Hi everyone.

I am having an issue where I am losing boost on my 2001 A4 1.8T Quattro.
It has always had plenty of get up and go, but it abruptly started feeling like my '95 Jetta 2.0 accelerated faster.

I did the usual visual checks all along the turbo outlet all the way to the TB, plus all other hoses I could find.
I made sure the wastegate shaft moved freely by hand.
I tested the coil resistance of the wastegate actuator solenoid.

So, today I rigged up a boost gauge to see what I was actually getting.
Upon acceleration, I get boost (~6-7 psi), but right before 4K, the needle drops back down towards zero.
This is where I should start to feel the "pull" of the turbo, but it isn't there.

It does this every gear, but is more noticeable 1st through 3rd.
4th and 5th are closer to being under the 4K mark, so it isn't as noticeable.

Another notable thing is that the secondary air injection pump seems to be running in accordance to where the boost *should* be.
As I push the gas harder, the SAIP whines louder, but there is no boost to complement it.

Here are a couple videos showing what I am trying to describe:

Accelerating down a straight stretch of country road.
Watch the boost needle the first 10 seconds...this is where it is most pronounced.



Climbing a short hill.
You can hear the SAIP whine well in this clip.


The only mods on the car are a turbo-back Stainless exhaust, a 12 lb steel LWFW, and a 240mm S4 clutch/PP.

Any ideas??
Any help is appreciated!

:Edit: I saw as I was posting the ideos on youtube that boost leaks can be found using an air compressor and a regulator to pressurize the system.
I should have though of this, seeing as that is how I test pressure vessels after I weld them... .
Maybe I'll have to try it if I can scrounge parts together to do it.

 

Yes, you should start with the simple steps of a boost leak test and scanning for codes.

A side note, it's recommended to get a boost/vac gauge instead of just a boost gauge, if you have large boost leak it would be noticeable at idle on the vacuum side of things.

 

Hi BaseDrifter.
Thanks for the response.

I plan on trying to pressure test it today, depending on parts I find to do it.
That gauge is what I had for now.

A question that came up in my mind is: what are the normal boost and vacuum readings for a stock 1.8T?
I didn't have the gauge when it was running correctly, therefore I have nothing to compare to.

Thanks again!

 

You should see 9psi tapering down to 5-6 as you get high in the revs, and at idle you'll see -18 to -22 vacuum. Higher than that (-16 or higher) and you have a definite vacuum leak.

 

That's not your SAI pump, it only runs at idle on cold starts.

Sounds to me like the "dentist drill" noise indicative of a blown turbo. This video is from an S4 but the sound is the same:


I have a boost leak tester I would be happy to loan you if you promise not to steal it

 

Okay, so I made a pressure tester out of a 2" pvc pipe cap with an air fitting tapped into it. That was put into the TIP where the MAF was attached.
I removed the "Hockey Puck" going to the breather system and plugged the hole.
I applied up to 20 psi, and I didn't find any obvious leaks...The oil pan was gurgling, but research seems to indicate that is normal.

I did find that there is a rubber tee at the rear of the valve cover that goes between the valve cover breather, a pipe coming from the turbo area, and somewhere behind the engine that was all limp and squishy. It did have a small hole in it. I will be replacing that.

Ok, 9psi with it tapering down at high revs... what is considered high revs?
I never saw higher than 7psi, believe.

I had assumed that that whining was the SAIP...
I just rebuilt that turbo with a good quality (Melett) turbo rebuild kit...maybe 1000 miles ago.
Maybe I didn't line the turbine and the compressor impeller up as perfect as I thought and it was out of balance?
What causes the "dentist drill" noise and would that cause a loss of boost like I am experiencing?
I guess I'll have to pull the TIP and check the impeller shaft play when I get a chance...

CCA4, is your boost leak tester and different/efficient than what I had done for my testing?
And of course I wouldn't steal it.

I really appreciate everyone's input. Thanks!

 

Nope, that's exactly what mine is. A lot of people can't (refuse to) figure it out so I thought I'd offer. Sounds like that test was done properly and with good results, so I'd cross a boost leak off your list.

lol thanks!

The stock turbo is quite small and moves out of its efficiency range above about 5500rpm. Anything above that and it can't move enough air fast enough to make more HP than it does at lower RPM's.

Bad SAI pump wasn't a bad guess, the noise in your videos is almost identical to the noise that a bad SAI pump makes. There are two important keys that made me say bad turbo. First is that the frequency of the noise in your video changes with engine RPM. This wouldn't be the case with a bad SAI pump, as it's not controlled directly by the RPM of the engine. The second is that everything was up to operating temp when you took the videos. Your SAI pump only runs on cold starts for 30seconds to 1 minute. It's purpose is to help warm up your catalyst faster before the engine reaches operating temp. This extends the life of the cat (which is expensive as ****) and improves cold start emissions (which is good if you're into that sort of thing).

As you mentioned, I would pop the turbo inlet off and check shaft play both laterally and axially. Also check the inside of the compressor housing inlet for scratches. If the compressor blades are making contact with the inside of the housing, you could be setting yourself up for some catastrophic damage. The dentist drill noise is caused by metal-on-metal contact without properly sealed and lubricated parts. Could be the bearings that the CHRA rotates on or the compressor/turbine fins contacting their respective housings. It's hard to say without tearing everything apart. Have you seen any blue/white smoke from your exhaust? That would be another indicator.

 

So, I finally got a chance to go out in my shop and do some diagnosis.
I pulled the TIP off and checked the shaft play... no shaft play in/ou and a tiny bit up/down, but barely noticeable.
I then got a mirror and flashlight down there, and this is what I found....






Just for comparison, here is a pic of another K03 with fairly intact compressor fins...



WTF?!? So that's where the boost went!
I see the case of the dentist drill sound.
I can't see what caused this..
There wasn't anything foreign in the piping.
There is hardly any play, and I can't see play causing this anyway. Play would bend the tips of the fins...not wipe them out completely ...
Oh yea, there's no smoke out of the exauust.
Any ideas?

I suppose I need a new turbo now...
Any suggestions?
This is my travelling car, so I had planned on not modding it too much.
I wanted to keep it reliable.
I considered upgrading the turbo to something bigger, but then I would need a tune, then injectors, etc... which makes me wonder about reliability on trips.
I am new to the whole turbo scene, so please bear with me.
I can hold my own on most other automotive diagnostics, but this new territory for me.

Thanks for everyone's advice and information.
I am learning alot.

 

Well there's your problem! LOL

Looks like it tried to eat itself. I can't imagine what would cause that, that's wild lookin. I've never seen that before...

If you're looking for a reasonably priced upgrade, give Slappy a call at Frankenturbo. It's a K04 hybrid that you could run on stock tune/fueling, then upgrade later as needed. Your other option would be to pick up a used K03 in the classifieds, then rebuild it. By far the cheapest option.

 

Yea, I had already been eyeing up a Frankenturbo..
However, the $1144 (w/ shipping) price tag is kinda the clincher.
I normally have no problem buying toys, but I am going through a divorce at the moment, so cash flow can be iffy.

I will have to see if I could afford the FT.
Is it worth it?

If not, yea, I'm going to have to find a K03 to rebuild.
I didn't see any in the classifieds...anyone know of any for sale?

Thanks for all of the help! I love to learn and this has been another educational experience.