Possible Boost Problems.. any ideas ??

[MR-GTI]

Hi all,

Just a quick question, hoping someone can shed some light..

I have just got my car back from the 30k service. Car seems to be going fine , but I noticed today that when I give it a gut full it comes on boost then drops off, then comes back on. Now I'm not decelerating, I still have my foot in it.
It is very noticeable in 2nd gear.
I can actually have my foot down and it will keep revving and i feel it boosting then it drops off and back on again.


The car is stock except the K&N and disconnection of the BOV. I put everything back to stock before I took it for the service.
Now all I have done is put the Pod back on. I have also checked that the BOV Vac line is connected properly.
Nothing else has been touched, and it is now even more noticeable as you can hear it more through the pod..

Any ideas.

Regs MR-GTI

[h100vw]

Reconnect the DV, it needs that. If it still surges then you could be experiencing the inlet pipe collapsing and then opening up again. Intermittently chocking the engine.

Gavin

[MR-GTI]

The DV is connected.. it semed to be fine till I put everything back to standard.
Just a little baffeling to me....

Thanks.

[h100vw]

You would need VAG-COM to verify my theory, you would see the airflow going up and down.

Are you sure the DV is good? Is it a std VW one?

Gavin

[MR-GTI]

Yes it is the standard one, as mentioned earlier everything is stock. All I did about 20,000ks ago was add a K&N Pod and disconnect the DV to allow for more sound flutter. I have not had a problem at all.

It was due for service so I just put the standard air box back in and re connected the DV which is 1 single Vacc hose. Nothing to it.

When I drove it the dealership I just cruised due to traffic so I could not tell if it was doing it.
Once I picked up the car from the dealership and drove it home I noticed it but ignored it as I though that I was imagining it.

Today I drove it and went from a small run and noticed it. I then came home put the Pod on checked the DV hose and did nothing else and it still does it, it's just more noticeable due to the Pod.

mmmmmm.. Got me stuffed..

Thanks .

REgs MR-GTI

[JCM308]

Silly question but is the DV put back on the right way?

[MR-GTI]

Not a stupid question at all, but fortunately it is the right wau I never took it off.

To disconnect the DV/ BOV all you do is pull the Vacc hose off it add a BLOCK OFF hose to the DV and then block off the original hose that was going to the DV, this way there are no leaks and everything except the DV is working normally.

Regs MR-GTI

[JCM308]

No probs. It's got me stuffed then. I think you may have to use h100vw's idea and get the car checked with Vagcom.

There is also a possibility that you have dirty fuel (or even water in it). I haven't experienced this in my polo but I did in my S13. Had similar characteristics to what you're describing.

[MR-GTI]

Yes got me stuffed as well... Fuel is always from the same servo, but could be possible, just seems all too funny that before the service it was all good and now it's not... It's just a real bitch to get back to the dealership thas all.
Blood time wasting ...

I'll take it for another run tonight and see if anything has changed.

Thanks again.

Regs MR-GTI

[Blitzen]

I had a very similar problem when I was running my Forge BOV...It was revving, but producing little to no boost. I would stop and restart the car, and the problem would go away, but it would invariably come back at some stage, and was starting to happen more often.
After my accident, I felt that my car was running a bit sluggish, and very laggy, and put this down to heat soak, but I then realised it was happening when cold. I had it scanned for codes, and found that it had these codes...:
- 17705 - Pressure drop between turbo and throttle body(check DV)...Intermittent.
- 16795 - Secondary Air Injection System: Incorrect flow detected...Intermittent.

After these codes were cleared, the car ran like a dream, and I was very happy. I was told it was running very laggy as this may have been some sort of semi limp mode.
I have since gone back to the stock DV, and never had any dramas.
The second code is associated with the air pump, which is at the front of the engine(the 2 black 20mm diameter hoses, one from the airbox to the pump, and then from the pump to the valve at the top of the engine).
You may have thrown a code associated with not running the DV. Get the codes cleared and see how it goes.

[MR-GTI]

mmmmm interesting.. I have added a small filter to that hose that runs to the air box when i run the pod... and maybe that and running no DV has thrown a code.

All too weired for me , I might just try take the car back and see what they think.

Thanks again.

[Spec83]

That flutter is the air bouncing back and forward between the impeller wheel and the throttle body. This places a fair ammount of extra load on the turbo bearings / shaft (as ir almost forces the turbo to spin backwards) plus increases lag as the turbo slows to less RPM and takes longer to speed back up again

Just leave the stock DV on and forget about the wanky noise!!!!

[mozzzy_2000]

That flutter is the air bouncing back and forward between the impeller wheel and the throttle body. This places a fair ammount of extra load on the turbo bearings / shaft (as ir almost forces the turbo to spin backwards) plus increases lag as the turbo slows to less RPM and takes longer to speed back up again

Just leave the stock DV on and forget about the wanky noise!!!!

Yeah I was going to say what you are discribing is either turbo flutter or surging and the DV is actually meant to prevent it. I've just recently installed the APR R1 DV and the increase in performance over the stock DV is immense. Whilst my stock bosch DV was in perfect condition it is clear that its performance is sub par. The APR DV holds the boost far better through the gears and almost eliminates the turbo lag behind gear shifts and this has an overall effect of faster acceleration. It is very noticable.

[Kai]

That flutter is the air bouncing back and forward between the impeller wheel and the throttle body. This places a fair ammount of extra load on the turbo bearings / shaft (as ir almost forces the turbo to spin backwards) plus increases lag as the turbo slows to less RPM and takes longer to speed back up again

Just leave the stock DV on and forget about the wanky noise!!!!

I wrote a large reply out to this. But deleted it. i cant be arsed. All i can say is learn how a turbo works. Thanks.

[MR-GTI]

Boys Boys boys..

I think a few of you have miss diagnosed the problem and are going off in another direction..

For the sake of not causing an argument I will give you some back ground.
I have been playing with cars for over 20yrs.
I know how a Turbo works and I know how and why flutter is created.
So I'm not ignorant..nor am I an inexperienced child..

The flutter has nothing to do with it..it will not stop the car from boosting and definitely will not make it drop off.

This is an uncomplicated issue... so one more time for the Dummies !!
The engine drops on and off boost when up in the rev range..
It was not there before never has been regardless of adding the Pod ect..but it is there now.. It has nothing to do with using a Pod filter or blocking off the DV..
Sure I agree maybe by blocking off the DV it might has played havoc with the air flow and sensors.. that's why I'm asking..
I'm thinking it might be possible that one of the mechanics that just serviced it might have accidentally disconnected or unplugged a vac line..

I have played and built many cars over the years, some being turboed, I have raced and owned cars that have run sub 11sec quarters.. so I would like to think I have more than 1/2 an idea about cars and their workings

I'll admit I'm not up to scratch with the new technology as I'm from the OLDSKOOL Blow Through and Suck through Turbo set ups, with carbies and simply fuel injection set ups..So yes I will admit I do not know everything...

All I'm saying is it is very easy to judge someone when you don't know the history or the facts, and I do not hold that again anyone.

So thank you all for you input and advice. I will sort this out and let those who don't think that I'm a 16yr old playing with a High tech cars, know the result.

Thanks.

Regs MR-GTI