v/w t5 v/v turbo overboost

hi
as anyone experianced engine goes into limp mode sometimes when accelarating ie to overtake on m/way or very steep incline? i am told this is a common problem with all v/w vans and cars, inc audi that only do low mileage, it is tempory fixed by simply by parking the vehicle switching the ignition of, then restart, and may be o/k for a short time or many weeks or months.
I am told by v/w the cause is the variable vanes in the turbo sticking caused by sooting up of the vanes and resulting in a overboost situation.v/w say that the only fix is a new turbo £1000 plus fitting.
any comments?

I have a 2001 Passat 2.0PDi 130 which I bought from a friend when he was experiencing this very problem. The garage told him that it needed a new variable vane turbo so he decided to part-ex it against a newer Jetta. I bought the Passat from him for what the garage offered him.

I bought a VAG-COM lead off eBay (about £10) and connected it to my laptop running VAG-COM/VCS Lite. This enables you to interrogate numerous 'controllers' throughout the vehicle. It was almost immediately apparent that inlet manifold pressure was permanently too low so I disconnected the inlet pressure sensor, then it went permanently high: problem located. I spent £40 at the local VW dealer on a new sensor and the car then ran perfectly and continues to do so.

Another component liable to failure is the so called N75 valve. This valve operates continuously to control the level of vacuum applied to the actuator which then operates the vanes of the turbo. On my Passat the bloke at the garage had substituted this to see if it would fix the problem and billed my friend, but it didn't.

The issue with the Garrett VNT turbos which is often mentioned is that the mechanism may jam with soot. This can be checked by disconnecting the vacuum actuator following which you can operate the vane mechanism manually. Mine was remarkably free when I checked it: so free that I thought nothing was happening. If you suspect sticking, watch the actuator mechanism whilst someone revs the engine and you might see some movement without removing the actuator. If you're adventurous the turbo can be dismatled to free the vane mechanism. But VAG-COM is a must. You can even record what's going on whilst you're driving then view traces of, say, demanded turbo pressure vs actual pressure which is great for understanding what's going on.

The moral of the story is don't listen to anyone advising you to replace the turbo without them having done a proper diagnostic test with VAG-COM or similar and understood the results.

If you want to know more about VW Diesels we are most fortunate in the existence of a superb website [You must be registered and logged in to see this link.] which covers the vast majority of VW Diesel problems with amazing clarity and detail better than your average Haynes manual.

Best of luck!


Bartfarst

PS my mate's 2007 Jetta subsequently suffered failure of the dual mass flywheel, exchange of which has induced clutch judder..and so on. A lifelong VW buyer is now ready to jump ship!

hi
many thanks for the info , i will try as you suggest,do we realy need v/v turbos, duel mass flywheels dsg gearboxes etc, etc we are only going camping.
thanks again
don

don battersby wrote:hi
many thanks for the info , i will try as you suggest,do we realy need v/v turbos, duel mass flywheels dsg gearboxes etc, etc we are only going camping. thanks again don

I agree Don. That said, if you have a turbo then you need either a variable nozzle technology turbo or a waste gate to dump excess pressure. But DMFs are a complete pain.

Bartfarst

don battersby wrote:hi, many thanks for the info, don

Don, did you make any progress with your limp mode issue?

Bartfarst