B6 Passat 3c 2007 125Kw 2.0 TDi. Intermittent black smoke, violent erratic revs

Hi all. I appreciate the help in advance.

Videos I managed to capture. They miss the first 10 seconds or so and you cannot see the exhaust smoke.
https://photos.app.goo.gl/AKFCHDv1NBaNhKED7
https://photos.app.goo.gl/viYmsUoFyYjcYaRRA
Symptoms: black smoke, no power, violent erratic revs. Lasts for about 5-20 seconds. No CEL. no fault codes when scanned with VCDS. Happens at any speed and also when engine is hot or cold. Engine is completely unusable when it happens.
This only happens once every week or so but seems to be getting more frequent. Putting it in sport mode doesn't resolve the issue. Only happens once per drive then resolves.
Plenty of power and the car drives great when it isn't having this issue.
I am no master with the VCDS but I cannot see any issues. Are there any meassuring blocks I should look at? The injector wear values were less than 0.5 difference.
I have replaced Diesel filter, air filter, tandem pump (previously had a small leak) .
My local mechanic and a Diesel and Turbo specialist had no idea.
My hunch is a sensor is giving intermittent bad signals and putting in too much Diesel or not enough air.
Let me know what I should try to diagnose this issue. I can do any scans needed with the VCDS.
Thanks everyone.

I have cleaned the egr and anti stutter valve. Any other ideas on what it could be or tests I should run with the VCDS.

I really have no idea what could be going wrong. Everything seems normal. Could it be the anti stutter flap activating when it shouldn't be. Any other ideas

If you suspect a falty sensor, start by checking/logging (using VCDS) the Coolant Temp Sensor G62 readings.
Another thing I would do is to check if your in-tank electric pump is working. Remove the upper hose from tandem pump and activate Output Test for the pump using VCDS. Spills fuel?

Henrick said:

If you suspect a falty sensor, start by checking/logging (using VCDS) the Coolant Temp Sensor G62 readings.
Another thing I would do is to check if your in-tank electric pump is working. Remove the upper hose from tandem pump and activate Output Test for the pump using VCDS. Spills fuel?

Click to expand...

Thanks for getting back to me Henrick. G62 looks fine. steady around 88 Celsius when running. I will check the fuel line at the tandem pump this weekend.

The car seems to now have a permanent issue. It runs 100% fine up to about 2200 RPM which it stays under in normal driving (Accelerates quickly, smooth gear changes). If I floor it and try get it to go above 2200 it just increases revs very slowly up to about 3000RPM then I get the glow plug light flashing and it wont rev any higher. It is like the turbo just stops at 2200.

I get the fault at the end of this post. I am thinking I need to check the vacuum like this guy https://youtu.be/Nl66nCaOlI0 (who it also looks like you helped). Also the fuel pump could be the issue.


000665 - Boost Pressure Regulation
P0299 - 006 - Control Range Not Reached
Freeze Frame:
Fault Status: 11000001
Fault Priority: 5
Fault Frequency: 3
Reset counter: 40
Mileage: 169220 km
Time Indication: 0
Date: 2019.09.26
Time: 10:13:48

Freeze Frame:
RPM: 3008 /min
Torque: 272.0 Nm
Speed: 42.0 km/h
99.45 %
Voltage: 13.90 V
Pressure: 2492.1 mbar
Pressure: 1640.1 mbar


Readiness: N/A

Henrick said:

If you suspect a falty sensor, start by checking/logging (using VCDS) the Coolant Temp Sensor G62 readings.
Another thing I would do is to check if your in-tank electric pump is working. Remove the upper hose from tandem pump and activate Output Test for the pump using VCDS. Spills fuel?

Click to expand...

Tested the in tank fuel pump. When activated with VCDS diesel comes out. There is not anything obviously wrong when flicking through VCDS apart from the new P0299 error and absolutely no acceleration when the car hits about 2200rpm. It seems that flooring it and hitting the kick down switch causes the issue instantly.

I went through and tested the vacuum on the turbo actuator and n75. All seems fine. The turbo actuator moves when I apply vacuum.

I have also reset all the factory defaults using VCDS. Could this somehow have caused this issue.

Can you think of any other tests to try? I cannot think what could be wrong. It is such a strange issue.

In EGR adaption mode i have Exhaust Gas Recirculation specified 1388.8 mg/str but an actual of 464.2 mg/str. does this indicate a faulty EGR valve?
When I run the EGR output test when the Lambda is at 50% the Mass Air Flow is around 280 mg/str. When the Lamda value switches to 0% Air flow is around 460 mg/str. Both at 50% duty cycle and 800 RPM.
I think I have 2 problems. the initial one from when I posted and the new one from when I cleaned the EGR valve and reset the default values. I wonder if I split a IC hose when I did the EGR. The supplied boost just drops away when the RPM reaches about 2200. I will jack it up and have a look.

I thought maybe the MAF. does anyone know what these should look like.
Gray: Maf actual
Red: Boost Actual

Red: Average mass airflow g/s
Yellow: Mass Airflow Calculated

Gray: Engine Speed
Blue: Boost pressure specified
Red: Boost pressure actual


A different time in VCDS: https://imgur.com/Mat1rTg
Red: MAF actual
Gray: Maf Calc
Green: Boost requested
Yellow: Boost actual

000665 - Boost Pressure Regulation
P0299 - 006 - Control Range Not Reached

^^^
This explains it all.
Stop looking at tandem pump and other things.
You have underboost condition.

I will not be able to tell what exactly is wrong with your car but this is what I would look at:
1) Turbo actuator. Does it hold vacuum? Easiest way to check it is to remove the pupe at N75 solenoid valve and use your mouth to create a vaccum there. You will feel if the vaccum is building inside the membrane. If the membrane is leaking, there won't be any vacuum
2) boost pipes. This will require car on lift, with engine underbody guard removed. Inspect all the pipes, all the joints. On pipes, look for cracks and oily residue. With age, they crack. Inspect all the joints to be tight and leak-free. It would be great if you could have a helper sitting inside, starting the engine and accelerating. Meanwhile you could use soapy water (or the emulsion which is used to detect tyre leaks) to spray on the intercooler plumbing joints to check for leaks.
Inspect the pipes from the top too
3) Use VCDS output test for boot regulation. the RPM will rise to about 1400, it will create and release boost periodically. Make sure that the "boost" and "no boost" pressure differs by ~180 mbar or so. It may have problems building the pressure due to sticky/faulty N75 valve

Hope this helps

Thanks for the suggestions Henrick.

1) I had previously tested the whole vacuum system. All seems fine. N75 turns on and off and turbo actuator moves freely and holds vacuum.
2) I have looked everywhere on the boost pipes. I cannot find a leak. It doesn't make sense to me that a boost leak would occur exactly when I replace the tandem pump and clean the egr and anti stutter.
3) I will try the boost regulation test today.

If it isn't a leak in the boost system what else could be causing low boost?

I have done a smoke test. A small split but that had been resolved and the problem still exists. Turbo actuator holds vacuum. Any idea what else could be causing low boost? It makes no sense to me.

Henrick said:

000665 - Boost Pressure Regulation
P0299 - 006 - Control Range Not Reached

^^^
This explains it all.
Stop looking at tandem pump and other things.
You have underboost condition.

I will not be able to tell what exactly is wrong with your car but this is what I would look at:
1) Turbo actuator. Does it hold vacuum? Easiest way to check it is to remove the pupe at N75 solenoid valve and use your mouth to create a vaccum there. You will feel if the vaccum is building inside the membrane. If the membrane is leaking, there won't be any vacuum
2) boost pipes. This will require car on lift, with engine underbody guard removed. Inspect all the pipes, all the joints. On pipes, look for cracks and oily residue. With age, they crack. Inspect all the joints to be tight and leak-free. It would be great if you could have a helper sitting inside, starting the engine and accelerating. Meanwhile you could use soapy water (or the emulsion which is used to detect tyre leaks) to spray on the intercooler plumbing joints to check for leaks.
Inspect the pipes from the top too
3) Use VCDS output test for boot regulation. the RPM will rise to about 1400, it will create and release boost periodically. Make sure that the "boost" and "no boost" pressure differs by ~180 mbar or so. It may have problems building the pressure due to sticky/faulty N75 valve

Hope this helps

Click to expand...

Great advice by Henrick!

I would look at the actuator. You can try the EASY zip tie fix, to see if that helps the condition any.

I am 90% sure you have a vacuum leak. I had a vacuum leak at the joint behind the tandem pump and the car was doing the exact same things your car is doing. Check all those little hoses, the hard ones tend to crack over time and leak.

I had tested all the vacuum hoses and could not find any leaks. The N75 was building pressure for the VNT as it should be. VNT was holding vacuum and appeared to move freely but I am not sure how far that should move. Is there any obvious limit in/out markings.

What is the zip tie fix?

mextdi said:

Great advice by Henrick!

I would look at the actuator. You can try the EASY zip tie fix, to see if that helps the condition any.

I am 90% sure you have a vacuum leak. I had a vacuum leak at the joint behind the tandem pump and the car was doing the exact same things your car is doing. Check all those little hoses, the hard ones tend to crack over time and leak.

Click to expand...

Make sure your vacuum numbers line up with the video during the N75 output test. In the video he has ~23inHg at the actuator cycling on and off during the output test. When I had this fault code I was only getting 18inHg at the actuator during the output test.

The car is with the mechanic still so I cannot test the vacuum again. It from memory it was right when I tested it. The mechanic thinks it could be the DPF. Could that be the case? Would that cause the boost to only work up to 2200RPM?

I have given up trying to fix it and just traded it in for a big loss. Its a shame as it was such a nice car.

I'm kinda disappointed none of the "gurus" chimed in to help/advise your problem.. ..sorry..I wish I could of helped...