Doc, I got the van serviced by Scotts Garage last week. It has done about 2,500 miles since we last corresponded, and has gone into limp home mode three times since then. Twice when pulling a half tonne trailer on a long uphill gradient, and once when I provoked it, just to see if there was still a problem. I have been driving it very little myself, most of the driving having been done by a work colleague who has been under instruction to rev it enthusiastically now and again. It has had a full tank of double dose of Millers through it, and a couple of normal dose tanks. Jonny Scott is still of the opinion that it just needs more use of the turbo to stop it getting lazy.
Wiclif

Hmmm. That’s a little bit disappointing, although seemingly something of an improvement on the previous situation. Has anyone mentioned the possibility of the turbo vanes sticking? If they don’t “feather” when they should do when engine speed rises, to reduce the boost level, they will trigger an overboost fault, although I would have thought that would have given you an engine fault warning light display. Ask Jonny Scott about it, next time you’re passing. We did a test of a turbocharger cleaning product quite a few months back, which is supposed to clear sticking vanes – it’s called Revive, and you can find it on the web. But before you splurge out £45 to £50 on this, without any real faith that it will be the solution, Scotts should be able to check whether or not the VGT vanes are moving freely and being actuated properly, without much dismantling. There’s also a wastegate actuator valve named N75 that can malfunction, causing this sort of problem. Finally, covering all bases, you could try the MAF (mass airflow filter) cleaning trick, where on Bosch MAFs if you rev the engine above 3,000rpm just as you shut down, it creates a cleaning cycle where the MAF wire is heated to red/while hot, which burns off any oil residues. Worth a try anyway, a couple of times when you shut down, although I’m told you should not do it too often as it shortens MAF life – but then yours has had a good life already anyway, hasn’t it? Always good to hear from you Wiclif, but it would be nice to see an end to the saga, wouldn’t it. Best regards,
Doc D

Wiclif sent my reply to Jonny Scott, at Scotts Garage, who replied…

Hi Wiclif. My thoughts all along have been that the turbo vanes were sticking, hence my advice to make it work by allowing it to build full boost by allowing higher revs. I don’t see an issue with the N75 valve, nor do I see any issues with the vacuums or hoses; during the test drive I took with you and subsequent look I had during the service, I see nothing wrong with the data readings. If you remember, it didn’t fault the day I drove it with you, and unfortunately, with this problem being so sporadic, it’s going to be very difficult to pin it down exactly. From experience and based on the trouble codes retrieved and the live data I recorded, I’m going with sticking vanes in the turbo: occasionally, however, I’ve found no hard evidence to back things up, it’s merely that I’ve been here before and everything points the same way. How do we proceed forward from this point?
Jonny

Look forward to the next episode of this gripping saga! Doc