Exercising the Turbo "vanes"

[Neo_VR]

sounds like a strip and clean job

Sounds like a excuse for a hybrid you mean

 

[sssstew]

haha spot on Neo!

 

[cheshire cat]

Sounds like a excuse for a hybrid you mean

 

[jamesmckelvie]

sounds like putting your foot down under 2K in a high gear will reduce the life of the clutch.

 

[TornadoRed]

so what is the best way of getting the vanes to go through the maximum movement ?...ie get the "pitch" at its max ?

I think the way you drive isn't the real issue. The problem may be with the boost controller, referred to as the N75 valve in the VW TDIs.

If the VNT actuator itself is able to move freely, then presumably the vanes inside the turbo are also able to move. So you must find out if there's a vacuum leak in the N75 or one of the hoses connecting to it.

 

[asthpsw]

There is now vacuum leak. The problem is the vanes returning after full boost & as I understand it the return of the vanes is done by N75 valve having no vacuum or at least less vacuum than when under full boost. I understand that the vanes return under a spring load once the vacuum is released or lessened. It because the carboned up areas then offer resistance to the vanes returning to a lesser boost angle that I then get the overboost error when changing gear. The carbon builds up in an area in the turbo mechanism that isn't uded often enough by me.

 

[WhatTheHell...]

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.

Nicely explained mate, tdi at it's best boot it in 2nd 3rd 4th, too much in 1st will only trash ya gear box. where the tourque is. : )

 

[asthpsw]

If the engine has a DPF does this effect the amount of soot going through the EGR and blocking the inlet ?
With the development of the CR injection / ECU control is there less soot production to clog the Turbo Vanes?
Paul

 

[ckyliu]

Flooring a diesel engine at low revs in high gear is a great way ruin your DMF Probably less of a problem with the smoother CR engine but the torque spike generated in a PD will kill a DMF pretty quickly.

 

[Pimped up vario]

Nicely explained mate, tdi at it's best boot it in 2nd 3rd 4th, too much in 1st will only trash ya gear box. where the tourque is. : )

Mechanical advantage is better in a low gear meaning there is less resistance to the torque. I higher gear experiences more shear force as that gear is harder to turn and the teeth experience a greater force from the engine torque.

The vanes in my leon tdi got plenty of exercise. Quite a lot of right foot.