weak VNT spring?

[ChuckV309]

I am not getting full boost pressure on my 1996 B4V. It appears to be due to the VNT spring being weak and allowing the boost to be released too soon. I have checked all parts of the pressurized system and everything is good (N75, hoses, etc), but can only get about 12 psi. I have new DLC 1019 injectors and tune from KermaTDI. From working with Charlie from Kerma, he feels the problem is the VNT spring and recommends putting on a new turbo.
When I put pressure to the VNT it starts to move at 5-6 PSI and is at full travel around 9-10 PSI.
My question is can I do something other than a new turbo for a while til I get the money for a turbo? The car drives fine, just not getting full boost for the tune and injectors when at full throttle. I was thinking about using some kind of pressure regulator to control pressure to the VNT. Like a small one used to control air pressure to an air brush. I know it would be trial and error till I get it dialed in to limit pressure to 18 psi. The cost would be $0 as I have a mini regulator I could steal from my air brush for a while.

Any ideas or suggestions?

Chuck

 

[Abacus]

You don't have a VNT, you have a wastegate. That you can get it to move with pressure tells me it's still a wastegate turbo since the VNT turbo's use vacuum.

If the 'spring' were weak (it's a diaphragm) then you'd be seeing too much boost rather than too little. You have something opening the wastegate when it shouldn't be.

If Charlie from Kerma is telling you this, find another person to ask because he doesn't know your car well enough to make a diagnosis.

Even if your N75 tests fine, replace it. I have had many partially fail so they appear to work fine on the bench but don't under actual conditions.

 

[ChuckV309]

The N75 is new. I thought that was the case with our turbos, but he is supposed to be an expert for tuning these. So does it use pressure to open or close the wastegate?

 

[Abacus]

Pressure to open the WG to dump excess boost.

 

[16vjohn]

...my 1996 B4V...... working with Charlie from Kerma, he feels the problem is the VNT spring and recommends putting on a new turbo....

This is very concerning coming from people we normally trust with these cars....

x2 Abacus, you have a wastegate.

 

[GTiTDi]

wow. I know the saying " forgotten more than you will ever know" but that is too elementary to get so darn wrong...

 

[ChuckV309]

I agree. So, is there anything you guys feel I should check? Do those pressures and movements sound right that I listed in the opening post?

Chuck

 

[rdkern]

I wonder about the tune - errors happen.

Could you have swapped the pressure lines from the N75?

12 is what you would expect stock. Tuning can go up from there, but over 20 on this turbo is, imho, extreme for the turbo.

If the N75 were weak, I'd expect too much boost, but I guess it could stick open once activated.

I don't know what else would cause this, other than swapping the pressure lines, or the tune.

 

[ChuckV309]

I replaced the lines one at a time on the N75. As far as the tune, this is the second set of chips from Kerma. I sent in graphs to them after the first set, so he could adjust some of their settings. The fuel is definitely there, cause after about 3/4 throttle, there is a definite black fog out the back.

Here is how it is operating during acceleration:
Cruising at 45 MPH boost around 5-6 psi, full throttle, boost jumps to about 9 psi and then slowly climbs about 1 psi every 1.5 seconds to almost 12 psi.

Chuck

 

[Digital Corpus]

Let me dig around for some specifics about crack and opening PSI for the wastegate. My previous owner hammer modded the IP way down and adjusted the WG actuator for huber pressure and gave me an additional 10 whp and 15 ft*lbs of torque.

I'll post back soon.

Edit: this was a time before I linked to all my source threads. Anyhow here is the result of my research.
http://forums.tdiclub.com/showthread.php?t=399988

Your pressures are normal. I'd advise looking for a boost leak. Have a look at the aluminum pile coming out of the turbo. If it's not supported, it can rub on the EGR cooler and create a hole.

If you don't find and fix the boost leak, especially with a tune, you're causing the turbo to speed up more than it should.

 

[ChuckV309]

For a brief test, I plugged the line going to the wastegate and went for a careful drive. My boost would hit 25+ psi and with some careful foot adjustment, I was able to sustain about 18 psi during acceleration. I don't think there is a boost leak. Not sure if this tells anything or not, but nice to know I can make and hold that much boost.

Chuck

 

[Digital Corpus]

Since you have VCDS, could you pull a log of group 11 from 1500 to redline, or as close as you can get to it, and post it here.

 

[ChuckV309]

I will try to get one tomorrow afternoon.

 

[ChuckV309]

Couldn't get the graph today, and now probably not for the next couple days. Big snow storm coming through. Will post as soon as I can.

Chuck