Polo TDI 2004 - intermittent power, smoke, turbo issue

Question

Car: Polo TDI 2004 1.4 with 190,000 km (118,060 miles) on the clock. While

Issue: driving it intermittently (distance/time are not factors it seems) it starts to spew black/dark grey smoke and all power is lost (feels like the turbo has turned off). If I turn the car off and immediately turn it on, it will not start - sounds very much like when it isn't turning over if the battery is dead. If I leave it for a few minutes I can start it without a problem and it drives fine.

Factors: Distance & time are not a factor, as I can sometimes get further and sometimes not before it starts happening. It seems more likely to happen in traffic situations, so stop/start driving. There are NO engine warning lights and the heat indicator is stable in the middle (so not over heating according to the indicator).

History: Turbo was replaced 40,000km (24,854 miles) ago and hasn't had an issue at all. Recently had some electrical issues with the fuses and cooling fan not working. Both of those are resolved, however before they did, the car did over heat twice and damaged a pipe leading to the turbo which caused the turbo to lose pressure. That pipe has also been fixed and a everything in the turbo is 100% when the pressure tests were done.

Any ideas what the cause can be?

Answer 1

A common fault on variable-vane turbos (which I'm not sure whether the 1.4 has) is hitting limp mode due to overboosting. This can happen if a turbo has had an easy life around town and is coked up, then you suddenly ask it for some performance down the motorway or similar. However, this doesn't normally come with any kind of smoke so I don't think this is your problem.

In your case, it sounds more like some kind of boost leak, a lot of VW platform cars suffer worn joints on various bits of intercooler pipework (the locking "knuckles" get worn down by natural vibration of the pipes and then when the turbo pressure builds up, it can pop one of these joins off). This wouldn't fix itself though, so again, I don't think this is your problem.

Only things I can think of are that either you have some kind of split hose which is opening up under a combination of heat and pressure (i.e. when the engine is warm) enough to cause a boost leak, or that something's going on with your EGR valve and it's not allowing enough airflow through (the black smoke is usually a sign that your engine is getting too much diesel and not enough air to mix it with, which is why it's a common symptom of boost leaks).

It would probably be worth you trying to find someone in your area with the VW diagnostics tool VAGCOM (or the newest version, VCDS). This will allow you to find out if the ECU has any fault codes stored which could take you straight to the problem, and will also allow the operator to perform various troubleshooting procedures (logging output of sensors etc) to find out what's happening. Check out any local VW/Audi/SEAT/Skoda forums (they're all the same cars underneath) and you'll often find someone willing to help out for the price of a couple of beers, much cheaper than taking it to your VW dealer.

Answer 2

I have a Polo classic 1.4 TDI Had the same problem of loosing power. The vacuum unit on the Turbo have a steel pipe, and a rubber vacuum pipe fit over it. The point of the rubber pipe get hot, or is hard on the tip, so I loos boost pressure. I cut a inch of it and replace it back with a proper clamp, and it look if the problem is something of the past.

Answer 3

It looks as if the unloading valve is staying open hence all the boost going to waste. The valve then intermittently closes to function normally and randomly stays open.