A4 B6 1.8t Waste Gate Actuator diaphragm leaking, running lean - need advice/parts

[markcm]

Hi folks,

My 04 A4 1.8t Avant has been running a bit lean for a while, long term fuel trim varies around 7-10%, plugs and O2 sensors are white, pinging when hot... I replaced the Mass air sensor, the O2 sensor and the Kombi valve, none of which helped.

Now I've pulled the vacuum line at the N75 valve and pressure/vacuum tested the line to the waste gate actuator and found it leaks so it seems the diaphragm in the waste gate actuator has failed. I will check the vacuum line closer although the materiel looks pretty good so I don't think the hose has cracked, I'm pretty sure its the diaphragm.

I have searched far and wide for waste gate actuators and only see $200 aftermarket options from ECS or $30 Chinese options from Roth or ebay, don't these things ever fail? What do people typically do when the do fail? I found a good DIY which pretty much says you have to pull the turbo to replace the WGA; one person said the did it without pulling the turbo but it was a lot of work getting at the bolts.

The car seems to run fine with exception of pinging, particularly when hot (80+), it still has ~12psi boost and boost seems to be smooth.

Does anyone have any good links for a OE quality replacement or does anyone have a used actuator they'd sell? Or, any general suggestions on this subject? How do I adjust the replacement when I get there? Do I just run it up until it closes the Penny valve and then give it just a tiny bit more tension for pre-load?

[A4SoftWalker]

You can start at this site ATP Turbo or call/e-mail them up if its too confusing.

[diagnosticator]

You can buy a genuine BW actuator from any BW distributor or BW authorized diesel fuel injection/turbo repair shop.

[walky_talky20]

How bad is this leak, exactly? On a B6 1.8T, a leak in the diaphragm shouldn't make the car run lean. Even if the leak is fairly large.

- The boost may be higher at some points, but the ECU should adjust for this (less N75 duty to meet a certain boost request). If the boost is higher than it can adjust for, it will throw a code and go into limp mode.
- Even if the boost runs a little higher, the ECU will adjust fueling to compensate. It knows the boost pressure and air flow at all times.
- If we consider the last point, some air mass is actually being lost through the leak (a very tiny amount, but still). This would result in a rich condition - if anything.

So, unless the diaphragm leak is actually causing a real boost control issue - I don't think you need to go after it. I think you'll find that your lean issue is somewhere else.

[markcm]

Good points...

Where does the "pressure" come from that the N75 controls? The diaphragm is fairly torn, I can blow air through it without much resistance.

The car runs pretty smooth, even with this in mind and it seems to boost about 12psi which I think is right for a stock AMB 2004 1.8t?

I do have MIL light on for "incorrect secondary air flow". I just replaced the kombi valve because my secondary air pump was full of condensate. Now my pump is noisy from being full of fluid so but I cant tell if the CEL is from the pump going out of another valve somewhere sticking open. I tested the Kombi by turning the secondary air pump on with VAGCOM; no air was flowing out the tailpipes; I put a vacuum on the Kombi and air began flowing out the tail pipes so that circuit seems to be working correctly.

[walky_talky20]

Pressure supply to the N75 comes from the turbo compressor housing.

12 psi on the gauge is probably a little high. The stock value is actually 10.5 or 11, I believe. A log of boost request vs actual (and N75 duty) would be needed to see if boost is out of control or not. When overboost occurs, the ECU's first step is limp mode (reduce N75 duty). If it still overboosts (ECU cannot get the gate to open) then it reduces the throttle plate angle. You would need to log to see what it's doing.

That said, if you can blow through it, that's not good. The leak can only get worse, so replacement of the actuator is advisable. Since you know that is bad (and you have replaced other EFI equipment), it would be advised to fix this known problem first before continuing with diagnosing the lean mix.

I haven't changed an acutator on-car, but it does look tricky. I have disconnected the shaft form the turbo with manifold in place. That isn't too bad. The top bolt for the actuator-to-compressor looks pretty reasonable too. But the bottom bolt is in jail. And the coolant line bolts to the actuator too. And that bolt looks hard as well. I think it's doable without pulling the manifold, but you will have to get creative. I think removing the turbo brace and oil drain line will fix most of the access problems.

[markcm]

Thanks again, I'm going to start with replacing the WG actuator as you suggested. I found a pretty good write up on the process here if anyone else is interested.

[walky_talky20]

Just an add-on to that write up - I like to adjust the actuator rods to a specific pressure. Basically I apply a metered amount of pressure to the actuator, and adjust the gate so it is just cracked (able to spin the flapper) at that pressure. I usually adjust to 5psi, which is just slightly tighter than factory (generally 3-4 psi). The ECU can adjust for this easily, but I'd rather it adjust down, than hit the end of the table trying to get the boost up where it should be. If you're trying to hit 20psi, a crack pressure of 3psi is a little weak.

[markcm]

After a closer look, I think I mis diagnosed the WG actuator.

My car still has most of the original small one time use hose clamps (at 132k), next I think I will look at the diverter valve.

The car runs fine, it's just 7-10% on the fuel trims with white plugs and pings when ambient overt 75 degrees or so.

I have a fresh Kombi valve and old one seems good, I tested it for proper operation too, fresh MAF and fresh O2 sensor. All my small vacuum lines seem healthy, they are solid rubber, no cloth braiding on them.

It all started with the plastic pipe the comes out of the crank case below the intake manifold breaking; I replaced all that and it seems sealed up properly. Then my secondary air pump filled with condensate, I replaced it and the Kombi assuming it was to blame. I still get a "incorrect secondary air flow" Check engine light.


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[2stroke]

I like to adjust the actuator rods to a specific pressure.
Basically I apply a metered amount of pressure to the actuator, and adjust the wastegate so it is just cracked (able to spin the flapper) at that pressure.
I usually adjust to 5 psi, which is just slightly tighter than factory ( generally 3~4 psi ).
The ECU can adjust for this easily, but I'd rather it adjust down, than hit the end of the table trying to get the boost up where it should be.
If you're trying to hit 20 psi Boost pressure, a crack pressure of 3 psi is a little weak.

I have just tested two K03-29 Turbo's and both of them had a cracking pressure of 0,2 Bar / 2.9 psi
( both with connected wastegate flapper. )

Acording to technical specifications from BorgWarner the factory setting cracking pressure for K03-029 should be -----> 0,37 Bar / 5.366 psi

Is it ok to just adjust the nuts on the actuator rod until it reaches 0,37 Bar / 5.366 psi ?

[Cybersombosis]

Yes.

[2stroke]

Yes.

Stroke length of the actuator arm: (measured from the time it starts to move until it does not move any more)
~16 mm. / ~0.629 in.

Cracking pressure:
~0.20 Bar / ~2.9 psi.

Maximum open pressure:
Old: ~0.6 Bar. / ~8.7 psi.


But if I adjust the position of the nuts on the actuator arm, so does the total range of motion for the actuator arm also change !?!?
and it's not good, or is it ok ?