turbo trouble (after turbo cleaning and reinstall!)

Recently purchased a 99.5 MK4 jetta. I was told the VNT actuator was stuck and needed to be cleaned. I took the turbo off, cleaned the VNT rod and lever system, cleaned the vane assembly and machined backing plate (on the exhaust side), and reinstalled the whole package. Neither the VNT actuator nor the vanes moved before the cleaning. The ring a vanes moved freely when placed back on the exhaust manifold end of the turbo before the outboard end of the turbo was reinstalled, and once it was, the rod moved freely as well. Much to my dismay, i dont think the turbo is spooling up at all. I don't feel any added power at any rpms. I suppose its possible that the VNT actuator lever could have slipped out of the notch in the ring that controls the vane geometry during reassembly, but it felt like it mated fairly smoothly. I would think that even if the vanes did not move freely, the turbo would still kick in at some point?? any ideas on how to test if the vacuum chamber or vacuum lines are in working order, or what I should be checking? I saw that in some cases the MAF was a problem...afraid to say it, but I dont know what this does. also, when i examined the exhaust turbine, the lower edges of the blades appeared to be pretty significantly worn, and were no longer a straight edge. how concerned should i be??

thank you in advance for any information....or for just reading through the whole post!!!!

for the maf, unplug it and see if it runs better.

What codes are stored in the engine module?

see my sig for more information

If the ring slipped, it wouldn't go back together right. Or if you force it, you could bend the actuator lever.
The brass blades should be straight. Once you bolt the ring in, did you check each blade with a feeler gauge for clearance? Did you move the vanes by hand after you installed the ring?
Now that you have everything installed, you can use a vacuum pump like the mityvac and connect it to the diaphragm. Check if the actuator rod moves around 1/2 inch or more. I never checked the stroke of the diaphragm but it has quite a bit of travel.
If you apply vacuum and nothing moves, you might have to take the turbo apart again.

Also, (and oother more experienced people, feel free to correct me on this if I'm wrong) I believe if you're experiencing turbo trouble you should be getting alot of smoke while accelerating too.

Naimanator said:

Also, (and oother more experienced people, feel free to correct me on this if I'm wrong) I believe if you're experiencing turbo trouble you should be getting alot of smoke while accelerating too.

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I wouldn't count on that. I've been having turbo trouble (I think it was the N75 solenoid) but not a lot of smoke.

Butter, the MAF is the Mass AirFlow sensor. It is a common weak spot in our cars. To check if yours is bad, unplug the MAF's electrical connector and see if your car performs better.

The MAF is sticking into the middle of the big flex hose that comes out of your airbox. Just go follow the path that the air travels. It is the first sensor in the pathway once you leave the airbox.

If it's bad you'll have to buy a new one and install it, which is about a 5 minute job. Check tdiparts.com or another TDI vendor. Also, put some silicone dielectic grease (aka spark plug grease) on the electrical connectors when you put the new one in.

By the way I think it's hilarious that you pulled the turbo, disassembled and cleaned it as if it's nothing, but you don't know what a MAF is or where it is.

No offence, it's just funny because pulling the turbo and dissecting it scares the hell out of me, but I could change a MAF in my sleep.

BuffaloDiesel said:

By the way I think it's hilarious that you pulled the turbo, disassembled and cleaned it as if it's nothing, but you don't know what a MAF is or where it is.

No offence, it's just funny because pulling the turbo and dissecting it scares the hell out of me, but I could change a MAF in my sleep.

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I have to agree I thought that was weird........

BuffaloDiesel said:

By the way I think it's hilarious that you pulled the turbo, disassembled and cleaned it as if it's nothing, but you don't know what a MAF is or where it is.

No offence, it's just funny because pulling the turbo and dissecting it scares the hell out of me, but I could change a MAF in my sleep.

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haha! yeah i was pretty nervous to pull off the turbo. I only knew where the MAF was...and thats just from looking at a diagram on this site.

When i reinstalled the turbo, i could move the actuator ring fairly easily with my finger, which was something i could not do prior to the cleaning. I also could move the actuator rod up and down after the turbo was reinstalled. I should say, before the cleaning, there was a very noticeable difference around 2100 rmps, particularly in 3rd gear. Now I dont really notice it anywhere. I know the exhaust turbine is worn, but it seems that the turbo was spooling up before.

Also, I have a stage II In Motion chip, EGR delete, larger nozzles, port matched intake and exhaust and ARP studs...this all from the previous owner.

the worn edges are from the turbine hitting something, wonder how long the turbo will last... do you have a boost spike?

BAD NEWS!!!!!!!!!!
I was driving to work this morning, accelerating on an onramp onto the highway when WOOF I hear the sound of a lot of pressure being released. My acceleration drops off and I imediately hear the sound of the turbo spooling (it is very noticeable!). The car lagged considerably, and felt very limp/non-responsive. I pulled over to check to see if anything obvious hoses appeared to be disconnected, or any excessive oil leaks....but did not notice anything initially. When i started it back up it drove fine in low rpms. The turbo could be heard around 2000 rpm and the noise was very noticeable (a whurring noise of the turbine, not a grinding noise) but ZERO power from the turbo. The higher the rpm's the more black smoke. Some threads talk about white smoke being related to a blown turbo, but i dont notice any. The previous owner had a boost regulator valve (whatever its called) installed, so I'd be a little suprised if its an overboost issue....but i don't really know. I plan on looking to see if all the hoses are connected since that might explain the lack of powerful and loud turbo noise. Some threads speak of cleaning the N75.

so far its been a pretty unfortunate introduction to TDI's. Im holding out for a hopeful outcome...at least this forum is useful.

PLEASE HELP!!!!!!!!!!!!!!!!!!!

p.s. i will be out of town this week so wont be able to work on the car much....but i can still try and read up on everything so that im ready to roll when i get back.

Check yur boost hoses. If the two surfaces are not clean, dry and the clamp installed correctly in the proper groove.........POP. Off she comes.

Does your vacuum actuator hold vacuum? and vacuum getting to the actuator??

alphaseinor said:

the worn edges are from the turbine hitting something, wonder how long the turbo will last... do you have a boost spike?

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sorry...boost spike in the performance? or is that a component?! haha!! im still learning.

if in regards to performance, before i did the VNT clean i noticed a "spike" in the boost at about 2200 rpm. Before the most recent incident where i heard the loud noise, but after the turbo reinstall, i did not notice any boost. I do not have a boost gauge tho.

pghPAtdi said:

Check yur boost hoses. If the two surfaces are not clean, dry and the clamp installed correctly in the proper groove.........POP. Off she comes.

Does your vacuum actuator hold vacuum? and vacuum getting to the actuator??

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afraid i haven't gotten a chance to check the vacuum yet.

so does it sound more like a loose or cracked hose than a blown turbo? that seemed to be what I gathered from some previous turbo threads.

Check all your intercooler pipe connections. One of them must have come off. That's an easy problem to fix. You have to put the car on stands, take the bottom plastic shield off so you have access to the turbo and start from the compressor housing and look at all the connections closely. Sometimes the coupler just slips past the raised end of the pipe and it doesn't look like it's disconnected at all. Be thourough and don't assume that if it looks OK it really is.
Good luck

I had one of my intercooler hoses come loose once, sounds alot like what you're describing. I was fine driving it, but if I tried to accelerate too hard I could hear a large amount of pressurized air hissing out from the right front of the car.

yeah, i got a chance to look under the hood before heading out of town (in another vehicle) and the intercooler line is definately disconnected. Im pretty anxious to get back and continue the troubleshooting. im still a little perplexed that i didnt notice ANY performance boost after reinstalling the turbo...especially if there was enough pressure to blow the intercooler line off. possibly a back up in the intercooler or somewhere thereafter (although for some reason that seems unlikely)? I plan on testing the vacuum system, MAF and N75. Anyone know of a good thread to look at for N75 troubleshooting and/or cleaning?

Below is what I stole from another link:

You should be looking at the actuator arm of the turbo for movement - 1/2 in. at least. No movement would indicate either bad N75, or bad turbo actuator, or stuck VNT mechanism inside the turbo. Yes, the engine should be running. Another way to implement the test is to go to the engine section in VAG-COM, go to measuring blocks, go to channel 11, and then choose basic mode to start the test. The N75 should switch back and forth - about 10 sec on, 10 sec off. You should hear a 'clicking' of the N75 when it switches. To double check the N75 you can detach the vac hose going to the turbo actuator and in its place hook up a short piece of vac tubing to a vac gauge. If you don't have a vac gauge you can tape a very small plastic bag tightly to the vac hose. When the N75 kicks on/off the plastic bag will show the vac suction.

You might also find this ross-tech site helpful:

http://www.ross-tech.com/vag-com/tour/out_test.html


If you have a vag-com this works well. Good luck!

butter said:

yeah, i got a chance to look under the hood before heading out of town (in another vehicle) and the intercooler line is definately disconnected. Im pretty anxious to get back and continue the troubleshooting. im still a little perplexed that i didnt notice ANY performance boost after reinstalling the turbo...especially if there was enough pressure to blow the intercooler line off. possibly a back up in the intercooler or somewhere thereafter (although for some reason that seems unlikely)? I plan on testing the vacuum system, MAF and N75. Anyone know of a good thread to look at for N75 troubleshooting and/or cleaning?

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If the line isn't connected good, it can pop before you feel the boost. It's like a slight push on a swing, then nothing. Very slight push.

rdkern said:

If the line isn't connected good, it can pop before you feel the boost. It's like a slight push on a swing, then nothing. Very slight push.

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yeah that makes sense, but i drove the car for a day before this occured.

Take a look at EGR valve assembly and intake manifold for the usual clogging. If turbo is making pressure and there is a resriction in the IM, no gain as you describe. How many miles on the vehicle? Several mods on the car, do you have contact with previous owner? It could be tough to sort out. Is preformance just not what you expect or has it dropped off since you bought it?

jettawreck said:

Take a look at EGR valve assembly and intake manifold for the usual clogging. If turbo is making pressure and there is a resriction in the IM, no gain as you describe. How many miles on the vehicle? Several mods on the car, do you have contact with previous owner? It could be tough to sort out. Is preformance just not what you expect or has it dropped off since you bought it?

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Mods: EGR delete, larger nozzles, In Motion stage II chip, boost restricter valve, port matched exhaust and intake. Its got 97k on it, and i have contact with the previous owner.

performance has dropped off since i cleaned the VNT. Previously the vanes were frozen but still got a boost around 2200 rpm. Prior to the intercooler hose popping off (after reinstalling the turbo), I didnt sense any performance boost. Haven't gotten the chance to reconnect the hose or take her for a spin yet.

sorry to sound like a broken record! and thanks to all the ideas!! i'm pretty impressed by the TDI community

Alright, so I reconnected the intercooler hose. The previous owner tells me he recently put on a new N75. IWhen the car is turned on, the actuator rod travels approximately 1/2" downward, and when turned off the actuator returns to the original position.
I took the car out and let it warm up to normal operating temp. I ran through the gears smoothly and then pushed it a little more. I felt like the turbo MAY have been adding power, and felt a DEFINITE power boost at about 3500 rpm. Im not sure what kind of power curve I should expect.
How noticeble should the turbo be at say 1500-2500 rpm's? Is there a typical power curve graph anywhere that can help? What kind of psi should i look for at various rpms and how can i verify that I am getting those numbers (since I dont have a boost gauge)??

mods, once again: larger injector nozzles, In Motion stage II chip, EGR delete, ARP studs, Port Matched intake and exhaust manifolds. (i should add this to my profile)

oh and I have a boost limiter valve/overboost valve....whatever its called

I went ahead and bought an MAF sensor and thrust sensor since those came up as malfunctioning on the VAG-COM (thanks to a fella in Baltimore). After installing, i didnt really get the performance i was expecting (still dont really feel a pull from the turbo, and when i do its at like 3100 rpm), plus theres still more black smoke coming out than i would expect.

now what?!

Have you calibrated the boost valve? Too bad the VagCom isn't available now - since you could see what the MAF, MAP etc values are.

sorry, not really sure what you mean by calibrate the boost valve?
anywhere to find out how to do that?

Did I miss where you got out a vacuum pump and checked your vacuum system? Fr some reason, my check valve has a habit of going back together backwards and it causes the turbo to not work.

My thoughts on this is that the turbo hasn't been working right for some time which caused the vanes to become carboned up. Cleaning the turbo fixed the result, but it didn't fix the cause.

Get a vacuum pump and test the vacuum system.