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Turbo Clogged?

11773 Views 26 Replies 9 Participants Last post by  KarlC
2000 Golf with 1.9 ALH, 130,000 miles.

I cannot get any power above 2300 rpm. It behaves nothing like it did when new.
It behaves as though there is a waste-gate that dumps the boost. There are no fault codes stored.

The car cannot go above 75 mph, and struggles to maintain a set speed with the cruise control on. It behaves as though it can’t breathe. At some speeds, the car seems to surge and buck. Most often, it surges between 62 and 65 mph.

It is also very difficult to rev the engine above 3000 rpm when out of gear.

I cleaned the intake manifold this summer. It was down to less than 1â€￾ diameter. Upon reinstallation, the engine behaved much better for a couple of months. I was advised to check the air intake connections from intercooler/manifold to the air-box. All seems fine.

I changed the MAP sensor, without much improvement. The VCDS values seem to go above 500, so I presume it is working ok.

I also changed the EGR values, and that did improve the power dramatically.

I have also attempted a check of the VNT vanes without disconnecting the vacuum line or the rod connected to the mechanism. I had the car up on lifts and pumped the brake pedal to bleed off the system vacuum. The VNT vane control would not budge.

I suspect that the VNT is clogged and cannot move, driving the controller into limp-home mode almost permanently.

Is it possible that there is a vacuum leak? I can’t hear any hissing sounds per the video clip on the website.
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ALH engine the MAF should go up to around 850. 500 would be a bad sensor. Test the VNT vane control with this article: http://www.myturbodiesel.com/1000q_how_to/a4/VNTadjust.htm you really do have to use a vac pump to test it.

I've had boost hoses blow off and it sounds like it could be a boost leak. The stuttering at a certain rpm, smoke, and the feeling that the boost is dumping all suggest a boost leak. Do more testing. If the intake system won't hold light air pressure than you definitely have a boost leak. If you pressurize it and it immediately leaks off then look for a crack or small leak.
It's possible that when you removed the intake, one of the EGR bolts is loose. Check those too. You probably won't any hissing sounds over the sound of the engine.
I will check the EGR bolts this weekend. If there is a leak, would there be some soot around the joint?

I just figure that since the intake was so dirty (I was rather proud of the junk I was able to get out of it), that the turbo vanes would be affected too.

Thanks for the suggestion!
There might be a little soot but I would check the vacuum lines and solenoid operation first.
23-Mar-10 Update:
- I removed the belly pan and engine cover to look for obvious problems with hose connections. I could not find any loose joints in the air handling system.
- I used a mirror and light to look over the intake manifold and EGR joints. Again, nothing obvious.
- I tried to move the VNT actuator rod, and it will not budge.
- I don't have an air compressor or a vacuum pump to perform a pressure check or actuator test.
- I do have a VAG COM tool (and I'm not afraid to use it!) if there is any data to be logged or evaluated there. I have some screen dumps I can e-mail to someone if they would like to look them over.

Sorry to be so limited in what I can do. Should I consider taking the car to a dealership and having them run some of these tests?
It sounds like it might be the actuator. You can buy a vacuum hand pump for about $20 from places like harbor freight to test the VNT can. The dealer will charge you at least 1 hour which is normally $95/hour. Parts like OEM vacuum lines are about 5 times as expensive as a generic vacuum line. How much is your time worth?

Log MAP requested vs. MAP actual (this measures the boost in the intake system). Go for some drives and smoothly move the pedal back and forth. The lines should be close with minimal spikes. If you stomp on the accelerator and hold it, there should be a spike which levels out. Also log MAF actual vs. MAF requested as detailed in here: http://www.myturbodiesel.com/1000q_how_to/a4/maf.htm
Turbo Clogged? 25-Mar-10 Update

I decided to spend more time with the MAF sensor over the last couple of days.

MAF #1 (believed to have less than 2000 miles on it) was monitored, and will not generate a higher reading than 450 mg/H when I log data.

MAF #2 (believed to have around 40k miles on it) was changed out and improved driveability a little. I didn't make any measurements.

Next, I disconnected the MAF entirely, and the value is set to 550 mg/H.

Without an MAF, it drives a lot better. It smokes a lot and doesn't accel like it should. It still surges around 65 mph now and tops out at about 75 mph. I seem to be able to get power out of it up to 2600 rpm now, although the smoke is embarassing. Although I can't go really fast, people don't tailgate me!

Do I have two bad MAF's?

With the MAF values, I wonder if a downstream restriction - turbo clog - could restrict the ability of the turbo to exhaust enough to drive the compressor side. Perhaps the MAF values are real?

I have made several screen captures and pasted them into a MSWord file if looking at them would be helpful. Basically the MAF response has a very weak relationship to the theoretical value under any condition except idle.
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It's possible that you 2 bad MAFs. Some cars have gone through a few; I don't know why. It could be traced down to a bad air box seal letting dirt by the filter, a bad EGR, bad wire harness or plug, bad ECU.

The reason the EGR could be bad is that if it sticks open, the EGR gasses will "displace" air that would otherwise go by the MAF sensor. I've disconnected a MAF that was a little bad and the car ran worse. Because your car runs better without the MAF I suspect that is the problem. A downstream restriction could be causing this problem too.

Before buying new parts or spending more time testing stuff, test the vacuum line to the VNT and the VNT with a cheap vacuum pump. Test everything before buying new parts or else you're throwing money at it.

Please post the pictures. It's a bad idea to download a MSword or excel file from the internet and I don't think the forum lets you attach them to a post.
Turbo Clogged? VCDS image

I hope these are somewhat helpful - the filesize limits make it difficult to show the curves very well.

The first image shows theoretical MAF values required (green) and a fixed line (yellow) showing the MAF disconnected. Throttle values are in dark blue - hard to see without 400% enlargement.

The second image shows the MAF connected - theoretical is green, actual is yellow. Of some interest is the throttle value (100%). Peak values of MAF did not rise above 500, and lag the theoretical pretty dramatically.

Regarding the EGR, when I cleaned the intake, I believe it was working. There was a nice polished area on the shaft, about 6-8 mm long or so.

For the vacuum test, I'll get a tester. The H-F part went from $20 to $30 in two days! I have found it exceedingly difficult to remove these lines, so am thinking to cut them off and replace with new hose.


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Turbo Clogged? 10-Apr-10 Update

I'm back on this again. It's taken a while to get the 3.5 mm vacuum hose for the car, and I bought a hand vacuum pump to continue the diagnosis.

Following the VNT actuator check instructions, at key-on, the actuator does not move at all.

With the engine running - idle to 2000 rpm, the actuator is able to move about 3 mm and stops. The procedure suggests 10 mm of travel if all is well.

I went through the output tests with the VCDS tool, and unfortunately the fuel shutoff test just precedes the N75 output check. I can't click through the menu fast enough to keep the engine running. Suggestions are welcome.

I am a bit stymied with the vacuum pump, a Mityvac MV8000. I’ve not used this sort of tool before and can’t figure out what combination of pieces will allow me to evaluate the VNT actuator. It’s intended for automotive diagnosis and brake bleeding. The tool won't adapt to the hose.

Are there any suggestions on removing the vacuum hose? I’m planning to use an xacto knife to carefully cut the hose from the plastic nipple. At the N75, there is an extra sleeve over the hose/nipple junction that I hope doesn’t matter.

I want to understand the way the engine controls the VNT feature of the turbo. It seems to me that its job is to choke the exhaust at and off idle to spool up the exhaust turbine sooner. I am thinking that perhaps the event is binary, so the vacuum relay is on/off between idle and 1500 rpm or so. Is it possible that the N75 relay is operated with a PWM output to make more of a transition from off and on?

I keep coming back to the engine not getting enough air. The soot seems evidence of an overly rich fuel/air mixture. The car is so slow that I can barely keep up with a loaded semi-truck going uphill in a climbing lane.

Thanks for any of your thoughts.
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Start the engine again after it shuts off.

No movement = stuck turbo. If the turbo rod is adjusted all the way to the end of travel it won't move further but this isn't likely unless you or someone else adjusted it. Does it have a cone tip that you can press against the vacuum line? The vanes move smoothly and not on/off. The solenoid itself is on/off but it cycles back and forth so that the effect on the turbo is smooth.
Turbo Clogged - update 11-Apr-10

The VNT actuator moves after cycling through the other output tests. At engine shutoff, it moves away from the vacuum side of the actuator, approximately 5 mm. On engine restart, it moves back to the set-screw stop position.

We then operated the engine from idle to 2000 rpm. The actuator moved about half as far as during the N75 test.

For what it's worth, the other output tests cycle the EGR, and I can tell from the tone it functions. I took off the hose leading into the EGR to take a look and there is a polished shaft and some soot buildup.

Also, I've never adjusted the VNT actuator or the linkage.

I went to a hardware store, and they helped sort out how to use the vacuum pump if that's needed. A 2-inch piece of clear hose is all it took. I can work the tool now if needed.
vnt actuator

if you can't move the vnt actuator physically the recommended amount, I would disconnect the actuator from the vnt lever and see which is not moving.. either the vanes inside the turbo are sticking(which your local turbo shop should be able to clean up), or the actuator has filled up with debris/rust which will require replacement
Turbo Clogged - 17-May-10 Update

After another long break, I have some modest results to share.

A friend loaned me an air compressor, and with the help of a large vitamin bottle shoved and taped to seal, I applied 5-10 psi air into the intake hose behind the MAF. I also had to plug the breather plug going into the valve cover to pressurize the system. The oil filler cap was removed to ensure no pressure present in the crankcase.

After several tries and lots of duct tape, I don't hear any leaks in the air handling system. No noise anywhere. It seems to hold pressure - if what I'm doing is valid.

My next task is to excercise a vacuum pump on the VNT actuator.

For the vacuum relay, N75, can I check it by using a vacuum gage and with the engine running? My idea was to cut the hose going to the VNT actuator, apply vacuum to check the actuator at one end, and then check performance of the relay with the other end of the hose.

Thanks for your coaching - I'm still smokin' in a bad way.
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Clogged turbo????

Hi,just browsing thru this forum and came across your symptoms,actions,worries etc and thought you were reading my mind.I have 2000 golf alh engine with 126k miles acting EXACTLY like yours for 2 months getting gradually worse.Renewed MAF,brake switch,cleaned EGR,Turbo vanes,Eventually borrowed a friends vag com and got a code relating to injector needle lift sensor problem and found 2 very thin broken wires coming from injector No3 going into a plug then into the loom just behind black ball thingy.
Apparently injector 3 has a sensor on top which controls/monitors fuel and sends signal to pump.With these wires broken ,the pump can overfuel the system hence clogging the turbo,egr,cat etc with carbon/soot/unburnt fuel ,make the engine run like s**t and produce a batman like smoke screen from time to time.I spent last 6 weekends stripping ,cleaning,checking,rebuilding for nothing(apart from a broken wire)
Please check your wiring,could save you a lot of sleepless nights dude!
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Turbo Clogged? 18-Jun-10 Update

Thank you for the suggestion. I've been limping (and black-clouding) along since my last post, as I have had to take all spare time (and the entire garage) to help with a son's eagle scout project. Your discovery is very interesting. My only hitch with your theory is that I haven't had any codes at all. I'll give it a look though - diagnostics often gets you close to the real issue. I still believe there is something really wrong out there. I'm about ready to tear into the turbo just to rule it out. I understand that I need to confirm the vacuum lines are ok and that the VNT actuator is moving with a vacuum tool.
Clogged turbo?

Hi again,think you said in your first post that the actuator was moving 10mm up and down,well thats all mine moves after i had it off and freed it by soaking the whole thing in WD40 because i could not split the turbo.I can move the actuator by sucking the hose from up top.try that before removing turbo because its an ass of a job to remove.
Turbo Clogged? 19-Jun Update

Well, I checked the wiring on injector #3. All appears fine - nothing out of place that I can tell. Thanks for the feedback on the actuator movement. The engine diagnostics we ran a while back suggested to me that at least the VNT was working ok. Perhaps the turbo is not clogged or chokes downstream? What drives me nuts with this is that I take care of the car (bought it new in May 2000), and try to be thoughtful about what I do and how I drive it. I remind myself that the car is at an age where I am a student and the car is my teacher. There is so much to learn, and this site is a fantastic resource. Chitty, thanks a ton!
Turbo Clogged? 27-Jul-10 Update

Two updates to share - MAF sensors and vacuum pump work with the VNT.

I was able to borrow a new MAF sensor on the theory that I have two bad ones. Performance was about the same, so the new sensor was sent back home. This discovery was disappointing. On the other hand, I likely have two good MAF sensors.

Last evening, I cut the vacuum line from the N75 relay to the VNT actuator. Using a MityVac vacuum tool, I excercised the actuator. The actuator would not budge until I hit 15 psi (later down to 13 psi), and then with an audible "pop", the lever would move. I could get what I believe to be full movement between 23-25 psi.

I repeated the vacuum draw-down procedure about 20 times, hoping that the movement of the lever would drop below 13 psi. I could not see any further improvement and decided to hang it up for the night.

I then replaced the vacuum line, and took it out for a drive this morning. It feels better, with better power and less smoke. Perhaps I'm getting closer? Driving isn't quite as scary as it's been.

For the experienced folks, should I see a smooth linear movement of the VNT lever as you pull vacuum (similar to the video clip)? My impression is that it is sticking until the vacuum overpowers the friction. Perhaps I've loosened it up somewhat to get it to work more of the time.

Next, is it time to take the turbo off and clean it thoroughly?

In the meantime, I'll continue to replace the vacuum lines. I need some larger diameter hose - 3.5 dia isn't the only size that needs to be changed.

I really, really appreciate this site and the excellent coaching. I am learning, ever so slowly.
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