Doctor Diesel

Does what it says on the tin

Dear Doc, as you have mentioned Wynnís products in your letter page, I would like to tell you of my experience with one of them. Some time ago, I realised that my car, a 2006 Vauxhall Astra 1.7 CDTi, had turbo overboost. The electronic light would appear and the car would assume low power mode. I knew it was overboost because I have a fault code reader which also has a live digital read-out. As it had only appeared briefly at about 3,000rpm, I decided to try Wynnís turbocharger cleaner. Well, it certainly did what it said on the tin. The overboost did not happen again, plus the engine seemed a lot more responsive. I had purchased the fault code reader as I was fed up paying £50 plus VAT to the garage men for the information. The reader has paid for itself already. Regards, 

Peter Duffy

Hello Peter. Very interesting, and good to hear from you. In spite of my age, I do recognise the names of frequent or memorable correspondents, like yourself! But this morning I had problems remembering the name of our new lady Prime Minister. I do wish I could forget the name of the new President-elect of the USA though! I almost mis-read your words initially. I tend to think of the word overboost in association with quite a few engines (Ford, Peugeot…) that employ what they also call overboost ñ a short term higher turbocharger boost intended perhaps to assist in overtaking, and other situations when you need as much power as is available. Manufacturers do not think this high power should be used continuously, and it is therefore time-limited ñ although as we know, many tuners will happily tweak your engine to that power level and beyond, with no limits on when and for how long, and with a clear conscience. Anyway, I have digressed, but intentionally and primarily for the benefit of readers. To clarify things, what you had was a situation where the boost pressure sensor was reporting to the ECU that the boost was too high for the defined engine conditions, and therefore it displayed the warning light, and dropped into “limp-home mode”. You don’t say how you got out of such situations and got your car home, before you found the cure, but I am guessing that after an ignition on/off sequence, the engine would restart, and then you would probably go a bit easy on the right pedal to prevent it happening again ñ or until the next time!

My diagnosis of this ñ and I think maybe a full diagnostic check would have indicated this ñ is that the variable geometry turbocharger blades were sticking, and not changing their angle, as intended, with varying engine conditions. That probably means that they were not feathering to reduce the boost when the engine speed and power output reached a certain predetermined value. As well as creating the overboost condition, there was most probably incorrect boost levels (generally always too high) in other engine conditions that created the lack of response and/or a flat spot. You’ve probably worked all this out anyway, but the Wynnís turbo cleaner obviously shifted the gunge that was preventing the turbo blades from swivelling properly, and it obviously worked very well. It’s a lot cheaper done that way than with a turbocharger strip-down, or even turbocharger replacement, that I’m sure some garages would suggest, and then happily charge you several hundred of pounds for. So well done Wynnís!

You are right, in that portable fault code readers are available at very reasonable prices, for example on Amazon. They are not always engine or manufacturer specific, so may not be able to offer as much detailed diagnostic information as a full in-garage manufacturer-specific diagnostic machine check, but they can be very useful for a bit of modest DIY ñ something otherwise difficult to indulge in on today’s complex engines.

Doc Diesel

To which Peter replied:

Thanks for your prompt reply. For the engine to return to normal, I only had to let the engine slow down and very soon the light went out and full power was resumed as before.

As I was monitoring the situation with my hand-held reader, I could see boost pressure rising to about 190 kiloPascals (100KPA=1 BAR) at about 3,000rpm. So I was reasonably certain it was then that the car entered limp home mode, and that overboost was the correct code that the reader showed. I do appreciate that there is a lot more to diagnostics than I will ever be capable of. 

Since the initial use of the Wynnís additive, where during its application black smoke billowed from the exhaust and there was a very alarming diesel knock from every squirt from the can, overboost has stopped. So, I have decided to use the turbo cleaner on a regular maintenance situation, say every 12 to 15 thousand miles. Subsequent use has not resulted in the smoke or knock. Even though I do not use supermarket fuel and I add Millers to the fuel at every fill-up, I feel that the gunge will gradually build up without using such a cleaning agent. 

I have had this car since 122,000 miles and have driven it for 36,000 miles. In September, I drove to Marbella and back with my wife for a wedding. The car went very well without any overboost, in spite of motorway speeds of 70 to 80mph for long periods. The trip did show up a design defect, though. The lock on the left-hand rear door failed due to a cable fault. To my annoyance there was no way of locking the door manually. The car had to be left like that outside various hotels until we reached Marbella and located the Opel agent. Is there any way to lock manually? There really should be! Regards, 


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