Turbo Clogged?

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.

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.

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.

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.

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!

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.