Boost fade
 

I have a 96 Tsi with a 3" exhaust and an FP T-28 turbo. I run about 18 lbs of boost, but it doesn't hold - it fades to 14 by redline.

I've checked for boost leaks, 99% sure there isn't one. I've changed boost controllers, same thing happens. I actually tried a broken boost controller too and it didn't limit the bost, so it went to 25 almost instantly at 3500 rpm and I let off.

What else can cause this? I assume the T-28 can hold over 18 until redline, so I doubt that's the issue.

Any ideas???

Re: Boost fade
 

Fill with c16 and unplug the wastegate...see how high it goes!

Ok, don't do this. You could try some sort of electronic boost controller that'd try harder to keep boost high all the way to redline.

Re: Boost fade
 

A T28 is more than capable of holding 18psi to 7000 RPM. Do you have a major restriction on your intake track? Really dirty air filter? Stock IC piping? Stock BOV? When doing the boost-leak test, how high have you tested it to?

BTW, unless you have a FMIC on your car you should not be running that much boost on pump gas, especially untuned. Do you have the fuel to support it (pump, injectors, etc.)?

Re: Boost fade
 

List all of your mods please.

Re: Boost fade
 

Look at your complete intake & intercooler system and look for a restriction. What are the measurements of your frontmount?

The reason I say this is because a friend of mine bought my old turbo set-up from me and installed it on his 1g (2.0 w/2g pistons, Comp cams). Made good pump gas power at 18 psi until around 6500rpm, kept loosing power quickly after that. Since I was doing the tuning for him with DSMLink over the internet, I couldn't see his set-up. Fuel was good, 18 psi at the intake all the way to 7500rpm. We kept trying to figure out where the power was going for the longest time. I knew he had a front mount, but I couldn't remember what size. Finally I got him to put a boost gauge on each side of the front mount and make some runs. He found at 18 psi at the intake manifold he had a 1.5-2.0 psi restriction at the intercooler. Meaning his turbo was pumping more boost to keep the intake psi up. No need to look any further. Another front mount is on the way.

Re: Boost fade
 

but most good front mounts are semi restrictive. the air has to bump into something to transfer the heat.

Re: Boost fade
 

what about upgrading the wastegate actuator spring
here the link to Forced Performance website and the page where you will find the info and parts
http://linux.forcedperformance.net/m...egory_Code=DSM

Re: Boost fade
 

^ If multiple boost controllers aren't working that probably won't help (unless their is something wrong with his current wastegate).

Re: Boost fade
 

I dont think the t-28's come with the upgraded wastegate actuator though.So why would that not be it, did you read what it said. Describes his situation to a T

Re: Boost fade
 

I doubt his flapper is being forced open by exhaust preasure at only 18 psi with a 3" exhaust. Its possible I suppose, worth a shot if all else fails.

Re: Boost fade
 

But not that restrictive. ;)

Re: Boost fade
 

Most side to side FMIC will produce 1-2 psi pressure drop. The turbo spits out hot air then you cool that air off and it becomes more dense, thus would have less pressure, or atleast thats my take on it.

~John

Re: Boost fade
 

Alright, here is a more complete list of mods:

crushed 1g BOV (didn't leak up to 20 lbs in my tests, i went to 25 lbs could only hear the BOV hissing)
650 injectors
190 walbro fuel pump
Greddy 24R FMIC kit and the few pipes it comes with to hook up to stock piping
Dejon intake and upper intercooler pipes (2.25" I think)
Ractive (?) air filter
17 lb actuator from FP, not the 11lb it came with. I thought this was the issue originally and it didn't help much.

Relevant Stock parts:

lower intercooler braided hose
braided hose from BOV to TB elbow

Re: Boost fade
 

Get a real K&N or AFE air filter, those cheap generic cotton-gauze filters have been proven to flow much less than the quality brand name ones.

Re: Boost fade
 

I always wondered if this was a big deal or not. The previous owner had it on there and I never got around to changing it, even after it fell apart and I had to glue it together again. Haha, I'll let you know if this helps in a week or two or whenever the filter arrives and gets installed.

Re: Boost fade
 

Not only do they flow less, but depending on the amount of air you are trying to pull throught a filter, you can cause it to collapse and potentially fall apart, especially with those piece of shit off-brand filters.

Re: Boost fade
 

Or the big HK$ foam things that always end up in the turbo. I would look at your boost controller and how its routed.

~John

Re: Boost fade
 

Here's what I did: took off the filter, cleaned it, ran a few passes WITHOUT the filter on, same thing happened. Faded to just under 15 lbs by 6500 rpm.

Maybe my wastegate sucks.

Re: Boost fade
 

I did more tests the other day, here is what I've gathered:

boost controller was hooked up to turbo as pressure source, probably 12" of hose to turbo and 12" to wastegate.

I changed the pressure source to be the intake manifold, didn't help.

I lowered the boost one full turn on the controller. Nothing really changed except it made 17lbs and faded to 14. Weird.

I upped the boost two full turns, it made uncontrollable boost, instantly went to 25 lbs so I let off completely. Then I did a pull and controlled the throttle so it made 18 lbs, maybe 50% or 60% throttle, held solid to over 7k rpms.

The HZ on the AFC read something like 2400, I usually max out around 1700. This makes sense though (I think) because with the throttle body partially open, there would have been higher pressure in the pipes than the intake manifold, and the ssqv bov opened because I heard a high pitch airy sound past 5k rpms. So it was measuring more air than was getting to my engine, which is why it was so high probably.

Then I put it back to 1/8 turn over the original value, now it spikes to 19psi, then fades to 15 or 16.

So to me it seems like the boost is coming on too quickly and the boost controller can't keep it under control, takes 2k rpm to settle to where it should be. Could this be a wastegate problem?

Re: Boost fade
 

Sounds to me like your MBC should be set somewhere between where it started and the two full turns. What happens with just one turn up? Did you route the MBC back to how it was before (turbo-MBC-WG)? That routing will help control spike.