The Dreaded Diverter Valve (DV) - What's actually happening to your boost

[vag-tech]

This may be of interest to some of you guys, to get some insight as to what's actually happening when a DV goes bad and exactly what this does to your boost.

This example is taken from an Audi A3 2.0 TDI 8P3 (stock map) we had in today displaying a classic under-boost fault.

When a car comes to us displaying these symptoms one of the first things we do is carry out a road test while monitoring a few key values. You can see in the attached image (Fig.1.) that the engine ECM is wanting to see ~2.4 bar peak boost (green channel) and the actual, achieved boost is ~2.0 bar (red channel), confirming under-boost condition...resulting in poor performance etc, etc.
After checking the DV function, we confirmed another DV faulty (as many of you will know, the diaphragm that fights the applied controlled vacuum to regulate boost had a leak, preventing your car from boosting to specification).

After fitting a new DV you can see from the values obtained during the road test following repair (Fig.2) that the actual boost (red channel) pretty much traces the desired boost (green channel), recapturing the our 400 mbar of lost boost and getting our performance back!

FYI:

• Blue channel is accelerator pedal position so you can see exactly when maximum driver demand is applied and how boost responds.
• Purple channel is duty control to the vacuum solenoid i.e. low = give me max boost

Hope this was helpful

 

[S11M]

Very interesting. Thanks for that. Which diverter valve would you recommend? Rev G or Rev D or GFB?

 

[HHS3]

Great post vag-tech.

Very interesting. Thanks for that. Which diverter valve would you recommend? Rev G or Rev D or GFB?

I'd personally recommend the GFB DV+ over any other diverter valve.

I picked up my S3 last year which had the Rev C in it, got my car remapped in March and had the Rev G put on at the same time which was noticeably better. Several tuners including R-Tech state that the Rev G DV is better then the Rev D. This is because even though the Rev D has a piston design, rather than the
the diaphragm from the Rev G, it doesn't hold boost as well compared to the latter. The downfall to the diaphragm design in the Rev G is that it is prone to rupturing when driven hard over a period of time, especially in remapped cars, so it is to be treated as a service item.

I had the GFB DV+ fitted a couple weeks ago when I had the pre-cat delete done in preparation for stage 2 next month, it is clearly superior to the Rev G in that it simply holds boost for longer. It's made out of metal as well so it wont split and with the revised design back in 2013/14, you won't ever need to replace it. Here's some more info on it: http://www.amdtuning.com/blog-section/blogart3201

 

[vag-tech]

When it comes to boost, and life generally, I will always be a fan of non-perishable over-engineering