1.4 Tdi FAILSAFE Mode

[45bvtc]

An amazing tool this 90BHP 1.4 Tdi Audi A2 and I/we're still HAPPY! Love it's go-kart manners, subepr braking, around town 1st and 2nd gear acceleration; handling, and parkability.


Only issue so far is turbo overboost that results in the car going into 'limp mode'


Reason for this is that the variable vanes in the turbocharger housing are a tad coked and/or rusty and don't move as freely as they should on light throttle and so with no waste gate the system goes into fail safe.


Resolution 1) is to stop the car, turn everything off, and re-start - problem solved


Resolution 2) is to use a heavy right-foot as the issue occurs on light throttle only


Resolution 3) is to strip the turbocharger and clean the rust and carbon from the vanes.


I'm currently employing resolution 2 (and its still running @ 48mpg), and when necessary a switch off and on again as described in resolution 1.


I do find that when employing resolution 1 on the M6 at 70mph say that when relighting the motor that while the turbocharger is readily reactivated the power steering goes to sleep; but that ain't a problem for me on the M6


Best resolution is 1, stop the car, turn everything off, and re-start and then...


Hope this helps...

 

[desertstorm]

If you need some help with option 3 here are the removal instructions from Elsa Win, Unfortunately no where near as easy as a lot of cars.
It's possible the solenoid valve block is at fault but as you say more likely coked vanes.

Karl

 

[45bvtc]

As always Karl, thank you

 

[45bvtc]

Into 'limp-mode' TWICE on the M6 yesterday and both times on a light pedal and low load - and that's typical and characteristic of variable-vane turbocharger installations as these do not have a wastegate/dump-valve so the ECU goes into limp-mode.

So now going for option/resolution 3) and will be stripping the turbocharger and clean the rust and carbon from the vanes.

Note: this A2 though relatively low 82K mileage had been used primarily on short, local, town journeys, and had been using the cheapest supermarket diesel available: when I first drove the car the amount of 'crap' that came from the exhaust obliterated anything and everything at the rear; but I guess the damage was already done.

Since purchase in February the car runs only Shell diesel with an additional cleaning additive and general performance is amazingly good and the low speed torque incredible.

Note: this is a typical issue with variable-vane turbochargers so any of you guys using similar on more modern VW/Audi diesels make sure you use the best low-deposit fuels available.

 

[desertstorm]

It's the way to go, removing the turbo and cleaning it, rather than trying to use some chemical cleaner.
The VNT relies on heat to keep the carbon build up at bay. A good Italian tune up every now and then will keep them clean, Unfortunately once coked up that isn't usually possible.
I know when it's sorted it will be getting a regular Italian tune up won't it John .

 

[45bvtc]

Turbo de-coke underway Karl; I'll let you know when done and we can arrange a look-see...

Otherwise, this A2 is MEGA: so much fun, love it lots...

Better with a DSG for me mind, I keep forgetting to CLUTCH!

 

[45bvtc]

VVT decoke: every picture tells a story, and Suzy is oh so much better now...

Before:

And after:

ALL VVT (Variable Vane Turbochargers) NEED the occasional decoke...

 

[desertstorm]

Looks like a new one, looks like a lot of loose rust and scale in the mechanism, hopefully it will be better now.

Karl.