo actuator and boost valve questions

I've been searching and reading so many threads about boost that it's getting exhausting. I still have questions, so hopefully some wise folks can chime in.

Background:
The car is a '99 Beetle, ALH engine. I'm pretty sure it was stock when I bought it. After connecting a boost gauge to the upper intercooler hose a few months ago, I saw that my boost spiked to 19 psi max and leveled off around 14 at WOT (don't know why we use that term when these cars don't have throttles). After some reading, this seems pretty normal.

After getting DLC 520s installed, my boost spikes to around 22 psi max, and levels off around 14. The turbo can only handle 18.5 psi sustained, so the increase concerns me a bit. I'm going to RocketChip to get RC3 in about two weeks, and I know the tune will increase boost, so I called Jeff. I asked about a boost valve, but he called it a band-aid and said that even if it was installed, the spring is tuned to a certain psi and can only operate in a dynamic fashion. Thus, if sustained overboost occurred, a boost valve would stop relieving boost eventually and could not adequately protect the turbo. He said I should address the underlying problems instead (ie, turbo actuator, vanes, etc).

So, questions:
1. If the boost valve is really just a relief valve with a spring that gets compressed at a certain pressure, why won't it stay open as long as overboost is still occurring? If that's true, what's the hesitation with using one? Surely installing one is far simpler than disassembling the turbo to clean out carbon from the vanes, etc.
2. If I choose to use a boost valve, where can I purchase one that does not have a vent hole? I know a vent hole is not desired for these turbos/actuators. Why?
3. If I decide to adjust the actuator, do I only adjust the stop, or is there more adjustment that can be made? Will this only affect the max boost, or will it decrease my sustained boost as well?
4. Is it straightforward to access the actuator on the Beetle's turbo, or will I have to remove things to get to it?
5. If it's carbon on the turbo vanes that's slowing the turbo response rather than a misadjusted actuator, can some of that be burned off by revving near redline and keeping the EGTs high for an extended period of time?

Thanks for any help.

Short answer... Yes.. Yes. Yes. No. Yes. Maybe. Lol.

Yes your turbo vanes are probably jamming up causing the delay.

Yes you'll need to replace your turbo or at the least take it apart and clean the vanes.

Yes you should check your actuator movement.

No there's only the actuator rod you need to adjust. Don't move the stops. Rod should start to move at 3-5inhg, full stop at 16-18inhg. With the actuator disconnected, it should have almost no resistance to move.

And yes a boost valve is a bandaid. It doesn't limit boost pressure, but limits the vacuum to the actuator to lessen the boost, but it will creep back up.

No there's nothing fancy you need to take off to get access to your actuator. Just jack up the front end and put on stands, you'll see it easy.

As for the vent hole on the boost valve, that I don't know anything about.

Make sure that the "vent" line / hose that gets clean air from the side of the air box is not restricted. This is what allows the N75 to release.

There is another band-aide you can do... if you Tee into the boost and run it to the N75 (instead of the vent), it will move the actuator back to rest faster than just the internal spring. I've used it along with a boost limiter ("dawes device") - to tune in my max PSI to 24 on my BEW. It was supposed to be a temporary thing until I got my 3bar MAP installed and retuned, but it works so well I've left it for years.

Hmm

I don't have the time/resources at the moment to fight through all the rust to get my turbo off. So with that option out the window...

Regarding adjusting the stop on the turbo, in certain situations moving the stop is the proper treatment, right? Why not here?

And could you explain why the boost valve will allow the boost to creep back up? My understanding is that a certain boost pressure (determined by the spring force) will open the valve. At that point, boost pressure will be sent to the vacuum side of the actuator. This opens the vanes in the turbo, thus decreasing its rpm and the boost it can generate. This is essentially the same thing the N75 does, right? I would assume the boost valve won't close till the pressure drops, so why is it not functioning as effectively as the N75?

Without fully understanding the creep issue you mentioned, is it possible this is a result of using the wrong boost valve? That is, one with an open vent rather than one with the vent plugged?

gforce, thanks for the idea about sending boost pressure to the N75. Is there a chance this will decrease its lifespan?

And if all of this won't stop the boost fast enough, as a last resort, why not just stick a standard pressure relief valve into the lower intercooler hose? Extra boost would get dumped to atmosphere. Obviously this isn't how the system is designed, because the turbo would still be "trying" to generate boost. But does that really matter if the boost is sent overboard? Will the turbo overspeed?

Also, here is the boost valve Kerma sells.

The site says, "The BoostValve has always had a very small vent hole to release any air trapped in the waste-gate line after boost pressure drops... For vacuum controlled waste-gate setups such as the VW VNT turbo use a non-vented cap for a completely sealed valve." I guess I'll contact Kerma to see whether that cap is included with the kit.

My advice, listen to Jeff. Clean your turbo and check the adjustment.
The spike is the turbo spinning out of control, if the vanes are sticky,
the ECU can't brake it to bring the vanes under control fast enough.

I had the same problem recently, turned out the locknut on the actuator
was loose. Reset to 5psi, no more spikes.

I'm confused (happens). You have a boost valve, N75 and you have a throttle. Are you wanting to troubleshoot just the high boost value? I don't believe that value represents anything dangerous, does it set a CEL? Howz it run? You will need to remove the lower engine cover and put the car up to access the actuator, might be worth checking it's operation, maybe evaluate the turbo.

BeetleDragon737 said:

Hmm
I don't have the time/resources at the moment to fight through all the rust to get my turbo off. So with that option out the window...
Regarding adjusting the stop on the turbo, in certain situations moving the stop is the proper treatment, right? Why not here?

Click to expand...

I don't think I've ever seen someone need to adjust that stop on an existing turbo. Unless someone messed with it - it shouldn't need adjusting. The turbo I just removed off my 03 was a little sticky and had bunch of play due to wear in the VNT internals.

BeetleDragon737 said:

And could you explain why the boost valve will allow the boost to creep back up? My understanding is that a certain boost pressure (determined by the spring force) will open the valve. At that point, boost pressure will be sent to the vacuum side of the actuator. This opens the vanes in the turbo, thus decreasing its rpm and the boost it can generate. This is essentially the same thing the N75 does, right? I would assume the boost valve won't close till the pressure drops, so why is it not functioning as effectively as the N75?
Without fully understanding the creep issue you mentioned, is it possible this is a result of using the wrong boost valve? That is, one with an open vent rather than one with the vent plugged?

Click to expand...

That kind of boost valve is designed for a wastegated turbo, which the VNT does not have. It gets used in a different manor on a VNT turbo but will only work if the VNT/N75, etc is working correctly already. The N75 is not a ON/OFF only - it is a fully variable vacuum controller so the VNT can be in any position, not just fully one way of the other.

BeetleDragon737 said:

gforce, thanks for the idea about sending boost pressure to the N75. Is there a chance this will decrease its lifespan?

Click to expand...

I've put probably 100k miles with it this way. I still recommend people get their hardware and tune straightened out instead of doing what I did, but it works well for me.

BeetleDragon737 said:

And if all of this won't stop the boost fast enough, as a last resort, why not just stick a standard pressure relief valve into the lower intercooler hose? Extra boost would get dumped to atmosphere. Obviously this isn't how the system is designed, because the turbo would still be "trying" to generate boost. But does that really matter if the boost is sent overboard? Will the turbo overspeed?
Also, here is the boost valve Kerma sells.
The site says, "The BoostValve has always had a very small vent hole to release any air trapped in the waste-gate line after boost pressure drops... For vacuum controlled waste-gate setups such as the VW VNT turbo use a non-vented cap for a completely sealed valve." I guess I'll contact Kerma to see whether that cap is included with the kit.

Click to expand...

If you bleed off boost but allow the turbo to keep trying to make it, you risk overspeeding it. See above about wastegate...

BobnOH said:

I'm confused (happens). You have a boost valve, N75 and you have a throttle. Are you wanting to troubleshoot just the high boost value? I don't believe that value represents anything dangerous, does it set a CEL? Howz it run? You will need to remove the lower engine cover and put the car up to access the actuator, might be worth checking it's operation, maybe evaluate the turbo.

Click to expand...

No check engine light. It runs ok. I haven't checked VCDS for any codes yet. I know that max sustained boost for the VNT-15 is 18.5 psi, so I'm concerned that having overboost at 20+ psi for anything other than a moment will damage my turbo. I'm definitely going to check the actuator operation when I can. My guess is it will stick, so the 5 psi - 18 psi range will probably be more like 10-25 or something.

gforce1108 said:

That kind of boost valve is designed for a wastegated turbo, which the VNT does not have. It gets used in a different manor on a VNT turbo but will only work if the VNT/N75, etc is working correctly already. The N75 is not a ON/OFF only - it is a fully variable vacuum controller so the VNT can be in any position, not just fully one way of the other.

Click to expand...

My understanding of the N75 is a little lacking, but from diagrams posted frequently on the forums, the way I described the operation of the boost valve is correct, yes? It tees into the vacuum line between the N75 and the VNT actuator and ports boost pressure to that line if overboost occurs.

BeetleDragon737 said:

My understanding of the N75 is a little lacking, but from diagrams posted frequently on the forums, the way I described the operation of the boost valve is correct, yes? It tees into the vacuum line between the N75 and the VNT actuator and ports boost pressure to that line if overboost occurs.

Click to expand...

That is correct - search for "dawes device TDI" for better information on how it relates to VNT turbos. But it's still assuming that the VNT is working properly. It doesn't matter how much boost you put to the vacuum actuator if the VNT is sticky. I still can peg my gauge at 35psi sustained if the VNT gets sooted up.

gforce1108 said:

It doesn't matter how much boost you put to the vacuum actuator if the VNT is sticky. I still can peg my gauge at 35psi sustained if the VNT gets sooted up.

Click to expand...

This must be if it is very sooted up, right? If it's a sliding scale, with a little soot, it won't respond quite as fast. But if there's a lot of soot, it won't open the vanes at all, no matter what you do? The idea with the boost valve is to tell the actuator, "NOW", and with the increased pressure against the diaphragm, sticky vanes will yield more easily. Yes?

Kerma's page on the boost valve says this,
"Boost spike can be a major issue with the VW TDI VNT turbo. Back pressure or excess fuel can cause the boost to rise faster than the turbo's vanes can react. With age soot tends to accumulate and cause restrictions in the catalytic converter or exhaust Spike and surge can cause the ECU to react by pulling out timing from the motor, this results in lower torque output. By installing the BoostValve as shown above this excess boost can be prevented.
The BoostValve is not used to raise max boost but to control spike/surge and effectively give better control of the turbo's wastegate. No more surging or dangerous boost spikes." (I'm assuming by "wastegate", they really mean "vane actuator", as the VNT has no wastegate.)

And regarding testing the actuator, if I find that the actuator does not move and stop at the proper vacuum pressure, does that mean my actuator is bad, or does it mean my turbo vanes are sticky? How do I differentiate between those?

Bite the bullet and fix your turbo & actuator. Buy a used one for
$2-300, clean it up, and then swap it out.

You can talk yourself into the Kerma marketing if you want,
but it will only work for a while. Your turbo will grenade,
or just die, from what you've told us, it's already got some
problems.

Good luck with your decision.

BeetleDragon737 said:

This must be if it is very sooted up, right? If it's a sliding scale, with a little soot, it won't respond quite as fast. But if there's a lot of soot, it won't open the vanes at all, no matter what you do? The idea with the boost valve is to tell the actuator, "NOW", and with the increased pressure against the diaphragm, sticky vanes will yield more easily. Yes?
Kerma's page on the boost valve says this,
"Boost spike can be a major issue with the VW TDI VNT turbo. Back pressure or excess fuel can cause the boost to rise faster than the turbo's vanes can react. With age soot tends to accumulate and cause restrictions in the catalytic converter or exhaust Spike and surge can cause the ECU to react by pulling out timing from the motor, this results in lower torque output. By installing the BoostValve as shown above this excess boost can be prevented.
The BoostValve is not used to raise max boost but to control spike/surge and effectively give better control of the turbo's wastegate. No more surging or dangerous boost spikes." (I'm assuming by "wastegate", they really mean "vane actuator", as the VNT has no wastegate.)
And regarding testing the actuator, if I find that the actuator does not move and stop at the proper vacuum pressure, does that mean my actuator is bad, or does it mean my turbo vanes are sticky? How do I differentiate between those?

Click to expand...

They are copying someone else's verbiage related to the boostvalve - it looks like there used to be links in there to hooking one up on a VW VNT TDI. The search I recommended on the dawes device will be more relevant to a VNT. It's designed for a little extra insurance, not a "fix".

If you haven't watched some youtube videos on the VNT internals - look them up. I'm not sure that you are thinking about how it works correctly (sounds like you are still thinking more like a wastegate) since you mention it "opening" the vanes. It's just redirecting the internal flow.

As far as mine - If I drive it gently for too long, typically in the winter with snows (it'll spin into 3rd), it gets sooted up. I hook up my trailer (~1000lbs or so total) and take a full throttle run up a long grade. Cleans it right out. The boostvalve does not prevent the overboost.

The VNT actuator is a pretty simple part - 99% of the time it'll work or leak. I have had one be a little crusty inside and still work. It is very easy to tell if you remove the clip and disconnect the VNT arm from the actuator. The VNT should move fully with very little effort. A new OEM actuator is like $115. I haven't bothered with a chinesium ebay/amazon special.

An update. I checked the actuator under vacuum today. It started moving right at about 4" Hg and stopped moving right around 19". When I rapidly released the vacuum, the actuator arm smoothly extended out again as the pressure increased with no sticking whatsoever. So the actuator isn't the problem. The vanes could have slightly higher friction than desired, so maybe that's causing some boost spikes. But if they do, it's minimal, and it was too cold and wet outside to continue messing around with it.

At the moment, I'm thinking my boost spikes are likely caused by crazy soot buildup in my intake manifold. When my shop cleaned my EGR a few years back, they said there was a ton of gunk in the EGR. If there's buildup in the intake, the flow would be restricted, causing back pressure. I'm not prepared to take that off now either. I'm considering the Dawes device a temporary fix.

gforce1108 said:

If you haven't watched some youtube videos on the VNT internals - look them up. I'm not sure that you are thinking about how it works correctly (sounds like you are still thinking more like a wastegate) since you mention it "opening" the vanes. It's just redirecting the internal flow.

Click to expand...

Here is the video sometimes referenced for the VNT. When vacuum is applied, the gaps between the vanes decrease. Some describe that as closing. When vacuum is released, you could say they open.

gforce1108 said:

As far as mine - If I drive it gently for too long, typically in the winter with snows (it'll spin into 3rd), it gets sooted up. I hook up my trailer (~1000lbs or so total) and take a full throttle run up a long grade. Cleans it right out. The boostvalve does not prevent the overboost.

Click to expand...

If I understand it right, the only reason overboost could still occur with a boost valve is because the vanes are not just "sticky"; they are "stuck". If the vanes are stuck, even with the boost valve open and full boost pressure hitting the actuator diaphragm, the vanes do not want to move. Hence, they will remain in the high boost / closed position and the turbo will produce the maximum boost it is capable of. Does this seem right to you? After you do your full throttle run and blast the soot out, is it still capable of overboosting like this?

After some more reading and looking around, I found this thread describing how oven cleaner can be used to clean soot from the turbo. That would be much easier than taking the whole thing off!

And here's a great tutorial from myturbodiesel on vane/actuator testing, diagnosis, etc.

There's also this massive thread describing a number of causes of overboost, but specifically related to limp mode.

Regarding overboost and limp mode as opposed to boost spikes... Why would a vacuum leak cause overboost? Vacuum is what positions the vanes to create boost in the first place. If there is a leak, that should decrease boost, not increase it, yes?

Lack of vacuum keeps the vanes in the opened, full boost position. At low rpm the vanes will be closed or partially so as shown in your 12 second video. The vanes will open further at higher rpm's as the vacuum will decrease. So if the vacuum is leaking you will get full, over boost at the lower rpm's which you don't want. The actuator on my turbo could not hold vacuum and as a result I was getting full boost at low rpm's which resulted in sluggish performance.

JB05 said:

Lack of vacuum keeps the vanes in the opened, full boost position. At low rpm the vanes will be closed or partially so as shown in your 12 second video. The vanes will open further at higher rpm's as the vacuum will decrease. So if the vacuum is leaking you will get full, over boost at the lower rpm's which you don't want. The actuator on my turbo could not hold vacuum and as a result I was getting full boost at low rpm's which resulted in sluggish performance.

Click to expand...

Well, this is confusing. You say the "full boost position" is when the vanes are open. Why do you say that? As this video shows, for a given rpm, closing the vanes will create more boost (that is, higher turbo speed). At low rpm, you want the vanes closed, because you don't have high exhaust flow rate already. Closing the vanes forces the gases through smaller channels and provides that higher flow rate at a more dramatic angle which will drive the turbo speed up. At high rpm, to prevent overboost, the vanes open. This allows the already high-flow-rate exhaust to pass through the vanes without accelerating too much and overwhelming the turbo.

If the actuator cannot hold vacuum, this would lend it to keeping the vanes partially open. Thus, at any engine speed, the boost would be lower than desired, causing sluggish performance. Regardless of rpm, how would full boost cause sluggish performance (unless it triggers limp mode)? Higher boost pressures mean more air is being drawn in, and thus, more fuel can be requested by the ECU while maintaining efficient fuel/air ratios. More fuel should always result in higher power.

What is the misunderstanding here?