Hi

Octavia 02 reg - 1.9 TDI ALH engine.

I have sudden loss of power on hard aceleration when the car is loaded.

With the diagnostics on the Laptop I could see the manifold pressure drop but no errors are flagged.

Using Gendan Engine Check. No errors on a hand held code reader. Also used some other free ware and no codes.

So thinking that the car was loosing turbo boost I set up an elaborate test with Vacuum Guage on the turbo line, and oscilloscope on the Vac Valve ECU cable. and the diagnostics running.

youtu.be/mq8raUPwdV8

Finally - when the car is first used you can see the VVT turbo being controlled by the ECU with a square wave on the oscilloscope. When the engine looses power - no error is flagged but the ECU no longer sends a square wave to the turbo valve (just little spikes) - so the turbo is turned off by the ECU for sure.

So either the ECU has just turned off the turbo or it has completely dropped into "Get Home Mode" and did not flag any error when it did this?

On the good side - at least I know the ECU has turned off the turbo and that is why my engine has lost power. On the bad side WHY!!!! and what to do next?

Could a bad MAF or other sensor trigger this - noted on the forums that bad mafs do not trigger errors - Diagnostics is showing a good readout from the MAF - but the ECU in this case is dropping into safe mode?

Do you think another forum might have really tech'y people who gould help me delve a bit deeper?

I went to the local skoda dealer and started talking about the oscilloscope output and their faces glazed over.

The Car may be 02 reg but it has only done 60,000 miles. May years only managing 1000 miles with previous owner. Goes like a train when free of the fault.

Glad I am doing all these test I would probably be on my 5th visit to the garage with this obsure fault and £hundreds down.

Thanks Dave

Good old sticking turbo vanes by the sound of it.

Mr Muscle oven cleaner usually fix's the problem.

http://www.briskoda.net/forums/topic/279971-octavia-lk-110-tdi-estate-52-regintermittent-turbo-issue/

There's a discription of the mr muscle fix in there.

Wow gone to huge lengths to diagnose a common issue ;-)

Good to see mind don't see that much these days

Hi - thanks for the info - I will try cleaning the turbo with oven cleaner and will update the thread. Can't believe someone programmed the ECU to go into limp home and not put a code up to say the ECU did this and this is why. That is such bad programming and from VAG!

Tried the Mr Muscle treatment with only a minor improvement.  A good trick to get some major movement of the blades is to attach a pipe and suck on it to move the turbo with the MrMuscle foam in the turbo.  This is far more effective that wiggling the small lever. 

Mr Muscle did not cure the problem so it was a turbo off job.  It is tight behind that engine and a small 1/4 socket set made the job easier. I bought a second hand inlet maniforld on ebay £8 and burnt all the thick gungy carbon/oil out with white spirit, blow torch and compressed air. To clean it properly was a few hours job which saved time on the turbo off day.  Followed the guides.

 

 www.myturbodiesel.com/ 1000q/a4/VNT-turbo-removal-vanes.htm

 www.myturbodiesel.com/ 1000q/a4/turbo-removal-TDI-engine.htm

 

The problem was obvious when I took the turbo appart - fine rust build up from the casing obstructing the control ring.  Took the ring off and scraped the rust off with a craft knife. 

 

I was not sure of gaskets and was able to order a kit from the following company.

 www.darksidedevelopments.co.uk

They also do a flexible oil feed pipe which may make life easier if you need to cut the old one off.

 

I replaced those horrible clips on the air pipes around the actual turbo with jubilee clips.  The other clips I was able to get access to with a mole grip to get them back on again.

 

The only real problem I had was shearing the stud on the exhaust.  I got a replacement stud from the local garage.

 

As an amateur with not all the right tools it was about an 8 hour job.

 

Dave