Exercising the Turbo "vanes"

[asthpsw]

I expect most have experience or at least read about it.........that the vanes in a VNT Turbo with time gets sooted up & thus the movement is restricted or made more difficult.

I did for a period of time under hard acceleration, up a hill on a motorway get the engine to go into limp mode once you lifted your foot off the accelerator to change to the next gear.................this tended to happen at about 2800 revs & above. (Excessive boost pressure was the error code & what put it into limp mode.......this is because the vanes pitch do not return to normal setting quick enough & hence overboost)

I got the car out of this habit by lubricating the Turbo linkages with WD40 (idea got from this forum 12 months ago ?)..................& also doing the hard acceleration as described above often so that hopefully it cleared the soot gradually from the Vane movement area.........I say gradually because it of course for awhile kept going into Limp mode, then reset it, try again, limp mode etc etc........but it worked.

I'd now like to keep it from getting the state above.............so what is the best way of getting the vanes to go through the maximum movement ?...ie get the "pitch" at its max ?

Is it best in the highest gear possible ?..........foot hard down ?......ie does this open the vanes to its full pitch ??? If not how best to do ?

Engine is a 110bhp (non PD)

Paul

 

[muddyboots]

I'd have thought the best way would be to regularly accelerate fully then lift off, keep doing this a few times should exercise them.

Or failing that, run the self test in vag-com which cycles them every few seconds...

 

[asthpsw]

Thanks but accelerate under what conditions, would accelerating on a flat road & in a low gear open up the vanes to the full amount.....ie I'm not sure day to day accelerating would really clear them otherwise they would of not got sticky (sooty) in the first place.

Paul

 

[stoneyfordNI]

id say 4th 5th 6th , get it under full load , have you a boost gauge , as soon as u feel or see full boost , back off drop the revs and go again ,

 

[dmjw01]

Full boost does not necessarily correspond to the vanes being fully "open". Somewhere above about 2500 to 3000 rpm, I doubt the vanes are ever fully open, even when the turbo is on full boost. If the vanes did open fully at that speed, you'd get overboost. My suspicion is that by the mid-2000s rpm the vanes are already partially closed, so you need to start a bit lower.

A good way to be absolutely sure of cycling the vanes through their full travel is to use VAG-COM, put it in group 11 and click "basic settings". This puts it into an automatic self-test mode where the engine fast-idles at about 1400 rpm and cycles the vanes through their full travel. (The fast idle speed is presumably to avoid a compressor stall when the vanes open fully.)

Incidentally, I find my engine really enjoys being put under sustained load. Unfortunately I'm just a 10-stone weakling and no matter how hard I drive the car it doesn't really seem to load the engine enough - it accelerates so quickly that I can't sustain the load for long periods. But whenever I have a couple of decent size passengers on board and go for a long, fast drive, I find the engine drives absolutely beautifully afterwards, and the effect is much better than VAG-COM. I'm considering buying a few big bags of ballast! Or maybe I should put an ad in the lonely hearts column.... "Single man, OHAC, seeks fat lass for fun, friendship and long-term turbo maintenance."

 

[craig-pd130]

What David said above.

I usually give mine a VNT cycle / soot clearout on main roads by opening up from about 1600 rpm in 4th or 5th (depending on road conditions), and holding at full throttle until just before 4.5K.

The higher the gear, the more time you get in the "VNT zone" while accelerating. Providing you're progressive with the throttle (i.e. smoothly opening it over a couple of seconds rather than mashing it) you won't put the engine under excess loading.

 

[cheshire cat]

I think this exercising is turning into an urban myth, I don't doubt that vanes will stick given time and too much grannying but they are normally "open" if that's the word we are using, at rest, ie: engine off. On start up they should travel full to closed (under vac) and then start to "open" as revs rise and will be petty mutch there by 3K. Generating high boost is greatly exagerated on inclines and dependant on any mods or even all parts working correctly, maybe you just need a pressure guage and boost valve

 

[Sisson]

^^^^ boost valve???

do you mean a boost gauge, to monitor the Boost being produced???

 

[cheshire cat]

should really be called a boost control valve, it will remove spikes and hopefully increase an otherwise shortened tubo life

 

[craig-pd130]

I thought the vanes defaulted to minimum boost when no vac / engine off, as a failsafe, and only opened to give higher boost under vac?

 

[stoneyfordNI]

correctamundo!!!!!

 

[asthpsw]

Exactly, thats what I thought.....................so we are back to square one what is the best way of getting them opening fully up ?

I can see what as been said previously that High gear, from about 1500 revs open her up slowly & gently to full accelarator position....but in view of anyone what is max RPM that there isn't any point in exceeding ?

Paul

 

[stoneyfordNI]

surely where peak torque is developed as after that boost starts to fall back.????

 

[dmjw01]

My suspicion, based on sticking my head out the window and listening, is that the vanes are already on their way back down by about 2500 rpm, possibly earlier.

Having said that, mine seems to benefit from a few full-throttle runs going all the way up to 4500+.

I suspect there's more than one thing going on. Moving the vanes is good, but I wonder if you also need to get the EGT (exhaust gas temperature) up to remove some of the carbon - maybe this is why the engine benefits from going all the way up the rev range? Dunno, I'm guessing...

There's no doubt that mine drives especially nicely after I've given it 5 minutes moving the vanes with VAG-COM, and then do some full-throttle runs along a nice quiet bit of dual carriageway - particularly if it's had a few days of getting stuck in traffic jams on the way to work. Or just fill the car up with pie-eaters and go for a long drive. Either works well.

 

[cheshire cat]

I thought the vanes defaulted to minimum boost when no vac / engine off, as a failsafe, and only opened to give higher boost under vac?

first part ---Yes: depends on the word open, max vac is at idle then proceeds to reduce as revs rise, end of travel (on mine) is approx3krpm when there is a small amount of vac left in the system,

 

[cheshire cat]

I suspect there's more than one thing going on. Moving the vanes is good, but I wonder if you also need to get the EGT (exhaust gas temperature) up to remove some of the carbon - maybe this is why the engine benefits from going all the way up the rev range? Dunno, I'm guessing...

)

I think there's alot in that!!

 

[Muttley]

The variable geometry vanes in the exhaust turbine are positioned by the ECU. They are actuated by vacuum, but it is modulated by the N75 valve. They are spring-loaded to be fully open i.e. lowest boost, when the engine is off. When the engine starts the ECU sets them to the narrowest opening, so they are moved from one stop to the other every time the engine starts.

There is a vacuum pump on the engine to ensure that there is always sufficient vacuum to operate the ancilliaries: brakes, EGR valve, turbo and manifold flap.

The narrower vane openings give an increase in gas speed into the turbine at low exhaust gas flow i.e. low revs. This spins the turbine faster and gives increased boost at low revs compared to a fixed-geometry compressor. Opening the vanes as the engine revs and exhaust gas flow rises keeps the compressor spinning at its design speed and delivers a constant, maximum, boost from low revs (1500) to max revs (4000 - 4500).

The vanes are in the exhaust gas flow, so get soot deposited on them. A diesel engine produces soot in three areas of the performance diagram: on cold start (poor mixing, cold spots), at maximum revs (the smoke limit, added fuel is not completely burned) and when the EGR system is active, at part-throttle (EGR reduces combustion temperatures to inhibit NOx formation, by reducing oxygen content, so increasing soot and CO prodution).

The best thing you can do to reduce sooting-up of the vanes is to reduce the EGR activity, either by using VAG-Com to set the EGR to minimum or by blocking the EGR valve's activity (putting a blanking plate in the recirculation pipe, pulling off and sealing the vacuum line to the EGR valve or disconnecting the electrical connector to the N18 valve).

The soot can be burned off by getting the turbo hot and keeping it hot. This means load at high rpm - climbing a steep hill fast, say on a motorway or dual carriageway.

Exercising the vanes is a different matter. The ECU tries to keep the turbine spinning at best speed, no matter what the gas flow being generated by the engine exhaust. So at low revs, the vanes are closed down to a minimum opening, causing the gas speed to rise and spin the turbine faster. The vanes start to open at about 1500 rpm and contine to do so as the revs rise, not fully opening until max revs. There is no wastegate on a VNT turbine, the boost control is all provided by the vanes.

So the vanes are exercised by changes in revs. This can be done in a low gear, to avoid exceeding speed limits.

 

[Neo_VR]

Theres some good theory here

The problem ive got with mine is (especially in cold weather) before the engine is fully warm, the VNT blades are "lazy" means they sometimes stick in a position, so i dont get any boost until 2500 rpm, and if im cruising it drops into limp mode with charge pressure control: negative deviation code.

its always alright when its fully warm, but its a pain in the ass as i have to try to keep engine revs over 2500 when cold... which ovbiously isnt good for the engine.

 

[AndyC567]

The best thing you can do to reduce sooting-up of the vanes is to reduce the EGR activity, either by using VAG-Com to set the EGR to minimum or by blocking the EGR valve's activity (putting a blanking plate in the recirculation pipe, pulling off and sealing the vacuum line to the EGR valve or disconnecting the electrical connector to the N18 valve).

I agree entirely..

Easy to to with Vag-Com, takes about 2 minutes.

http://tdiclub.com/TDIFAQ/TDiFAQ-7.html#j

I have done this to my Toledo 1.9 TDI 110, and haven't noticed any difference in performance or MPG.
Sailed through the MOT test to !!

Nice to know my turbo isn't sooting up though.

 

[cheshire cat]

Theres some good theory here

The problem ive got with mine is (especially in cold weather) before the engine is fully warm, the VNT blades are "lazy" means they sometimes stick in a position, so i dont get any boost until 2500 rpm, and if im cruising it drops into limp mode with charge pressure control: negative deviation code.

its always alright when its fully warm, but its a pain in the ass as i have to try to keep engine revs over 2500 when cold... which ovbiously isnt good for the engine.

sounds like a strip and clean job