Vacuum reservoir for wastegate actuator control solenoid OM606
 

In an attempt to improve the boost response between shifts, I fitted a small plastic fuel filter (w123 plastic pre-filter) inline on the vacuum feed line going to the solenoid that controls vacuum feed to the wastegate actuator. I put it as close to the solenoid as possible. The idea is that the small filter acts like a vacuum reservoir so that when the solenoid opens up there is abundant vacuum standing by to close the wastegate quickly. Without the reservoir, the volume of vacuum needed to close the wastegate is limited by the small and long white plastic vacuum feed line coming from the brake booster. It “feels” more responsive, but I need to do more test taking it off and on, driving around, to see if it’s just my imagination. I’ve only driven it a mile to starbucks and back at this point. If anyone out there has a boost gauge installed maybe they can try it to see if the gauge provides more useful data. The feed line is the small white plastic line going to the top of the solenoid located under the MAF sensor, by the air filter box.

This is a very good idea! I was messing around the other day and just connected the wastegate straight to the vacuum sounce. It was all around more responsive but of course, it eventually set a code and it's also boosting a little higher than normal but not too bad.

One improvment I would suggest is to put a pinhole oriface in the upstream connector to slow the venting of vacuum when the solenoid dumps. As an alternative you can put a much larger reservoir to ensure enough volume. Connecting a vacuum gauge to the wastegate will be more telling if you have the proper size.

the TDIs from VW and Audi use a 3" diameter ball as reservoir just before the solenoids for the VTG control. A huge direct connection to the vac source will influence brake and the other vac things.
Alternatively also check out for 123 central locking reservoir.

Tom

Hi Mundoracer, is this what you've done? The reservoir might be too small?
I haven't properly tried it yet.
Something different:
how about moving the solenoid as close as possible from the waste gate? There might be less lag as the pipe would be shorter, or no use doing so?
cheers.
Olivier

Mundoracer, Can you post an update on your Vacuum boost mod? I am curious if you still notice a difference with this on vs without (normal)

This is a pretty simple non invasive mod, I will definitely give it a go myself, if you have any luck.
98 E300TD

Agreed! Please post an update.

I tried this and I can tell you what happens. I started with a small chamber and increased size up to about 100cc. It does, in fact, smooth the shift dip but the down side is that a chamber large enough to smooth the boost response will also trigger a code because the ECU tries to reduce boost at cruise. Since the volume of the chamber slows down boost changes, the ECU thinks the wastegate isn't responding to the command to reduce boost.

Thanks for the info KarTek. Do you still have the reservoir connected? I don't really think it is worth it for me to put this on since it will throw codes. Having errors come up on my display is too annoying for me.

I took it off. I could never strike a balance between a large enough volume to effectively dampen the boost reduction but not so much that it set a code.