VCDS tests concerning VNT and N75

[bc_bat]

When I run group 11 of the VCDS showing boost pressure the actual pressure does not follow the specified pressure closely. The actual pressure lags the specified pressure and the actual pressure is either 20% or so higher or lower. From reading other posts, I think these should match better.

If I perform a basic N75 test using the VCDs I do not see the VNT actuator move.
If I manually exercise the VNT actuator with the engine off, the VNT actuator moves smoothly and freely.
I think this means the N75 valve is malfunctioning.

Any thoughts on N75 being bad?

 

[Lensdude_com]

I would agree with you that replacing the N75 solenoid is the way forward

 

[P2B]

Problem could also be a vacuum leak.

Simon

 

[Lensdude_com]

The vacuum hose between the N75 and turbo actuator is usually the first hose to fail because of the extreme heat and length of the hose.

 

[bc_bat]

I disconnected that vacuum line at the N75 and connected the MityVac. The VNT actuator moved freely and the vacuum held meaning that vacuum line is good.

 

[Lensdude_com]

I think what fouls the N75 diaphragm is the material of the vacuum hose breaking down over time along with the many heating and shaking cycles.

 

[bc_bat]

It appears to me that the N75 can go full on or full off, but it can't cycle in between 0 and 100%. Does that sound like one of the N75 failure modes?

 

[P2B]

They usually jam up or go open circuit. How did you determine it can't cycle in between 0 and 100%?

Simon

 

[bc_bat]

When I graphed the pressure using VCDS the pressure could go high or low, but not in between. (The pressure is in between 0 and 100 when I rev the engine for short time periods which are not long enough for the pressure to increase to 100%. I would need to retest to verify this behavior.)
At low revs the specified pressure is around 1040 and the actual is 989. When the specified is around 1100 the actual is 1200+ or so (don't remember exactly).
I guess the sensor could be bad, but N75 is a popular failure.

2004, Jetta , BEW

 

[robnitro]

Do a 3rd gear wot run from 2k to 4k... post the log here.

 

[KERMA]

At low revs the specified pressure is around 1040 and the actual is 989. When the specified is around 1100 the actual is 1200+ or so

This is not a problem.

 

[bc_bat]

I have a graph, but when I copy and paste into the response nothing is pasted.??

 

[bc_bat]

Kerma, what should I see when I run the Basic cycle N75 test. I do not see the VNT actuator move.

 

[P2B]

The engine should be idling when you run the N75 test, and the actuator should cycle the turbo vanes between full boost and no boost positions.

If it's not moving, connect the mityvac to the N75 output and check if you have vacuum. If not, connect the mityvac to the N75 input to see if it's getting vacuum. If you have vacuum in but not out, the N75 is bad.

Simon

 

[KERMA]

allow me to elaborate

when specified is 1040 and actual is 989, that is at no-load idle and the engine is drawing a slight vacuum on the intake tract. These are normal readings.

The deviation is not enough to trigger closed-loop corrections (200 mbar is typical before closed loop corrections are fully activated). In other words, the ecu doesn't care about actual being different from requested by 51 mbar,especially at such low-load and low-rpm conditions.

Likewise when the actual is 1200 and requested is 1100. You are still in open loop operation. ECU is not making any corrections. This particular operating region is simply not that critical to require extremely fine tolerances. Any concern at this point, without further info, is nothing more than excessive worrying about nothing.

In order to properly diagnose the actuator (and turbo operation in general) you need VCDS and a buddy in the seat next to you, and a nice abandoned stretch of road. Floor it at approx 1500 rpm and hold full throttle until about 4000 rpm. 3rd gear should be fine.

Log this using VCDS measuring blocks group 11 and include group 1 as a concurrent reference to relative power. This will tell you the health of your actuator and turbo system as a whole.

The Group 11 basic settings exercise is simply a way to reset the baseline offset in the diagnostics. This can be useful if you have a new turbo or reflashed the ecu, but it doesn't really tell you much useful info in the way you seem to want it to.

 

[BobnOH]

To upload your graph use the same procedure shown in the upload pictures link in my signature. You'll can then paste the link to the uploaded file in this thread.
But start with the simple tests from post#14, or you can check down at the actuator. It should move all the way open when you start the car.

 

[robnitro]

Forget the graph, post the data... sometimes graphs are hard to read, since n75% is 0-100 and the rest are in the thousands, the scale is all wonky.

allow me to elaborate

when specified is 1040 and actual is 989, that is at no-load idle and the engine is drawing a slight vacuum on the intake tract. These are normal readings.

The deviation is not enough to trigger closed-loop corrections (200 mbar is typical before closed loop corrections are fully activated). In other words, the ecu doesn't care about actual being different from requested by 51 mbar,especially at such low-load and low-rpm conditions.

I can attest to that. I have up to 10 set to request 800-900 mbar.. and still n75 sticks to 27% and gives 1040 at idle. N75 map is set to 30% at that rpm/IQ too, so I think the ecu does it to make quiet idle (vanes quiet the exhaust).

 

[bc_bat]

Thanks for the information. I plan on making the before N75 and after N75 vacuum measurements with a pressure gauge while the N75 cycle test is running.
Here is the graph I recorded a few days ago. I will get around to making more measurements later.

 

[robnitro]

Test has to be done in gear, with power... idle/low power doesn't show anything conclusive or usable, and please please post the data.. like a screenshot of the excel (or if you dont have excel, a screenshot or paste the csv data.

 

[bc_bat]

I repeated the N75 cycle test and the VNT cycled as it should.

I recorded some road data and the results looked similar to below. It is an Excel graph so I hope it is readable without the tabular data. The boost looks like it is working with some lag.

I get the P101 error when I decelerate when it is cold (not summer). I found a trouble shooting guide that says to record block data 93 during decell. When decell occurs 100 is posted in channel 1, channel 2 should be between 1.05 and 0.95. For my car it is below 0.95 (0.8 - 0.9) which supposedly indicates:
1) a pressure leak between the turbo and cylinder head or
2) EGR stuck open or
3) MAF out of tolerance or
4) Charge Air Pressure sensor G31 problem or
5) Intake Air Sensor G72 problem or
6) Cam Timing issue

I did not see any leaks, but I did not do a smoke test; the EGR vacuum is good, I did not check the valve. G72 looked reasonable during the road test and the Torsion value is 0.0 or 0.5.
Is G31 sending the boost measurements? I need to check the MAF data, what should I see?

 

[robnitro]

Graphs don't help, and there is no n75 duty cycle on that graph.


Please post the actual numbers. Me like numbers they are crunchy and tasty

 

[robnitro]

Sorry I forgot to address your diagnosis steps:


I get the P101 error when I decelerate when it is cold (not summer). I found a trouble shooting guide that says to record block data 93 during decell. When decell occurs 100 is posted in channel 1, channel 2 should be between 1.05 and 0.95. For my car it is below 0.95 (0.8 - 0.9) which supposedly indicates:
1) a pressure leak between the turbo and cylinder head (FOR THIS LOG GROUP 03 and 11 at the same time- take maf/(map/1000)... if its much above 500 under boost, yeah you have a leak) but do this at a high load yesy
2) EGR stuck open or (you would have low maf readings instead in above test , less than 400per BAR)
3) MAF out of tolerance or (same test)
4) Charge Air Pressure sensor G31 problem or (above test would help)
5) Intake Air Sensor G72 problem or (check group 07 3rd number at idle, it should be 5-20 above ambient if idling- ex, 32f, 0 C, you would get 20 probably)
added, fuel temp, first number of group 07 should be no more than 80C- if just idling warmed up no hard driving, it should be a bit above ambient, like 40 or so)

6) Cam Timing issue (you said thats ok)

 

[bc_bat]

The graph below are various temperature readings for my car. Looks ok to me. The ambient reading and intake readings are the same and are in group 62. Group 62 repeats the Group 7 Intake Air Temp reading.

The injector readings are next for me to do although I remember they were all between -1 and +1.
This car has 187,000 miles. I replaced the cam with a Kerma Colt Cams Stage 1 PD Billet Camshaft at about 137,000.

O2 sensor replaced at 160,000; fuel filter changed every 20,000.

I would like to solve the P101 code and an inexplicable sudden 20% drop in mpg.

The odd reading I see with VCDS is group 73, Channel 3 Lambda/Oxygen is 3.6 which is supposedly too high and group 73, channel 2, Temp before Turbo always seems to be 246C and I don't know if 246C is normal.

 

[bc_bat]

I read an interesting article today which might explain my P101 issue. In my car, if P101 gets set it is always after deceleration from greater than 60MPH. The article I read said that many cars perform an EGR test when deceleration is detected. If the speed and temperature are in a specified range and deceleration occurs the EGR is cycled. Based on readings from the temperature sensor and MAP sensor the MAF sensor should read in a certain range indicating the EGR is working.
I am speculating one of those readings in my car is incorrect and the MAF sensor does not report as expected. This could explain why my P101 issue was not resolved when I replaced the MAF sensor.
I will run the test RobNitro suggested and hopefully it will point me in the right direction.
I usually have a little oil around the bottom of the intercooler, maybe the MAP sensor which mounts on top of the intercooler is being fouled by oil.

 

[bc_bat]

Injector data from Group 13 looks good IMO. At idle the deviation is well within +-1.0. The deviation goes above 1.0 while I am driving. Injector data axis is on the left, engine speed is the right axis.

 

[bc_bat]

Below is a graph of MAP, MAF, Boost and MAF/(MAP/1000). They all look good to me. The RPM is not as high as suggested, but apparently the RPMs are high enough to see actual boost and specified boost match. The MAF/(MAP/1000) is around 500 (red trace)which I think is good.
The top blue line is engine RPMs using the right axis. The MAF sensor is the orange trace and its range is ~200 to 1200. The middle two green and blue traces are specified boost and actual boost.
The EGR data (not graphed ) also looks like it is moving. I will check the pipe connecting exhaust to EGR to see if is clogged and causing the P101 code and again check for air leaks, although air leaks I have had on other cars typically cause the idle RPMs to increase. The engine idles at 903 RPM; I am not sure if that is high.

 

[robnitro]

You won't get an idle increase with an air leak on a diesel.
Before you take apart the egr try this:
group 03 is egr.
request is what egr wants to see
actual is what you are getting
last one- egr duty cycle is in % of how open the egr is...
example: my car at cold idle without egr is 490 mg/s actual.
with my egr on normally it asks for 260 mg/s , gets that at 75% egr cycle.

You can do group 03 then click basic settings to see it cycle... it should go down low, to like 200 or so and then up to 470-500 when egr off.

Those graphs are hard to distinguish... take a screenshot of a data plot if you want me to check it out or just upload the xls excel file to the pics tdiclub site, and link it here, we can download it and check it.

 

[bc_bat]

I uploaded the Excel file.

It is Group 3 data I had, the self test is not included, but you can see the EGR respond as I drive and it looks good. The only odd thing I see is sometimes the requested EGR maximizes at 1000 and the actual EGR is 1200.

I speculate the car is failing the EGR test during deceleration as described above causing P101 to trip. I thought maybe the exhaust tube is clogged and when the EGR cycles the EGR moves, but no exhaust recirculates.
How does the engine controller know the amount of EGR flow? If the controller calculates how much exhaust should flow based on the position of the EGR valve, the MAP sensor and temperature, it really doesn't know unless it senses a flow change in another sensor like the MAF or MAP. This would explain the P101 failure. The controller is expecting a change in the MAF based on calculations, but nothing changes due to a clogged pipe.
I am going to try and capture MAF data during a deceleration.

Also, taking off the EGR on a BEW is pretty simple, 3 Allen head screws and it comes out.

 

[BobnOH]

I have a graph, but when I copy and paste into the response nothing is pasted.??

You can upload it to the forum like a picture (see link in my signature)
Then paste a link to this thread.

 

[Lensdude_com]

I uploaded the Excel file.

It is Group 3 data I had, the self test is not included, but you can see the EGR respond as I drive and it looks good. The only odd thing I see is sometimes the requested EGR maximizes at 1000 and the actual EGR is 1200.

I speculate the car is failing the EGR test during deceleration as described above causing P101 to trip. I thought maybe the exhaust tube is clogged and when the EGR cycles the EGR moves, but no exhaust recirculates.
How does the engine controller know the amount of EGR flow? If the controller calculates how much exhaust should flow based on the position of the EGR valve, the MAP sensor and temperature, it really doesn't know unless it senses a flow change in another sensor like the MAF or MAP. This would explain the P101 failure. The controller is expecting a change in the MAF based on calculations, but nothing changes due to a clogged pipe.
I am going to try and capture MAF data during a deceleration.

Also, taking off the EGR on a BEW is pretty simple, 3 Allen head screws and it comes out.

Have you checked for stripped intake flap gears? The crud that can build up will jam the flap and bust a few teeth off the driven gear.
Skip ahead to the 2 minute mark in this youtube video to see what I'm referring to