Overboost - naughty remap?

[volvic]

found some cool pics! borrowed from team- bhp.com

Variable Turbine Geometry technology is the next generation in turbocharger technology where the turbo uses variable vanes to control flow against the turbine blades. See, the problem with the turbocharger that we’ve all come to know and love is that big turbos do not work well at slow engine speeds, while small turbos are fast to spool but run out of steam pretty quick. So how do VTG turbos solve this problem?

A Variable Turbine Geometry turbocharger is also known as a variable geometry turbocharger (VGT), or a Variable Nozzle Turbine (VNT). A turbocharger equipped with Variable Turbine Geometry has little movable vanes which can direct exhaust flow onto the turbine blades. The vane angles are adjusted via an actuator. The angle of the vanes vary throughout the engine RPM range to optimize turbine behaviour.

In the 3D illustration above, you can see the vanes in a angle which is almost closed. I have highlighted the variable vanes so you know which is which. This position is optimized for low engine RPM speeds, pre-boost.

In this cut-through diagram, you can see the direction of exhaust flow when the variable vanes are in an almost closed angle. The narrow passage of which the exhaust gas has to flow through accelerates the exhaust gas towards the turbine blades, making them spin faster. The angle of the vanes also directs the to hit the blades at the proper angle.

Above are how the VGT vanes look like when they are open. I’ve not highlighted where the vanes are in this image since you already know where they are, as to not spoil the mechanical beauty that it is

This cut-through diagram shows the exhaust gas flow when the variable turbine vanes are fully open. The high exhaust flow at high engine speeds are fully directed onto the turbine blades by the variable vanes.


Variable Turbine Geometry has been used extensively in turbodiesel engines since the 1990s, but it has never been on a production petrol turbocharged car before until the new Type 997 Porsche 911 Turbo. This is because exhaust gases are alot hotter than diesel engine exhaust gas, so generally the material used to make VTG turbos could not stand this heat. The 997 911 Turbo uses a BorgWarner VTG turbocharger which uses special materials derived from aerospace technology, hence solving the temperature problem.
I hope I have helped you understand how VTG works.

 

[Muttley]

found some cool pics! borrowed from team- bhp.com

GREAT photo's, best description of VNT I've seen. I'll just copy that for future reference . . .

 

[glynnd]

Edited for accuracy.


It does sound like a sticky vanes issue and it is a nasty/messy job. I think Glynn may have cleaned his himself before the hybrid went in (correct me if I'm wrong - I know someone did not that many months ago).

In the end it is an issue for the garage to sort out.

The map is a possibility as it could have been butchered by someone. However on a law of averages it is very unlikely.

Fortunately the garage is playing ball and hopefully you'll get your car back soon in order.

I did clean mine, though tbh I had no issues at all with sticky vanes, prevention better than cure?
Glynn

 

[Swig]

Thanks volvic for the pictures and explanation. A nice piece of engineering.

I've exchanged a few emails with a tuner in Chesterfield who'd put the old SEAT map back in the car for about 30 quid. Nice and cheap for that but as said above this may not be the problem!

They said they don't clean VNT turbos preferring to exchange them for a new unit. Don't know whether that's because they have reservations about it's effectiveness or just would prefer the extra work. Anyone views on that?

The instructions for the cleaner don't look to tricky for any competent mechanic to follow (pretty easy to get to if you google "innotech turbo cleaner" and follow the top link to the mk4 golf forum - I'm too much of a newbie to be allowed to post a link directly)

 

[glynnd]

Access to the turbo is not the easiest but the job is straight forward. Hardest part is unbolting the downpipe from the turbo. To a degree the innotech stuff does work, but these vnt mechanisms need working often to keep them free. I would say town drivers and granny and grandad impersonators suffer most. I never had an issue with my turbo till it failed at 133k and that was due to the agressive map! If you want somebody to do it;
DSB Autocare nottm just off junction 26 ask for Dave he has done quite a few! mine included and he is a top bloke 20 years working on vw group stuff.
Glynn

 

[Husbandofstinky]

Glynnd would be a good starting as he's done it (confirmed).

I'm not surprised they wanted to sell you a unit, its just the way of the world today. Old school would be to get it off and clean it. That would be my first port of call before installing a stock map, liasing with Glynn in the process for guidance if he was happy with it.

Where there is a number of possibilities for a problem, the old golden rule of doing the least expensive/least time consuming items first holds fast. If it were me then clean turbo, stock map (although I don't think its the issue - but could be), then replace turbo - as a very last resort. I would probably explore other avenues first before the last item - just in case.

As said previously garage should sort it.

 

[Husbandofstinky]

Some members have also mentioned in the past of the old Italian tune up to help clear the blades. It supposedly helps to cook the crap of them. Personally I'm not too keen on the idea but it might help. It would be a case of warm up to operating temp, heat the turbo up (give the car some wellie), limp mode, on and off and start the whole process over again. Continue until you give up on it as I can't see it curing the problem, but its got to be worth a try due to cost and effort.

Lastly, although this is nothing related, an ECU reset might be worth while as it may have not been done for a long time. This is something I do every six months and rebases the ECU and its free. Just disconnect your battery for 20 mins - don't forget your radio codes though.

 

[Swig]

Thanks - I'll try and find those codes before disconnecting anything.
I'm not too keen on ragging the crap out of a car that might have something wrong with it either!

 

[glynnd]

Its got to b e diconnected for at least 30 minutes stinky!
Glynn

 

[Husbandofstinky]

No worries Glynn, I always do mine over night. However I'm sure someone's said 20 minutes is enough. Overnight is more than plenty.

 

[TornadoRed]

The mechanic at the dealer is prepared to try and turn down the boost at the actuator - is this a good way to go. They don't have the facility to change the ECU map themselves.

This is something that should only be tackled by someone who has the right experience.

When I had an upgraded turbo installed, it took my mechanic several tries to get the actuator just right: put it on the hoist, make an adjustment, take it for a test drive and get VAG-COM logs, put it on the hoist, make an adjustment, take it for a test drive and get VAG-COM logs, and repeat. It would have been MUCH simpler and quicker if a dynamometer had been available. He also installed a boost valve, just as insurance.

With an incorrect adjustment, the turbo will underboost or overboost, both are bad.

 

[Swig]

Yes. Some people here saying that there's no adjustment on the turbo I've got anyway! It's just that anywhere else it would probably be me paying the bill.

Your car's done an impressive mileage! Still going strong?

 

[TornadoRed]

Yes. Some people here saying that there's no adjustment on the turbo I've got anyway! It's just that anywhere else it would probably be me paying the bill.

Your car's done an impressive mileage! Still going strong?

The ones who say there is no adjustment are probably people who should not try to make adjustments. The actual lengthening or shortening of the actuator rod is quite simple but also quite tricky. Someone who installs turbos for a living would be the guy to see.

My Golf is ready for its next 300k miles or more. A few dings and scratches, but it runs better than new... I think about 60% more HP and 60% more torque than when new. I must do something to improve cornering next.

 

[Swig]

My mk2 golf died after 160k miles. It had had one engine and one gearbox rebuild. Another gearbox rebuild loomed.

Am I right in thinking that it adjusting the actuator rod would have been unlikely when it was remapped?

 

[TornadoRed]

My mk2 golf died after 160k miles. It had had one engine and one gearbox rebuild. Another gearbox rebuild loomed.

Am I right in thinking that it adjusting the actuator rod would have been unlikely when it was remapped?

Remapping is a software change, adjusting the actuator is mechanical. The people who know how to do the one thing do not know about the other.