TheSamba.com :: View topic - What is going on with my AAZ boost pressure?

Mon Jan 29, 2018 2:50 pm

Hi.

I have a 1.9TD AAZ in my vanagon. I have a home made boost controller that has worked great for a few years now. My max PSI is around 20 psi. I have the fuel turned up in the injection pump, and I have the boost pin from a 1.6TD in the AAZ injection pump.

This has been a great combination for producing good but not excessive power for the van. I also have a boost gauge and EGT gauge.

So recently, the boost pressure has not been holding to what it previously had been. I can still get the same top pressures, but it does not hold that pressure, even under load. The pressure will spike, then slowly taper down towards stock pressure. This causes less power, and my EGT to climb.

I thought it might have been my boost controller, so I took it apart and rebuilt it. Didnt fix it. Then I made another one, completely new. even tested it with a bicycle pump to ensure it was working. Again no change in how my boost pressure has been operating recently.

The other odd thing that happens, my turbo sometimes seems to neglect that it has a wastegate, and builds over 25 psi and holds it. I then have to back off on the throttle, so I dont overproduce boost pressure.

But then if I give it a quick full throttle, jolting/spiking the boost pressure towards 30 psi, it seems to fix its problem of the wastegate not opening, and goes back to its current operating state. This again being not holding the boost pressure I have set in the boost controller.

I also find, it is more likely to hold close to my desired boost at lower gears under load, than higher gears under load.

I used to cruise down the highway in 5th gear @ 16-18 psi. Now I am lucky to get 14 psi but usually the pressure tapers off slowly to 11 psi.

Any thoughts? I am leaning not towards something being wrong with the waste gate or the actuator. However, have limited experience dealing with turbos.

Thanks!

Mon Jan 29, 2018 2:59 pm

What turbo? When you say wastegate is it the VNT vane type or something else?

Mon Jan 29, 2018 6:07 pm

It is a KKK turbo.

It looks like this

Mon Jan 29, 2018 6:10 pm

How old is the turbo?
It sounds like it needs some attention. First thing I'd do is remove whatever you need to to get you fingers on the impeller and see if it spins free or wiggles side to side or in and out.

Mon Jan 29, 2018 6:17 pm

You also might need to take apart your wastegate valve and clean out the carbon and/or lap the seats with abrasive.
Also regarding the impeller shaft wear, if it gets too loose it starts to chew itself up and you need a new turbo. Best to have it professionally rebuilt periodically, I think 70k miles is about it for the KKK.

Mon Jan 29, 2018 6:35 pm

I cant say for sure how old the turbo is. it might have 230K Km on it.
Last time I had the hose off, there didn't seem to be excessive play. That could have changed.
But I'm sure it spins freely. Otherwise it wouldn't make any boost. Correct? Or do you mean that there could be resistance of it spinning?

Mon Jan 29, 2018 6:54 pm

I can't see the mechanism in the picture. The VNT type gets vacuum from the vacuum pump via the N75 valve pulling the turbos internal vanes so you have full boost available. If the computer senses overboost the N75 valve bleeds vacuum to the atmosphere and the internal vanes bypass excess boost out the exhaust.
I imagine your boost controller is the management boost device. So, for testing the turbo, I would temporarily disable the "wastegate" at the turbo and drive. If you maintain your boost, then you know the turbo itself is fine and you need to look at your overboost management system.

Mon Jan 29, 2018 7:18 pm

There is no computer. The AAZ is purely mechanical.

As far as the boost controller goes, I am using a ball bearing with a spring to form a seal against a 1/4'' brass fitting. I use a bolt to compress the spring which controls the pressure on the ball bearing and thus the boost pressure needed to open the boost controller and allowing pressure back to the actuator.

My boost controller looks similar to this

https://www.google.ca/search?q=how+to+make+a+boost...#kpvalbx=1

Mon Jan 29, 2018 7:21 pm

I am pretty sure my turbo just builds pressure, then uses a hose to relay that pressure to the actuator with a spring. When the set pressure is reached, it opens the waste gate. So my boost controller allows more pressure to be produced before allowing that to be passed on to the actuator.

Mon Jan 29, 2018 9:10 pm

That kind of mechanical adjustable "boost controller" is often called a "Dawes device". They are a very crude way to control a turbo that does not use electronic boost control. They work okay if the parts used are reasonably good quality, but it is critical to keep the pressure hose into the device and the hose connecting to the waste gate actuator as short as possible to prevent boost spikes. The reason for that is the boosted air to the Dawes Device needs to force the ball in the device to move quickly and then the boosted air passing the ball valve needs to quickly fill the waste gate actuator before overboost spikes occur. The device also needs to be large enough, in terms of the bore diameter, to allow the waste gate actuator to move quickly.

I suspect that in your case, the real problem is a very sticky waste gate valve (and/or actuator) which could be a result of exhaust soot in the turbine housing and waste gate area. The other thing to check is whether any of your Dawes device plumbing is kinked or leaking. Finally, the diaphragm in the waste gate actuator can fail slowly with a small leak. Check the actuator for leakage using both pressure and vacuum.

I think you should also check for boost leaks as these can cause funny running problems like you describe. Engine movement can open and close leaks/splits in the hoses conducting the boosted air from the turbo to the intercooler and to the intake manifold, giving rise to otherwise inexplicable symptoms like those you describe.

Mon Jan 29, 2018 9:43 pm

Thank you for explaining the workings of my turbo. What you suggest sounds like it could be the culprit to my problems.

If the waste gate or actuator are acting up, then there may be other problems to come as well. I think I will look into getting a rebuilt turbo.

Tue Jan 30, 2018 5:25 am

You may want to check the condition of the waste gate linkage. Inspect the pins and make sure the pin holes haven't turned into slots as well.

I have to say, my AAZ Westy had a KKK 14 and getting it to exceed 14 PSI was difficult. I also had a very similar home-made controller and it worked pretty well. I did get it to 18 a few times but there's not much air volume at that speed so it's simply hard on the turbo and EGTs climb very quickly (not enough air).

You didn't say or I didn't catch it, what size your turbo was. I believe a KKK 24 might be capable of hitting the boost numbers you have mentioned.
Still, hitting 20+ often, especially with as many miles you have done might be causing it to act erratically.

I have done a lot of messing around with my Holset HE-200 and ended up fixing the wastegate to an always closed condition. By tweaking the fuel screw on the pump and adjusting the star wheel in the LDA (based on my pin grind), I am now hitting 20-22 PSI only when I floor it. My EGTs very seldom reach 1250 F and I have little to no smoke.

To be clear, I am no turbo expert by any stretch. I leaned heavily on members suggestions from this and other forums (the IDI forum is a great place for turbocharged AAZ info). I also have a huge water to air inter cooler, a water storage tank, and extremely short piping runs. I simply kept at it until I reached nirvana :D Now if I could just fix the leaky 50° valve cover :shock:

Tue Jan 30, 2018 5:28 am

I get that it is mechanical. Was trying to explain how it should work using the stock style as a reference. Disable the "wastegate" temporarily and drive it. If you get and maintain full boost, turbo is fine. Problem is in your boost management.

On the other hand, if you can't maintain boost, problem is in the turbo or plumbing as suggested.

Tue Jan 30, 2018 11:13 pm

Yes. It puts out a lot of boost. I could hit 30 psi if I really pushed it.

Wed Jan 31, 2018 6:59 am

beach_creature wrote: Yes. It puts out a lot of boost. I could hit 30 psi if I really pushed it.

You may want to check your gauge

Fri Feb 02, 2018 3:13 pm

beach_creature wrote: I think I will look into getting a rebuilt turbo.

Try a different boost gauge before you do anything.

If the gauge isn't the issue, a small crack or pinhole in the line supplying boost pressure to the wastegate actuator would cause the symptoms you've described. If this is the problem, you could pay for the fix with a $5 bill, and get change back. Problems with the wastegate actuator diaphragm could also cause your symptoms, and be fixed with a simple cleaning or replacement.

The wastegate actuator is the gold colored thing in the top right of your turbo photo. There will be a small (3mm) hose on the barbed fitting visible in your photo. It would only take a second to visually inspect that hose, to make sure it is connected at both ends, and has no obvious holes or cracks. You can test for leaks with a bike pump and some ingenuity (a piece of duct tape might be all you need). You can also use a bike pump to put pressure to the fitting on the wastegate actuator. See what PSI it takes to move the little arm on the wastegate actuator. There is a diagphram in the actuator that can fail--if it has a hole in it, the result will be the turbo boosting higher than you want.

See the hose in your turbo photo? Check that too.

Same deal with your homemade boost controller. Pull that apart and make sure it isn't all gummed up or something.

All of the above should take 30 minutes at most and cost nothing. Personally, I'd rather do that than throw money at a new turbo. Could be a real simple fix, like a bad hose, or something easy and relatively cheap, like a failed actuator.

MarkWard wrote: Disable the "wastegate" temporarily and drive it.

Just to make sure you understand what will happen if you do this, without a functional wastegate, the boost pressure will be controlled by your right foot. With a load on the engine, the turbo will continue to boost until you let off the accelerator. If you power up a steep hill or something, you can blow stuff up if you aren't careful.

Tue Apr 10, 2018 10:14 pm

only now starting to look into it again. It had briefly started working fine and now back to just putting out 28 psi boost at full throttle.

I used a bike pump on the waste gate actuator and it starts to move at 20 psi and completes the opening at 30 psi.

These pressures reflect what my boost gauge is showing me. So can I assume there is a problem with the actuator or maybe the wastegate itself sticking and causing the problem?

Anyone know the proper pressures the wastegate actuator should be opening at?

Thanks!

Wed Apr 11, 2018 6:29 am

You never said what model the turbo is. Is it a k-14 or k-24?
I'm no expert but my AAZ had a K-14 on it when I bought it and I believe it was the stock turbo. At 14 psi it's pretty well maxed out according to the curve.
There is a maximum amount of air (pr pressure) a turbo can move and hitting 30 psi with a turbo of this vintage is amazing stuff.
I mentioned previously that your linkage my have slots instead of holes where the pivot pins are. Have you checked that?
There is a huge amount of pressure on those pins and over time they cut slots into the linkage plates - that may also explain the intermittent nature of your issue.
I can't answer your question with any degree of knowledge, but I believe a stock K-14 opens the gate at 10 PSI

Thu Apr 12, 2018 9:03 pm

Here is a photo of the tag on my turbo. I am also posting a picture of another turbo I have from an AAZ. (appears to be the same turbo as I have in my van. this other turbo does not produce boost, and the wastegate actuator does not work. it has a leak in the seal. So i can not use parts or swap the turbos)

Fri Apr 13, 2018 5:13 am

Hmm - appears to be a K03. A google search reveals some folks are hitting 22 psi or more - amazing. The history of their longevity is not good though - especially at those pressures. Reading more, also shows that they "spike" to high numbers and settle back to 17 or so. Not sure why that would be, but I am no turbo expert. Might be worth a visit to the VW Vortex site?
Personally, I'd back off on your pressure goals till you save up for a newer turbo made to run at those pressures - or you might be running 0 psi sooner that later.