'96 Passat AAZ lacks turbo boost

[the_old_diver]

I had a replacement AAZ engine fitted a couple of weeks ago and have been driving very gently since then due to a very noisy wheel bearing. I replaced that yesterday and now find that I can't hear the turbo coming in. If it is working, then it is so subtle as to defy detection.

I was just looking under the bonnet and saw that the connecting rod on the turbo (wastegate actuating rod?) wasn't moving when I revved the engine. Making sure that I didn't alter the setting of the lock nuts, I slackened them back one at a time and I found that the lever going into the turbo would move back and forth but the actuating rod could not be manually moved in and out of the bit on the other end. In its "stuck" position, the lever going into the turbo is almost as far to the right (looking at the engine from the front) as it will go.

I also noticed that the shiny 1" dia pipe going into the stainless steel valve (EGR valve?) is getting barely warm.

I was wondering about leaking vacuum hoses but they are covered in cotton braid and difficult to examine.

Can anyone tell me "how much and when" that actuating rod should move, and what is the correct sequence of tests please?

Thanks for your time. OD

[the_old_diver]

More info - It seems that the vacuum is generated by a pump down near the oil filter and comes through a thin black pipe to port B on a little black device shown in the photo. A yellow pipe then leads away from port A to a tee-piece with one branch going into the EGR diaphragm(?) (stainless steel thing like a flying saucer) and the other branch going to the wastegate actuator(?). On the kitchen table, the resistance across the electrical contacts is 269 ohms and the inner vacuum nipple - the one with the braided pipe removed - is open to the port marked O. Edit - no it's not, it is open to the port on the end of the valve which had it's cover removed when I took the pic. The outer pipe with the braided hose still on is closed off whether sucking or blowing. Guessing that this is an electrically operated vacuum valve I applied 12v to the terminals and nothing happened - no ports opened or closed, no sound and no measurable current drawn. Edit#2 - on tickover the electrical connector to the valve has negligible volts coming through but above about 1500 rpm it jumps to 13.7V

Dear Marge, is this normal?

Oh yes, while I was at it I connected the black vacuum line from the vac pump straight into the tee piece to wastegate actuator and EGR, which immediately warmed up for the first time. I took the car for a trip along the street like this and power was even worse than before, with some grey smoke. Hope this helps someone to understand what is going on. OD

[the_old_diver]

Another update, dear readers.
The black plastic thing in the photo above doesn't seem to do anything. It seems to be between the vacuum pump and the wastegate actuator and EGR valve, which also don't seem to do anything. Seeing that the wastegate operating lever wasn't as far on one direction as it would go, I altered the locking nuts so it was at one end of it's travel. I now have turbo boost of sorts and can hear a distant Tawny owl under the bonnet. I doubt that the wastegate is opening, but then I rarely rev above 2500 so maybe this doesn't matter and overboost might not be my biggest problem.

Any contributions welcome, and I'll ask a simple Q about the thing in the pic in the General forum since no-one has drifted past here yet.
Cheers, OD

[erico]

Another update, dear readers.
The black plastic thing in the photo above doesn't seem to do anything. It seems to be between the vacuum pump and the wastegate actuator and EGR valve, which also don't seem to do anything. Seeing that the wastegate operating lever wasn't as far on one direction as it would go, I altered the locking nuts so it was at one end of it's travel. I now have turbo boost of sorts and can hear a distant Tawny owl under the bonnet. I doubt that the wastegate is opening, but then I rarely rev above 2500 so maybe this doesn't matter and overboost might not be my biggest problem.

Any contributions welcome, and I'll ask a simple Q about the thing in the pic in the General forum since no-one has drifted past here yet.
Cheers, OD

Hi,
The manual shows that device as the wastegate bypass regulator valve N75. here is the blurb from the Bentlet repair manual for checking the device. First ting you must do is disconnect the connector of the wastegate bypass regulator valve N75 from the harness connector and go through the following procedure.

• Start engine and briefly raise to maximum speed by operating throttle

Wastegate Bypass Regulator Valve -N75- operating rod -2- must move

• If operating rod does not move:

• Check Wastegate Bypass Regulator Valve -N75- lever -1- for ease of movement. If operating rod and lever are corroded together, replace turbocharger.

• If operating rod does not move, even though lever is free to move:

• Replace wastegate -3-.

Bummer that you readjusted the actuating rod length already. You bypassed a preset for the check when you did that.

FYI Here is how to return the position of the rod back to specifications.

Adjust rod length -3- so rod eye will install easily on lever pin -5- (lever lies against stop with no play).
Shorten operating rod 8 full turns from this position.
Tighten lock nut -1-.



edit: BTW is your turbocharger a KKK or Garret model? There was a recall program to replace the KKK models as they had a big tendancy to die due to oil starvation on engine startup at high revs.
Regards,
Eric

[the_old_diver]

Eric- many many thanks for your post! Where you wrote "disconnect the connector of the wastegate bypass regulator valve N75 from the harness connector" does this mean to disconnect the electrical connector on the N75?
As far as I can see, (difficult, even with a mirror) there are two pipes going into the actuator - that is, the gold coloured cylindrical bit which makes the rod move. One comes from the N75 and the other comes from the body of the turbo through a thicker pipe with a banjo connector on one end. At present the pipe between N75 and actuator seems permanently open to atmosphere via the N75. If the thicker pipe is also a vacuum pipe which acts as an alternative vacuum source, could this vacuum simply bleed away through the open N75?
If you have the time to answer this I would be extremely grateful, but if not thank you very much for pointing me in the right direction to sort the problem.
Cheers, OD
Edit - yes it's a KKK, but would a recall still be valid on a 12 year old car?

PS If anyone out there has a spare Bentley Manual for sale, please PM me.

[erico]

Eric- many many thanks for your post! Where you wrote "disconnect the connector of the wastegate bypass regulator valve N75 from the harness connector" does this mean to disconnect the electrical connector on the N75?
As far as I can see, (difficult, even with a mirror) there are two pipes going into the actuator - that is, the gold coloured cylindrical bit which makes the rod move. One comes from the N75 and the other comes from the body of the turbo through a thicker pipe with a banjo connector on one end. At present the pipe between N75 and actuator seems permanently open to atmosphere via the N75. If the thicker pipe is also a vacuum pipe which acts as an alternative vacuum source, could this vacuum simply bleed away through the open N75?
If you have the time to answer this I would be extremely grateful, but if not thank you very much for pointing me in the right direction to sort the problem.
Cheers, OD
Edit - yes it's a KKK, but would a recall still be valid on a 12 year old car?

PS If anyone out there has a spare Bentley Manual for sale, please PM me.

1) Yes, disconnect the connector on the N75.

2) @ 12 years? Probably not, but cannot hurt to inquire. There is a group of cars affected here is the group that recall TK affected. Early production year vehicles.
WvW_ _ _3A_TE000001 - WvW_ _ _3A_TE130028

3) The N75 shouldn't be open to the atmosphere. It is an electrically controlled actuator that is sealed when the hose and banjo fitting is in place. Do you mean that you can see an open place on the diaphragm?

4)BTW...do you have a VAG-COM that you can connect to see if the OBD system shows any DTC code?

Have a read of this thread at the Bentley Technical discussion forum. It might have some good info for you. It is all about lack of turbo boost!



Regards,
Eric

[the_old_diver]

OK - I'm confused by the names of things. There are some excellent photos of a turbo like mine in this post - https://www.vwaudiforum.co.uk/forum/s...ad.php?t=19945.
The turbine side of the 'charger is rusty steel, the compressor side is aluminium, the actuating rod is clearly visible connecting the wastegate lever on the rusty bit with what I would call the "wastegate actuator" - the yellowish cylindrical bit with two pipes going into it. So far, so good and the N75 "wastegate bypass regulator valve" should be on the other end of the pipe going nowhere in the photos.

I've had a problem with my VAGCOM today - it couldn't find the engine modules, but it did find
Control Module Part Number: 028 906 124 A / Component and/or Version: Turbo-Diesel V01 / Software Coding: 00127 / Work Shop Code: WSC 00000 1 Fault Found:
01265 - Exhaust Gas Recirculation Valve (N18) - 31-00 - Open or Short to Ground

This is confusing me because the EGR valve itself has no electrical connections, and is pneumatically operated by the black solenoid valve in my photo above, which is also connected via a "tee-piece" to the wastegate actuator with the rod coming out of it. So the ECU cannot know what the wastegate actuator is doing, only what it has been signalled to do by the opening of a valve N18 / N75 in the vacuum circuit.

So is the N18 in my VAG-COM the same as other people's N75 - " Wastegate bypass regulator valve" ? Either I'm much thicker than I thought or someone can't write a precise manual, or both :-)

Think I'll go and stroke my cats.....

OD

PS Final thought re wastegate actuator - do both pipes go to the same side of the diaphragm? I can visualise that pipe coming from the compressor output via the banjo nut and feeding positive pressure under the diaphragm, pushing the rod into the actuator and opening the wastegate once a certain boost pressure is achieved...

[erico]

OK - I'm confused by the names of things. There are some excellent photos of a turbo like mine in this post - https://www.vwaudiforum.co.uk/forum/s...ad.php?t=19945.
The turbine side of the 'charger is rusty steel, the compressor side is aluminium, the actuating rod is clearly visible connecting the wastegate lever on the rusty bit with what I would call the "wastegate actuator" - the yellowish cylindrical bit with two pipes going into it. So far, so good and the N75 "wastegate bypass regulator valve" should be on the other end of the pipe going nowhere in the photos.

I've had a problem with my VAGCOM today - it couldn't find the engine modules, but it did find
Control Module Part Number: 028 906 124 A / Component and/or Version: Turbo-Diesel V01 / Software Coding: 00127 / Work Shop Code: WSC 00000 1 Fault Found:
01265 - Exhaust Gas Recirculation Valve (N18) - 31-00 - Open or Short to Ground

This is confusing me because the EGR valve itself has no electrical connections, and is pneumatically operated by the black solenoid valve in my photo above, which is also connected via a "tee-piece" to the wastegate actuator with the rod coming out of it. So the ECU cannot know what the wastegate actuator is doing, only what it has been signalled to do by the opening of a valve N18 / N75 in the vacuum circuit.

So is the N18 in my VAG-COM the same as other people's N75 - " Wastegate bypass regulator valve" ? Either I'm much thicker than I thought or someone can't write a precise manual, or both :-)

Think I'll go and stroke my cats.....

OD

PS Final thought re wastegate actuator - do both pipes go to the same side of the diaphragm? I can visualise that pipe coming from the compressor output via the banjo nut and feeding positive pressure under the diaphragm, pushing the rod into the actuator and opening the wastegate once a certain boost pressure is achieved...

Prior to were running the VAG-COM diagnostic test did you initially clear all the DTCs stored?

Did you have the wastegate regulator valve N75 connected?

The Bentley manual's schematics show both the EGR (Exhaust Gas Recirculation) Vacuum regulator solenoid and the wastegate regulator valve N75 as two seperate devices. The block diagram of the TDI Diesel Electronic control system also shows that, although they appear to be almost identical.

The EGR (Exhaust Gas Recirculation) Vacuum regulator solenoid connector wires are black/yellow and white. The wastegate regulator valve N75 connector wires are black/yellow and brown/blue. This is what the Bentley manual schematic shows for 1995, 1996 and 1997 TDI 1Z engines.

The manual is not as clearly written as it should be. The manual says that (even though one is described)...TDI engines do not have a wastegate. The turbine blades speed is controlled by vanes inside the turbine housing. That is what the Wastegate actuator controls.

Interesting

On your final thoughts... one hose provides negative pressure (upper side of wastegate )and the other hose(bottom side of diaphragm) provides atmospheric pressure. They are on opposite sides of the wastegate diaphragm. So it is the exact opposite to what you were visualizing.

The ECM actuates the Boost Pressure control valve (inside the turbocharger) via the wastegate regulator valve N75 to move the turbine's vanes to a more closed angle to increase boost(higher turbine speed) when the ECM detects increased engine speed.

When the ECM senses lower engine rpms and the vanes are moved to a more closed angle by the wastegate regulator valve N75, reducing exhaust gas pressure and turbine speed, but allowing more exhaust gases to flow and extracting less energy from the exhaust gases.

I just looked at the manuals DTC code chart. a bad EGR vacuum regulator solenoid valve N18 will cause reduced power output and black exhaust.


Regards

[the_old_diver]

Eric - again many thanks for your help. I cannot make the wastegate actuator move but I will get the turbo off my old engine in the next few days and try to fit that instead.
Prior to were running the VAG-COM diagnostic test did you initially clear all the DTCs stored? Yes.

Did you have the wastegate regulator valve N75 connected? Yes

The Bentley manual's schematics show both the EGR (Exhaust Gas Recirculation) Vacuum regulator solenoid and the wastegate regulator valve N75 as two seperate devices. The block diagram of the TDI Diesel Electronic control system also shows that, although they appear to be almost identical. Bit of confusion here Eric - mine is an AAZ, which isn't a TDI- see picture.

The EGR (Exhaust Gas Recirculation) Vacuum regulator solenoid connector wires are black/yellow and white. The wastegate regulator valve N75 connector wires are black/yellow and brown/blue. This is what the Bentley manual schematic shows for 1995, 1996 and 1997 TDI 1Z engines. I'm still not sure what my solenoid is called*, but the wires are yellow with a black stripe, and brown with a black stripe - could be very dark blue :-) In any case, it doesn't do anything whether connected or not - nothing opens or closes or changes. I had it on the kitchen table this afternoon and tried WD40, 12V, 24V ac and dc and a variety of other torture devices - it just reads 269 ohms and I am going to break it open with a meat cleaver on Tuesday when my new one arrives.

The manual is not as clearly written as it should be. The manual says that (even though one is described)...TDI engines do not have a wastegate. The turbine blades speed is controlled by vanes inside the turbine housing. That is what the Wastegate actuator controls.

Interesting

On your final thoughts... one hose provides negative pressure (upper side of wastegate )and the other hose(bottom side of diaphragm) provides atmospheric pressure. They are on opposite sides of the wastegate diaphragm. So it is the exact opposite to what you were visualizing.
OK - but mine seems to be like the one in the picture I linked to, with the pipe from the turbo compressor side (~+10 psi?) going in below the diaphragm, and the line from the vacuum pump (via N18) going in above the diaphragm. I will get the hang of it one day...
The ECM actuates the Boost Pressure control valve (inside the turbocharger) via the wastegate regulator valve N75 to move the turbine's vanes to a more closed angle to increase boost(higher turbine speed) when the ECM detects increased engine speed.

When the ECM senses lower engine rpms and the vanes are moved to a more closed angle by the wastegate regulator valve N75, reducing exhaust gas pressure and turbine speed, but allowing more exhaust gases to flow and extracting less energy from the exhaust gases.

I just looked at the manuals DTC code chart. a bad EGR vacuum regulator solenoid valve N18 will cause reduced power output and black exhaust. Interesting - but I don't have black exhaust emissions that I have noticed. I'll report back when I have corrected the known defects - N18 and wastegate actuator.

Thanks again, OD

* technically it is a 191 906 283 A

[Crasher]

It isn't called an N75 valve on the AAZ as the turbo isn't controlled in the same way as a 1Z TDI.