Questions about verifying the correct setting of stop screw on a VNT-17

[pyromancer]

I've had an issue with low end lag on my car since I have installed this turbo and tuned. Recently worked with a tuner to try to correct this issue a bit, as well as not meeting the requested boost, and the determination was likely something to do with my hardware. We were able to fix the not meeting requested issue. In working with them I made sure there was no boost leaks, vac leaks, made sure motion was good, cleaned the turbo, and tried adjusting the actuator arm shorter and longer multiple times without resolving things. I tried everything I could find to try short of messing with the stop screw. More recently I have started trading emails with a member here who is in the process of learning to tune in hopes he could point me to something hardware maybe I haven't checked. After reviewing logs, vac readings, and details about all the stuff I have tried to fix this issue he suggested the stop screw on my turbo maybe set incorrectly. The tuner also wondered if I had something wrong with my turbo, and in trying to figure stuff out myself, more then once I have wondered if my stop screw was off or something.

Turbo was purchased from a respected vendor years ago and I have never messed with the stop screw. Have always read you should not need to do it, and its not a great thing to do without a flow bench or Exhaust manifold pressure (EMP) gauges. As in it's an easy way to cause lots of damage to your engine or turbo. Looking for a way to check to see if I am set correctly it seems like you could pull the turbo apart and measure the gap in the vanes to set it. Or in searching here I have seen a few posts saying if you need to do it you can "Adjust set screw between 2 to 4 psi at 2000rpm when engine are hot with full vacuum on actuator (bypass N75)". Would love more info/details on that if its a viable way to check or set the stop screw. Under load? In neutral? Measuring with a boost gauge or just looking for couple hundred mbar while measuring block 11? I have questions.

So has anyone ever adjusted the stop screw without EMP gauges or a flow bench? Is there a relatively safe way to check the stop screw position without pulling and taking the apart the turbo? Seems like I have 4-5 threads showing but from reading not even sure that's useful, as length may not be a good measure due to variation in the turbo inner parts can throw that off. I'm tempted to see how mine is set vs. the 2000rpm thing above but again would love more detail on the procedure for that. Have also thought about backing the screw out half a turn and seeing if it might fix some of my lag but I'm kind of scared and really do not want to damage the car. Everything I have read has put some fear in me about messing with the stop screw. Car is an 01 ALH, VNT17, 1019 injectors, 10mm pump, Stage 4 tune.

 

[TurboABA]

So if you are suspecting the adjustment is the issue, why not measure and record the current setting, and then simply adjust it (slightly ~1/8 turn) to allow less VNT travel, and see if you're getting any improvements? If you have VCDS and are monitoring\logging things, you should be able to see if you're improving or not and not get to a point where you're in danger of hurting stuff.
I'm sure you already know all this, but it gives some indication of what could "fail" or cause issues.

 

[pyromancer]

So if you are suspecting the adjustment is the issue, why not measure and record the current setting, and then simply adjust it (slightly ~1/8 turn) to allow less VNT travel, and see if you're getting any improvements? If you have VCDS and are monitoring\logging things, you should be able to see if you're improving or not and not get to a point where you're in danger of hurting stuff.
I'm sure you already know all this, but it gives some indication of what could "fail" or cause issues.

It's a good video, have watched it a few times, as well as reading the Kerma turbo troubleshooting guide, and the turbo guides on myturbo diesel. They have that video linked over there as well.

As to marking the stop screw and just trying to adjust it. I would be shortening the stop (backing it out) to allow more travel of the rod. Vanes tighter so it spools faster down low. Less VNT travel, or lengthening it, as you mentioned wouldn't worry me as much. As many of the warnings about damage I see talk about vanes getting too close and bad things happening. I also don't know how small of an adjustment would affect their position. Warnings about grenading turbos or welding vanes tip to tail have me scared to try it without at least talking to someone more experienced. I would assume 1/8th or even 1/2 a turn would likely still be safe, I'm not sure how small of an amount I could go and still see change either, I am hoping someone has done this before and can give me some real world advice mostly.

If anyone has more insight on a way to test it's position without just blindly adjusting, I'd love to hear it.

Digging around I've seen a few things similar to post #12 on this thread now https://forums.tdiclub.com/index.php?threads/brand-new-gt1749vb-huge-turbo-lag.491184/ "With hot engine at neutral, no accessory on (A/C, light, fan...), turbo actuator plug on full vacuum, at 2000rpm, the turbo pressure rise to 2-4 psi if stop screw are ok (dont ajust stop screw if you are not completly sure of all other thing are ok)" Which I think I might try now that I have some more details. A test like this really wouldn't hurt or change anything, just throw the vac feed from the N75 onto the turbo line and in neutral look at boost at 2k rpm. I'm just not sure how accurate of a test this is, as most of the mentions I have seen about it are by the same guy.

Adding I am also finding stuff referencing VCDS basic settings test of block 11 with the car at 1400 rpm should show a change of 80-250mbar as a test for the stop screw as well. It seems like this maybe valid on a BEW but I am not sure it is on an ALH. I found this https://www.myturbodiesel.com/d2/1000q/a5/turbo-response-adjustment-tdi.htm which details under procedure much of what I was finding referenced, again this is for BEW and BRM. The TLDR says performing the test at 1400rpm should see 80-250mbar change. It seems with the BEW VCDS even sets the idles up to 1400 and you can just watch it. I'm pretty sure on the ALH the test just toggles the N75 with the idle unchanged. At least that is what I have noticed when performing the test, possibly I didn't wait long enough? I did let it switch a good 6-7 times... I am curious if I should be seeing the same 80-250mbar if I slowly manually reved up and held at 1400rpm during this test though. Has anyone done that on an ALH or mind giving it a try and sharing results?

 

[TurboABA]

So you've already verified that all moves freely and you don't have anything binding, etc?

 

[pyromancer]

So you've already verified that all moves freely and you don't have anything binding, etc?

Yup removed the rod made sure the arm moves as it should. Even tried chemically cleaning the turbo on the off chance it was somehow gummed up a bit and I just wasn't feeling it. Hell I have even tried replacing all the gaskets on the intake and exhaust manifold on the off chance I had some leak I wasn't finding. Troubleshooting keeps coming back to some kind of issue with fueling, or an issue with the turbo itself.

 

[burpod]

https://forums.tdiclub.com/index.php?media/20220124_130117-jpg.145202/

Fwiw, That's where I set my wife's stop screw in her vnt17 a year or two ago, after it somehow fell out. Threads were messed up so retapped for a 6mm bolt. It's probably a bit too short, but it's ok . No crazy overboost problems... But I haven't spent a whole lot of time getting things just right on it. I may remove one of my spacer washers and test things out more with vcds but I've loaned it to my brother

 

[TurboABA]

Have you applied "manual" vacuum to it to see if you're anywhere close to the "specs"?

Adjust the actuator rod length such that it begins moving with 3-5inHg of vacuum and comes into contact with the stop just as 18inHg of vacuum is applied to the actuator.

 

[pyromancer]

Have you applied "manual" vacuum to it to see if you're anywhere close to the "specs"?

Well the specs are for adjusting the rod, so yes I have have the rod at spec. Right now it starts to move at 3-4 and hits the stop at 18-20. At idle the lever is resting on the stop screw.

As I understand things, and as the video you posted supports, changing the position of the stop screw would change when the rod hits the screw. At one point I had the tuner have me go way shorter on the rod until I was hitting the stop at less than 15, still with low end lag. If I had adjusted the stop screw out/shorter at that point I could have made it be in spec as well. I did not do this since the stop screw should be set correctly. The spec is for the rod, and only works if the stop screw is set correctly, as the stop screw is setting the position where the vanes are most closed, the rod can't affect that, from what I have read this should be a physical 1.6-2mm gap between them. If that gap is too small (stop screw too short) too much EMP and things are really not good, if that gap is too big (stop screw too long) it can cause lag at low RPMs. Stop screw is typically set at factor with a flow bench or sometimes on car but with the use of an EMP gauge. I am trying to determine if mine is set correctly, without pulling the turbo, disassembling and measuring the vane position.

 

[TurboABA]

So if you've verified the rod setting, then put a gauge on your N75 to ensure that it is indeed supplying the expected amount of vacuum.
The ECU is using that to "control" the vanes... so if you're not getting the correct supply, you wouldn't get the correct movement of the actuator.
Do you see the actuator moving fully when doing N75 output tests with VCDS?

 

[pyromancer]

So if you've verified the rod setting, then put a gauge on your N75 to ensure that it is indeed supplying the expected amount of vacuum.
The ECU is using that to "control" the vanes... so if you're not getting the correct supply, you wouldn't get the correct movement of the actuator.
Do you see the actuator moving fully when doing N75 output tests with VCDS?

Please see original post. I realize you are trying to help, but you are telling me to try things I have already tried and tested for without helping in regard to the original questions about the stop screw. Logs have been pulled and looked at for everything, multiple times. Vac to N75 at idle is 29, Vac form N75 to turbo at idle is 19, no leaks, have mechanically tested that actuator has full smooth motion... Output test on N75 rod has full travel and goes from 0 vac to 24... N75 has been replaced completely with a brand new unit with no change to behavior... Here is what the n75 does for vac output during a 3rd gear pull (this gauge reads about 1.5 low, tested with my mightyvac), but yeah we looked at that too https://photos.app.goo.gl/KNptnGkZ5ACzZW2YA

 

[TurboABA]

Well, if you want to take that approach, I read your post and it says that IT'S ALWAYS been like this.... thus, we can safely assume that your snail has been crap ever since the beginning. So, your turbo is incorrectly spec'd for the low end\spool you're after.

Good luck, and read this, if you haven't already.

Diagnosing and Fixing Limp mode for A4 1.9TDI [low power troubleshooting]

Diagnosing and Fixing Limp mode for A4 1.9TDI By Canadian Grizzly Read the entire post prior to jumping to conclusions. This is a general overview on how to diagnose and fix a A4 1.9TDI that goes into “limp” mode due to an overboost of the turbo. While I’m by no means an expert I’ve gleaned...

forums.tdiclub.com

 

[pyromancer]

Well, if you want to take that approach, I read your post and it says that IT'S ALWAYS been like this.... thus, we can safely assume that your snail has been crap ever since the beginning. So, your turbo is incorrectly spec'd for the low end\spool you're after.

Good luck, and read this, if you haven't already.

Diagnosing and Fixing Limp mode for A4 1.9TDI [low power troubleshooting]

Diagnosing and Fixing Limp mode for A4 1.9TDI By Canadian Grizzly Read the entire post prior to jumping to conclusions. This is a general overview on how to diagnose and fix a A4 1.9TDI that goes into “limp” mode due to an overboost of the turbo. While I’m by no means an expert I’ve gleaned...

forums.tdiclub.com

Yes, I have had this issue since installing the turbo, injectors, and tune that can utilize them. I have also read that thread as well as this one https://www.uk-mkivs.net/threads/vnt-tdi-turbo-how-to-adjust-actuator-cure-boost-problems.34834/ Which is also great, and if you look at my posts above, I have tested all that stuff. "So, your turbo is incorrectly spec'd for the low end\spool you're after." Figuring out if this is the case is what this thread is about and what I am looking for ways to test for. After talking to tuners the other possible issue could be fueling, as in a weak/failing pump, which we will be looking at with logging, but does not exactly rule out the stop screw as a possible issue as well. Again I know you are trying to help, but we have covered the normal bases already. Triple checking myself, being asked by everyone I talk to to check the same stuff again... It's frustrating, and doesn't help me or answer my questions about stop screw, I have logs and videos of testing all of this stuff now, happy to DM them to you as I have done with others. This issue does not seem to be caused by the typical suspects. I don't have another car to compare to myself, but in talking to others the consensus after looking at my 011 logs is I seem to have a lot of lag. According to burpod above I have more lag with my vnt-17 than he has seen on cars with larger turbos. We are squarely in things seem not right, but why? Again I have gone over the standard stuff that could cause lag from the help threads above, with myself and others, (vac, boost leak, n75 function, actuator, dirty turbo, etc.) and am trying to rule out the turbo/ stop screw setting being the issue, or part of the issue now. Maybe there is no way to really test for that aside from EMP gauges and or flow benches but might as well ask. Since I found some posts where people have adjusted there's E.g. https://forums.tdiclub.com/index.php?threads/stop-screw-adjustment-without-emp-gauge.377479/ I'm hopeful someone has some info...

 

[burpod]

the other thing to pay attention to in graphs like this, with being at such low rpm, the way this tune works, there is not as much lag as it appears to be in the graph. the torque limiter is limiting fuel in the lower rpm, but the specified boost is remaining the same as if fuel hadn't been lowered. if you were to see the graph of the specified boost for the actual amount of fuel injected, the "lag" would be less. however, there is still lag.

aside from possibly slight stop-screw adjustment, i don't think there's anything turbo, vacuum, or boost related wrong going on... i think if there's a hardware issue it's in the fueling.

 

[pyromancer]

"With hot engine at neutral, no accessory on (A/C, light, fan...), turbo actuator plug on full vacuum, at 2000rpm, the turbo pressure rise to 2-4 psi if stop screw are ok (dont ajust stop screw if you are not completly sure of all other thing are ok)" again found this test in this thread https://forums.tdiclub.com/index.php?threads/brand-new-gt1749vb-huge-turbo-lag.491184/

So I gave this a try. Figured it was an easy test and nothing to lose. This is what I did, plug the feed from the N75 directly into the vac line from the turbo so it had full vacuum, measuring block 011 in VCDS, bring the RPMS up to 2000ish and hold them there for a couple seconds so I can see any boost.

I'm definitely not seeing 2-4 psi at 2000 rpm. At Idle specified is 994.5 and actual is 1006.2 I'm at sea level so atmosphere should be about 1000mbar so that seems normal. At 2000rpm if my math is right I should be seeing 1140-1275ish mbar on my MAP actual if I am getting 2-4psi, and I am not. =(

To be able to see 150 mbar of actual on the MAP I had to rev it up to more like 2700rpm.

Does anyone know if this is an accurate test?

Or would anyone mind giving it a try with a properly set VNT-17 to let me know what their results are? It could help me out a lot.

 

[pyromancer]

Adding I have now tried raising the car to 1400 RPMs and watching for a change in boost of 80-250mbar during the block 11 test. See post #3 for more details on what I am talking about. Here is a video of the results. https://photos.app.goo.gl/h83CwrpVGkFFbdHz6 My change was only 59 mBar.

Would love if someone else with an ALH could give this a try and report back as well. I'd feel a lot more comfortable about adjusting that stop screw with at least more data from same engine.

 

[TurboABA]

Are your injectors clean? Were they calibrated before install? Have you run it fat or rolling coal for a long time until recently when you started to chase this down?

 

[TurboABA]

Perhaps some of this will interest you as well....

Injector Removal and Installation

www.dbwllc.net

 

[pyromancer]

Are your injectors clean? Were they calibrated before install? Have you run it fat or rolling coal for a long time until recently when you started to chase this down?

Injectors came form DBW LLC, pop tested and calibrated, followed all guides during install. Actually have copies of the DBW LLC PDF's saved because its handy to have the torque specs and process as I had hammer moded a couple times now trying different IQ. Car has never been run on fat, and car has never smoked. Not even the light haze I'm supposed to see at WOT, despite IQ setting. I have some smoke on startup now but thats it. Exhaust aimed at ground though, somaybe there's some and I just can't see it in the rear view? Turbo came from Bora Parts now Cascade German.

I'm planing to install a PD lift pump and a new fuel filter to be sure I am still seeing this behavior before I change anything with the turbo, but would like some more real world ALH data to be sure I should see the stated values from these tests. The car seeming like it has a flat spot below 2000 RPM has been a thing since 2019 when I first got it tuned. I have tried to figure it out multiple times without luck now, always told it is hardware related, but my hardware should be fine considering where it's coming from.

 

[burpod]

stop screw in my wifes car (old one fell out, threads had to be retapped for 6mm bolt, guess by me as to where it should be):

friend of mine vnt17 set screw (see original paint marks):

 

[adamss24]

I would count the threads, any more than 6 it’s too far. Ideally take it down and take it to a turbo shop to check, it’s not that difficult to remove…then you take the IF out of the Ecuation…

 

[pyromancer]

Pic of the threads is in the first post. Looks like 5 or 6 threads. Really trying to avoid pulling the turbo, I'm not even sure if there's a turbo shop around me I could take it to, or how to find one.

 

[burpod]

unless threads start stripping on you, there's no need to remove the turbo. it's also not that crazy-fine adjustment that a turbo shop needs to be involved with. clean, little wd40, then try to crack the nut (8mm socket iirc), try to free it up a little bit, then back out allen bolt a turn, and retighten. depending on conditions of threads, you might need to take the whole screw out and clean up all the threads and redo it. snap a pick from above and see where you're at... can almost guarantee this is one big problem with the low rpm lag, but i think there also other issues likely at play... both turbos i have shown pics of have been driven many miles, both tuned, nothing close to being dangerous as far as blowing up the turbo..

 

[PakProtector]

So you just did an injector install. Did you check the timing graph with the new injectors?
cheers,
Douglas

 

[Geobmx4life]

I’m wondering if a dawes device may apply to your situation

BoostValve Home Page - BoostValve Performance Turbo Controllers

Ric Gillis' Boostvalve turbo control valves. The original "G" valve MBC.

boostvalve.com

 

[pyromancer]

So you just did an injector install. Did you check the timing graph with the new injectors?
cheers,
Douglas

Yes, but Did not just install injectors...

 

[dhangejr]

Did you ever get to the bottom of this issue? I’ve been having the same issue for the last year.

 

[Nevada_TDI]

I put 18" of vacuum on the actuator, inserted a 0.030 feeler gauge and brought the stop screw up to the actuator arm.
It made a noticeable difference.

 

[pyromancer]

I did not find a great way to do this. From getting multiple pictures of others stop screws and getting a few people to measure I determined that ruffly 3ish threads showing was common. From the people I got to actually measure them most where at ruffly 3mm. I set mine to that and then in playing with going in or out from there 1/4 turn at a time what I determined was that it controlled how soon the turbo began to spool. If I remember correctly at 3mm I begin to spool at 1300rpm. Previously I wouldn't spool until 1900+ I don't recommend anyone mess with their stop screw unless something really seems wrong. Again I reset mine with some guess work because it really seemed off.

Trying to set your stop screw by vacuum seems flawed to me. So we are all on the same page as to nomenclature and what is being talked about, stop screw is the stop screw the lever arm on the turbo hits. It hits this and can't move further. Second pic above in burpods post it is the screw painted yellow. Normally no one should have to adjust this, it should be set correctly from the factory. Then we have the rod this goes to the vacuum can, on this is an adjustment nut that lengthens or shortens that rod. Adjusting the rod length with the adjustment nut affects what vacuum level you hit the stop screw, so unless you are positive your rod length is correct you can't use it to set the stop screw. If you need to adjust your rod length there are tons of posts about that. Nevada_TDI's post seems correct for doing that, I believe general rule of thumb is setting it between 18-20" of vacuum.

 

[dhangejr]

So , no more lag?
Got a fresh boost log by chance ?
I hate my car

 

[pyromancer]

My low end lag was taken care of. I did still have a spike, dip and recover in the boost logs but as said the turbo did start to spool lower. If you try this, again be very careful. I'm not recommending anyone mess with this, I have heard this can go wrong in that you can cause back pressure if you get the veins too closed, and/or you can lock the veins by getting them too closed going tip to tail and then they heat weld. I believe I just got a badly setup turbo and I didn't want to spend money on an exhaust pressure gauge so was willing to trial and error it...

As for logs unfortunately my laptops SSD drive gave up the ghost two days ago. Lost all my data. I can try to see if I can recover anything after new SSD shows up hopefully next week. I can tell you though that logs looked similar to what I posted an image above just with everything except the blue line shifted to the left. I believe I was meeting requested by 1900-2000rpms ish at WOT.