Turbo/sensor issue

[admac21]

I've been having an issue with the turbo cutting out on my 1.9 TDi 110 Leon. It's an intermittent issue and it will always cut out around 55mph. I live on the edge of a city and don't often have the car above 40mph, but when I do, the turbo will sometimes just die right around 55mph! Pulling over and turning the engine off/on will usually resolve the issue allowing me go above 55mph without the turbo cutting out, but it has on occasion done it twice in a row (never had to turn engine off/on more than twice though to fix issue) So that's leading me to believe it may be a sensor issue rather than the turbo itself. I also have my One S hooked up to car with Torque and I got the following fault code: 'P0234 - Powertrain, Turbo/Super Charger overboost Condition'. Google didn't prove too helpful with this code. I was just wondering if any of you fine chaps had an idea of what might be going on?

TL:DR

Turbo sometimes cuts out around 55mph
Turning engine off/on will usually fix issue
Error code 'P0234 - Powertrain' from Torque Android App
Need help =[

Thanks!

 

[Allan_84]

you have overboost and the ecu puts the engine into limp mode = low boost.
when you engine off/on will take the ecu out off limp mode.
maybe your VNT part of the turbo is stuck

 

[admac21]

Alright, that seems to make sense from what is happening. Is the VNT easy to remove on a 1.9 110 tdi?

Thank you for your help so far!

 

[Allan_84]

VNT is part of the turbo

 

[Muttley]

Your usage - mainly low speed/city traffic and the code point strongly to the well-known "sticky turbo vanes" problem.

The VNT turbo on the TDI 110 (and most of the other TDI engines) uses vanes in the impeller section of the turbo (the exhaust side, the side that drives the turbo) to vary the size of the gas passage into the impeller itself, closing to speed up gas flow at low revs (=low gas volumes) and opening as the revs and gas volume rise.

Soot can build up in the vane section, making them stick under load. They stick at a part-closed setting (usually the revs that the engine sits at most often - so low to mid range if you commute/run in traffic a lot) and when you demand more revs, the higher gas volume results in turbine overspeed, thus overboost, and this triggers limp mode.

There are various cures. One is to get the turbine hot and keep it hot for a few minutes to burn off the soot. Uphill at 70mph in third for a few minutes is a good way to do it. This is often called the "Italian tune-up", from the practice employed many years ago of Ferrari techs when presented with a car that wasn't behaving (because it had only been driven slowly in town and/or to show it off). They would take the car for a drive over the test track and give it some stick, which was all that was needed.

There are also liquid compounds (much like oven cleaners, but safe to pour into your exhaust system) that can be poured into the turbo to dissolve the soot.

Finally, the mechanics option is to remove the turbo, open it up and clean the exhaust turbine. Not the easiest option - access is limited, and the nuts and bolts will be corroded and stuck after years of heat cycling.

 

[admac21]

Thanks very much for the reply guys! And thanks for being so detailed Muttley! I'll give the "Italian tune-up" a go and report back with the results, failing that I'll have a look into getting that cleaning compound for the turbo, where exactly would the cleaning compound be poured into?