bought a '90 tsi a few weeks ago. Evo III exhaust manifold, s16G , 2.5" piping through sparco fmic, MAF-T, and 3" exhaust from turbo. I drove it for about a week and it'd hit and hold 15 psi fine. Put it away for a week and half, and the only change to the car was new manifold to turbo exhaust ring, new manifold/turbo gasket, and new air filter. Now it climbs to 20 psi everytime I come onto it. Since I'm still working with 460cc injectors, it starts missing at 16 psi, but it hits 20 before I can get off the gas. I've adjusted the mbc all the way out so that it should build stock boost at most, but it makes no difference whatsoever.
I want to check the wastegate and actuator now. Should I be able to move both by hand? What's the best way of 'testing', to make sure they have stiffened up for some reason in the week and half it sat.
My only other possibility is boost creep I assume? Any other thoughts?

A simple way to determine if it's boost creep: Disconnect the actuator from the arm on the wastegate flapper. wire the wastegate open, and go for a drive.. see how much boost you can build.

Remember though: If you wire the arm ALL the way up, the wastegate will be open more than if the actuator was opening it. The actuator only moves ~ 1/4" - 1/2" or so.

Does it 'shoot' up to 15, and then make it's way to 20 more slowly? Or just hit 20?

You 'could' be getting more air with the new filter (I doubt it), or the ring could have something to do with it. The only theory I'd have is that it directs more air onto the turbine and past the WG opening? But that sounds pretty weak.

ya, gets to 15 pretty quick, and then slowly( as compared to how fast it gets to 15 ) continues onto 20, by which point it's pissing and farting and I'm getting off the gas

Was any ring in there beforehand? I remember removing mine, but was doing some port work at the time and had everything so that there would have been minimal (if any) leaks.

ya, the one that was in there appeared to have been beaten in with a hammer and was very disfigured. I was getting new gaskets for there anyways, so I figured I'd replace the ring.

Is it possible you've fixed a pre-turbo exhaust leak?

Have you double checked your MBC connections? (To make sure they are "correct" and not necessarily "the way they were" if you know what I mean..)

I definitely fixed a pre-turbo leak, the gaskets on both ends of the manifold were destroyed or missing all together. The mbc is plumbed fine as far as I can tell.

Not possible that the MBC has the inlet/outlet swapped?

nope. These lines have not been disconnected since i got the car... and boost was fine before fixing up the pre-turbo leaks. Am I to understand from everyone's questions, that I 'should' be able to hold 15 psi with my set up?

You can hold as high a psi as you want (within reason) with almost ANY setup. Controlling it can be tricky with higher flows.

We're just giving you the possible causes for the change. Your turbo could have been losing enough pressure from those leaks that it held steady at 15psi. Now that the leaks are gone (or reduced), that extra flow is trying to get out of the wastegate, which isn't big enough, so it's forced through the turbine.

Is it easy for you to pop that turbo's exhaust housing off and port out the wastegate opening?

A small 16G shouldn't "creep" to 20psi because of the wastegate opening. the stock opening is plenty big enough.

The problem probably lies in the boost source - boost actuator "system".

"These lines have not been disconnected since i got the car... " Is it possible that the lines have been hooked up wrong since BEFORE you got the car, but the pre-turbo exhaust leaks were hiding it?

What you've explained here is my understanding of boost creep... which is what I'm asking if it could be...haha.

The plumbing for the mbc is correct... whether it's working properly or not is still unclear. I'm dealing with a transfer case issue at the moment, so I'm not driving it or testing any theories for few days.

Definitely 'could be', I remember people getting boost creep on 16g turbos before, but usually with much smaller exhausts than 3".

It's pretty easy to check your MBC system. Just disconnect each rubber tube and blow/look through it. See if there's any obstructions. It'd also be nice to check those hoses for cracks/leaks. Usually you'll have a tiny pinhole to bleed off residual pressure, but a large one will cause your WG to open late, if at all.

You should also put a compressor on your WG actuator at 6-9psi or so and see how far it opens. Make sure the WG flapper arm is opening all the way.

Make a diagram of your MBC connections as well and put it up here. Steve would best tell you if there's something that can be done better.

I am no expert, but I always thought that boost creep was a result of the exhaust being too large and free flowing, not the other way around? As it was explained to me, boost creep was not from exhaust being FORCED through the turbine because the wastegate wasn't handling the flow, but from it being EASIER (because of the large free flowing exhaust) for the exhaust gasses to go through the turbine rather than through the wastegate?

Troy, I think your memory isn't serving you well. Our 14Bs and 16Gs were happy with the stock exhaust, it was when we installed the 3" exhaust that we would suddenly have boost creep issues. The wastegate opening wasn't proportionate to the increased exhaust flow, causing the boost to creep. That's when we started hogging out that wastegate opening.

well look at that... learn something new everyday I've misunderstood boost creep all this time.

So who is right?

http://www.ktarry.com/pub/techhtm/dsm_mbc.htm

or

http://www.dsmtuners.com/forums/articles-turbo-system-intercooler/237982-best-way-install-mbc.html

I have used Kyle's route with success. The manifold is the best place to get your source. From Kyle's explanation:

You HAVE to use the intake manifold is you want proper boost control. Why is that? The manual boost controller regulates the amount the wastegate is open based on the pressure at its source. Since you want to control manifold pressure, you want the MBC and the WGA to be recieving pressure directly from there.

Using the nipple or source on the turbo doesn't account for pressure drop through your IC.

Ziggy: I'd say that's an expert explanation of boost creep.

Thanks for the "endoresment" Troy. Sure, Derek if you want to post up a daigram, I'll let you know if I'd change anything.

I'm with Michael on how to run it though. Kyle is one of the DSM guys that has been doing experimentation/testing the proper way (isolating things, repeating results, etc) and has proven to know his stuff.

I have mine set up exactly as Kyle suggests.

Heh. Now you just have to learn how to spell endorsement, Steve. *Laugh* Okay, so the air can't get out the wastegate fast enough OR it's easier to go through the turbine... To me that's 6 of one, half a dozen of the other? Enlarging the wastegate fixes it either way.

My memory is degrading a bit, but I do remember that plumbing an MBC from the manifold or a source vacuum line is the way to go. Much 'smoother' source of pressure as well. Right at the turbo you'd see all sorts of spikes.

Gah. I'm stuck in the land of VW, "You can't go with a larger than stock exhaust! Your turbo will spin so fast it'll EXPLODE!!!"

Just out of curiosity Troy, using what theory or mathematical equation did you use to come up with that idea?

Essentially, what you are saying is the pressure from the turbo at the J-pipe is significantly different than the pressure at the intake manifold.

Seems to me, any pressure spike at the J-pipe would be affected at the intake manifold.

Sure, you get into big intercoolers and huge pressure drops, however IIRC, the best place to tap your MBC is as close to the turbo as possible.

Hmm... you should get ahold of PTE, FP, Garrett etc. and share your pressure theory, this way they can stop drilling and tapping their compressor housings for a boost source! They had it wrong the whole time!!!

Huh?

Ryan, did you read Kyle's article? The logic is simple.

"Okay, so the air can't get out the wastegate fast enough OR it's easier to go through the turbine... "

Unless, the problem is AFTER the wastegate. ie: there's a vendor out there that "solved" boost creep issues with their turbos by joining the paths that the wastegate exhaust, and turbine exhaust take before the 02 housing.

Essentially, what they did was create enough turbulance to restrict the flow of exhaust. It got rid of the symptom, but it's not how I'd try and fix the problem. Kind of the same same thing as narrowing a 3" exhaust to 2" to stop boost from creeping.

BTW: You missed "daigram" in my last post.

Derek: have you tried running with a line going directly from a boost source to the actuator, to rule out the MBC?

It's amazing that almost 20 years after these cars were released, we still can't agree on the right way to hook up a boost controller!

I know a few guys on here are adamant that the intake manifold is exactly the *wrong* place to take your MBC signal. The argument is that if you're at part throttle, there can be a big pressure differential between the intake manifold boost, and what the turbo has to produce to get it there.

Nick Boers used to post on this alot, here's one of his posts for example. (here's one).

I've never measured the "before throttle plate" vs. "after throttle plate" pressure to see if there's a difference, but my car drives better with the MBC tapped at the compressor outlet. The Mitsu engineers did it that way too.

I haven't done anything since starting this thread as the transfer case has been sitting on a bench waiting for the output shaft seal to arrive. I'll be back to real life testing this weekend hopefully.

The only way to settle this argument, is to buy an EBC

ironically, there is one in the car that was unhooked for some reason... I haven't had time to look at hooking it up as it's just the unit sitting in the dash right now with no hookups in the engine bay.

Depedning on the model, they can be very dififuclt to set up. Maybe the prveouis owner had gievn up.
It could also be that you're missnig the soelniod box, so the head unit has nothnig to cnotrol.

Rob, if you read what I quoted, you would see I was referring to Troy's post about where to tap a boost controller in. Intake manifold or close to the turbo.

I know, Ryan.
My post was more of a commentary on the fact that your post contradicts the expert opinions above it.

In the end, this one comes down to preference.
I like Jeff's quote:
"It's amazing that almost 20 years after these cars were released, we still can't agree on the right way to hook up a boost controller!"

So, am I wrong then?

Edit: NVM, I read the post.

So then my question is, why do most common turbo setups have a boost source directly at/after the turbo if connecting to the intake is the best source?

Hey, I learned something today.

Because they are simple setups, and they don't ask for much
Often it is just a direct line to the WGA (or with a bleeder valve in line as on a stock DSM).

Now get into more complicated setups with EBCs, and you learn that the controller gets its boost reference (signal) from the manifold, and it only uses the compressor line to actuate the wastegate.

An MBC uses a single pressure source for both duties (signal and actuation), and therefore you have a conflict of interest.
Some people prefer to use the manifold and others the compressor. Neither of these people are "wrong". The MBC is what's wrong. Ideally, you should use the manifold for signal and the compressor to actuate, as does an EBC.
In DSM-land though, it's often cheap & fast, so you can assume that things are not always ideal.

Ok! Well, that clears things up.

Going to go pull my foot out of my mouth now.

I would just like to add, back when I was running an evoIII, internally gated with a MBC I had ran it with the MBC sourced off the BOV line/mani & off the jpipe. I can say that for me, boost control was much better of the jpipe. Boost spikes were much less & the boost control in general was alot more stable. This was on the exact same setup, just changing MBC source location (had it temporarly tee'd in the BOV line before I added the jpipe boost source).

I have actually noticed a decrease in boost spike since moving my pressure source from the BOV/Intake to the Jpipe. I thought the theory was to measure the boost pressure at the closest location to the source (turbo) so that the actuaor could respond more quickly to the changes in source pressure. Rob, if what your saying is true about EBC how should the lines be run. Now io have 1 line form jpipe to Greddy solenoid and 1 line form actuator to solenoid. How does the Inatke pressure source come into the equation for this setup?

^^^
This might depend on the model of EBC, so perhaps my explanation isn't 100% correct.
Does your EBC not have a provision for a signal line (separate from the compressor signal)? In that case, I think it is your solenoid box that communicates the boost level to your head unit.
So, you'd be using the compressor for both signal and actuation. This is fine though since the EBC would be calibrated for such a configuration, and probably has a set-up mode to dial in the pressure differential.
The main thing is that you're using the compressor to actuate the gate (for best response).

Ok, so using the compressor/J-Pipe with an MBC to actuate the gate is usually the safest, easiest and most correct way to run it right?