Bad EGR valve?

Dr. Greenthumb

Veteran Member
Joined
Apr 1, 2011
Location
Denver
TDI
05' Passat GLS 95' Merc E300D
Having boost and airflow issues after new turbo install. I will bullet point what I have done and see if this rings any bells.


I replaced the turbo - used the garrett.
  • No adjustments needed, actuator arm hit stop at 20 in hg
  • Replaced all intake gaskets and exhaust gaskets.

No boost.
  • Request 900 mbar
  • Actual isn't much over atmospheric

Low airflow through the MAF.
  • No blockage in the intake path.
  • Per vag com, Requested is 800mg/str - actual is a bit over 400mg/str.
  • Replaced MAF sensor with new Pierburg sensor.
  • No change.

All vacuum lines replaced.

Vacuum solenoid tested faulty
Replaced with new solenoid

Throttle valve faulty and replaced ~5K miles ago

No CEL at any point.

So I am looking at the EGR valve now and here is my question, finally. It seems to be faulty.
When engine running
  • un-plugging harness does nothing -
  • re-connecting the motor smooths out for a second and returns to poor running
  • No CEL

Removed valve and cleaned soot and electrical

Connected to harness and ran output test
  • Valve did not move freely
  • Valve did not seat
  • Open/Close cycle inconsistent

The question is - does the valve sound faulty, or an electrical issue?
 
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oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Why did you replace the turbocharger?

The BHW has the simplest of any TDIs [sold here] for its vacuum system. So it is fairly easy to troubleshoot. Unlike all the rest of the VNT equipped TDIs, the BHW only uses vacuum for boost control. That's it.

Only downside is that the N75 valve is located in a bit of a goofy spot, but you can get the whole vacuum system up and out of the car in one chunk after you remove the air cleaner assembly and air inlet tube to the turbo. You'll need a shallow 8mm Allen bit, but you remove the two Allen bolts that hold the bracket for the vacuum reservoir in place and you slide the whole thing up and out.

Source vacuum from pump, at firewall.

One way (ying yang) valve, near air cleaner.

The vacuum vent line goes back up to air cleaner.

N75 is a simple duty cycle solenoid, that controls how much vacuum goes to the VNT actuator.

You can start the engine and do the Basic Settings boost control test and watch the VNT actuator moving up and down. If it does not move, you have a vacuum problem somewhere.

So long as the EGR is SHUT when it is supposed to be, it will have no effect on boost.
 

Uberhare

Veteran Member
Joined
Sep 3, 2006
Location
Ontario, Canada
TDI
Too many.
Is the request value 900 mbar or 900 mbar above atmospheric (980ish)? If the # displayed in vagcom is 900 then the ECU is not asking for boost.
 

Scubanero

Veteran Member
Joined
May 30, 2007
Location
Calgary AB
TDI
2005 Passat Wagon
It certainly sounds like the valve is faulty but may or may not be the only problem. I had to replace mine because the integral position sensor died. If I forced the valve closed and left it unplugged it ran well. If I plugged it in, it would never close after the start up calibration cycle.
 

Dr. Greenthumb

Veteran Member
Joined
Apr 1, 2011
Location
Denver
TDI
05' Passat GLS 95' Merc E300D
Is the request value 900 mbar or 900 mbar above atmospheric (980ish)? If the # displayed in vagcom is 900 then the ECU is not asking for boost.
It is asking for 900 mbar, atmospheric is reading 750 mbar. Pushing on the throttle, the requested get up into the 1100 mbar range and actual stays around 750 mbar. Actual and request never get close to each other. Same with airflow.
 
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Dr. Greenthumb

Veteran Member
Joined
Apr 1, 2011
Location
Denver
TDI
05' Passat GLS 95' Merc E300D
If you haven't done the basic settings group 11 charge pressure control test you need to do that first. It is the starting point for troubleshooting boost problems.

If it's setting MAF codes, is the cam good? Any weird "bupping" sound from the intake? Normal MAF readings at idle will be ~450mg/stroke.
Group 11 pressure control test = Group 11 measuring blocks? While in group 11 measuring blocks, I ran engine up 2000-2500 rpm. Request for boost goes way up, actual doesn't move much and never reaches requested. Same goes for air flow, request goes up, actual stays the same.

The cam was replaced about 30K ago with a cam from Kerma TDI. No bumping in intake.

I'll try and get graph posted asap.
 
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Dr. Greenthumb

Veteran Member
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Apr 1, 2011
Location
Denver
TDI
05' Passat GLS 95' Merc E300D
Why did you replace the turbocharger?
It ate itself up, completely fubar
The BHW has the simplest of any TDIs [sold here] for its vacuum system. So it is fairly easy to troubleshoot. Unlike all the rest of the VNT equipped TDIs, the BHW only uses vacuum for boost control. That's it.
Only downside is that the N75 valve is located in a bit of a goofy spot, but you can get the whole vacuum system up and out of the car in one chunk after you remove the air cleaner assembly and air inlet tube to the turbo. You'll need a shallow 8mm Allen bit, but you remove the two Allen bolts that hold the bracket for the vacuum reservoir in place and you slide the whole thing up and out.
Source vacuum from pump, at firewall.
One way (ying yang) valve, near air cleaner.
How can you tell if it's in the right direction? Which end - black or white - is on the vacuum pump side?
The vacuum vent line goes back up to air cleaner.
N75 is a simple duty cycle solenoid, that controls how much vacuum goes to the VNT actuator.
You can start the engine and do the Basic Settings boost control test and watch the VNT actuator moving up and down. If it does not move, you have a vacuum problem somewhere.
Moves like it's supposed to using the output test. When the test goes to 33%, the engine runs very rough. I have been confused about duty cycle. When I start the engine, the EGR duty cycle goes to 100% - actually a little over. Does that mean the valve is 100% open, or 100% closed?.
So long as the EGR is SHUT when it is supposed to be, it will have no effect on boost.
Does this sound like a vacuum issue? I tested the N75 valve and found low readings going to VNT actuator. All vacuum lines replaced. Vacuum reservoir replaced about a year ago.
 
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oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Black half of valve towards vacuum source (the pump).

It is difficult to say if you have a vacuum issue or not. If the vacuum system is not working, for whatever reason, and the VNT mechanism does not work, you should get a P0299 low boost deviation pretty quickly when you go drive the car.

The EGR valve, if it is working correctly, will duty cycle as requested. A simple check is to run the engine for a bit, enough to get some heat in it, and let it idle and watch the MAF actual vs. requested. They should match, and that means the EGR valve is working. After a few minutes of idle, the EGR will shut off, you will immediately see the actual MAF jump way up, maybe go from 250 to 450? Rev the engine, then the EGR will come back on and actual will once again match requested. That at least is a simple functional check of the MAF and EGR at least working at idle, which at least lets you know the wiring and controls are all working.

Did you install a new Garrett turbo? Was there a massive amount of oil pushed into the exhaust?
 

Dr. Greenthumb

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Location
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05' Passat GLS 95' Merc E300D
New Garrett turbo. Yes, lots of oil into exhaust. The cat was clogged, but now it is not :)

I checked vacuum to VNT actuator. It was ok.

Got things put back together and started it up. The boost requested and actual finally line up.

Mass air flow still off - request 800, actual 350. These never line up when engine is warm.

Checked readiness and EGR = Failed or incomplete.

Finally threw a fault code. 16791, EGR Potentiometer (G212) signal too low. I am going to check wiring and connector.
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
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Location
outside St Louis, MO
TDI
There are just too many to list....
OK, so it sounds like your EGR valve is bad.

I would open it up (a few Torx screws) and slide the plastic part up and off. Look for signs of soot and/or oil inside there. That can cause them to malfunction.
 

Dr. Greenthumb

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Location
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05' Passat GLS 95' Merc E300D
Tons of soot and oil in there. I cleaned it out the other day. Used a quick dry electronics cleaner for motor/potentiometer. Cleaned carbon and soot from valve mechanics. No change.

I picked up a new EGR valve and put it in this morning. Boost ok. MAF still off.

Just tested continuity. All wires made tested shine bright, except for one - it was very dim.

Warmed up motor again. Rev'ed it up and EGR stays at 100.6% duty cycle almost all the time, until I lift off the throttle. Within a second the duty cycle dips down and then goes back to 100.6%

MAF requested and actual never line up.

Lots of white smoke.
 

oilhammer

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Joined
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Location
outside St Louis, MO
TDI
There are just too many to list....
Hmmm... lots of white smoke? Not good.

Do you think it is leftover oil in exhaust system?

Or is it unburnt fuel (bad combustion)?

Is it possible the engine ingested some oil when the turbo failed?
 

Dr. Greenthumb

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Location
Denver
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05' Passat GLS 95' Merc E300D
Ok, not lots of white smoke. More like the amount you get on a cold morning.

I'm trying to find the group number in vag com for the EGR valve. Vag-wiki says group 74, but that's not it.

Wiggled some wires, now comprehensive components, fuel system, EGR recirculation failed. Sounds like a problem with a wiring harness.
 
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Uberhare

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Sep 3, 2006
Location
Ontario, Canada
TDI
Too many.
Denver right....Never actually worked on a TDI at that altitude. That will certainly change things! It's still only asking for 5 PSI. Certainly something wrong there.

It is asking for 900 mbar, atmospheric is reading 750 mbar. Pushing on the throttle, the requested get up into the 1100 mbar range and actual stays around 750 mbar. Actual and request never get close to each other. Same with airflow.
 

Uberhare

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Location
Ontario, Canada
TDI
Too many.
I had an S4 that ate the turbos take a week of driving to fully clear itself. Mind you we did find one of the impellers in the cat.

Hmmm... lots of white smoke? Not good.
Do you think it is leftover oil in exhaust system?
Or is it unburnt fuel (bad combustion)?
Is it possible the engine ingested some oil when the turbo failed?
 

oilhammer

Certified Volkswagen Nut & Vendor
Joined
Dec 11, 2001
Location
outside St Louis, MO
TDI
There are just too many to list....
Well I cannot say I have ever seen a BHW with a wiring problem BUT I have seen some harnesses start to chafe where it goes past the charge air tube and tandem pump near the firewall on its way to the intake throttle flap and EGR valve. May want to look closely in that region.
 

Dr. Greenthumb

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Location
Denver
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05' Passat GLS 95' Merc E300D
Denver right....Never actually worked on a TDI at that altitude. That will certainly change things! It's still only asking for 5 PSI. Certainly something wrong there.
Actually in Monument CO @ 6800ft. Where is the sensor for barometric pressure? The reading is wrong, it is using the pressure at sea level. The barometer reads 584mmHg today - car thinks it's at sea level.
 

Dr. Greenthumb

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Location
Denver
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05' Passat GLS 95' Merc E300D
584mmhg is about 768millibar, pretty close to what the ECU is reporting. I don't see the problem.

Actual and requested boost will never match if you're just revving the engine in neutral. A turbo needs heat, that means load and fuel to function. Drive it and watch the readings.
I think it is time to roll her down the road. Last time I did this I pissed all the neighbors off with a huge, stinky cloud of burnt motor oil.

Replacing the EGR got boost where it needs to be. Hopefully no smoke screen this time.
 
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