06 Jetta BRM, rebuilt turbo runs bad unless

the hose to the VNT actuator is disconnected. I had the turbo rebuilt by a reputable turbo rebuilder, installed it, and the car runs like crap. No power until 2200 rpm, black smoke, rapping noise, acidic smell from under the hood like the converter is overheating. It ran better BEFORE the rebuild.
If I remove the hose from the VNT actuator it's a whole different animal. Tons of smooth power, no significant smoke or noise. I assume removing the hose keeps the turbo vanes closed so it builds full boost all the time. Thats great but if not careful could damage the engine if you give it too much boost so I want it running like it should.
Ran some tests. Put vacuum to the actuator and the rod moves smoothly and holds vacuum. Checked the solenoid and it puts out good vacuum to the valve. Do have the code P0299 low boost. What to check next? Could the actuator rod be out of adjustment? Don't rebuilders bench test and adjust that?

With out the vacuum hose hooked up it runs the turbo vanes wide open at the no-boost position.
Sounds like the vanes are closed down too much. Sounds like your reputable rebuilder may not have tested it before delivering it.
Try the zip tie mod test:
https://www.myturbodiesel.com/wiki/turbo-stop-screw-adjustment-tdi-engine-zip-tie-engine-hesitation/


Looks nice, though

JETaah said:

With out the vacuum hose hooked up it runs the turbo vanes wide open at the no-boost position.
Sounds like the vanes are closed down too much.

Click to expand...

I think just the opposite. Without the hose the vanes must be closed since it has plenty of boost.

On your turbo, when you apply vacuum does it draw the actuator rod inward or push it out?

If I remember correctly it pushes out.

It should. Just wondered if the actuator got substitued with a more typical configuration.


Is this car tuned?
On some of the BRMs that I've worked on, the turbos will boost even without the vacuum attached. I believe that it was a flaw in the manufacturing process where the vane lever was welded in the incorrect position.



No vacuum = open vanes...and should not produce significant boost unless the vanes are positioned where they can not be put in the wide open position.

Did you give a read of the link that I posted above? It would provide a better explanation of what happens when the vanes are closed down too far because of the lever stop screw is not adjusted correctly.


Here is a post by Jeff from Rocketchip tuning regarding the BRM's turbo
https://forums.tdiclub.com/showpost.php?p=4489645&postcount=3

Yes I read that link. It goes from about 960 to 1050. Now a question about the N75 valve. Is this a solenoid, i.e. on or off, or variable vacuum? Because when I do this test with a vacuum gage in the hose to the VNT actuator it reads either 0 or 25 in. so that's expected. But outside the test, at idle, it shows 17 in. Is this normal? Shouldn't it be 0 at idle so the vanes are closed?

You still don't get it.
no vacuum = open vanes = no boost in a properly functioning turbo.




17in/hg is about right for the idle vacuum...sometimes higher. 17-20 is a correct range and the lever should be on the stop screw.

The N75 valve is a pulse width modulated valve. The ECU varies the duty cycle for the N75. The valve alternates between venting and applying vacuum to the actuator to vary the position of the lever.


17in/hg = is vanes closed ready to boost until there is more boost than requested. When there is more boost than requested it drops the vacuum to start opening the vanes.


Re read the myturbodiesel link.

JETaah said:

You still don't get it.
no vacuum = open vanes = no boost in a properly functioning turbo.

Click to expand...

I don't. If that is the case, why does it have so much more power (boost) with the vacuum line off? And with the line connected it has little power, little or no boost and black smoke?

JETaah said:

The N75 valve is a pulse width modulated valve. The ECU varies the duty cycle for the N75. The valve alternates between venting and applying vacuum to the actuator to vary the position of the lever.

Click to expand...

Ok thanks for clarifying, I was thinking it was either open or closed. I'll look at the zip tie mod link again.