CT emissions, one for Dave21478

[Chancer]

My old banger has once again passed its CT, thats 10 years now on a 15 year old vehicle that was so cheap I only expected it to last a year, I just cannot kill it!

 

This time round it was borderline on the smoke test (diesel) and needed a little determination and tickling by the tester to get through, I had forgotten to thrash it to within an inch of its life before the test.

 

My question concerns the décrassage I see there were a few stages of this during the test and presumably had I given it a good ragging before the results would have been better but what exactly is being cleaned or blown out during the procedure, is it deposits in the combustion chamber? Combustible oïl/crud in the turbo or exhaust? The injectors? Or something else.

The vehicle is a VAG 1.9tdi mechanical injection pump, manual injectors, old school, no catalytic convertor it has zero oïl consumption (it wasnt fully run in until 250000 miles) and is smoke free apart from during the accélérations of the test regime.

As an aside, or maybe its relevant, the variable vanes on the turbo regularly stick during the warm up period at any time except summer, it causes an overboost and then runs on L.O.S. but only needs a flick of the ignition switch to come back to full power, it causes me little problem as I know how to prevent it or instantly reset it, I gave it a Mr Muscle enema followed by a good thrashing a couple of years back which definitely improved things, actually it was Lidl oven cleaner. The car is always driven very gently for maximum economy and still returns 60+mpg, I have changed from a hoonigan to an old fart!

[Harnser]

Not much else to do really except you could stick a bottle of decent injector cleaner in the 1/4 full fuel tank - something like Wynn's, and give it a good ragging just before the test.

This will possibly give the injector nozzles a bit of a clean and improve the spray pattern - finer spray - better combustion-less smoke- etc.

If you are driving it like miss daisy it's just not burning off the residues on a daily basis so it accumulates and causes the deposits in your turbocharger that causes the vanes to stick - which is cheaper? Fuel or a turbo stripdown?

Drive it like you stole it once every week!

[Chancer]

If I had done that with a car that had 200k miles on the clock when I bought it then it would only have lasted for the 12 months that I envisaged, when I was young I could kill a well maintained low mileage vehicle in a couple of weeks!

 

The turbos sticking is a very common problem no matter how they are driven, most people just trust the garages and get shafted for a new one at huge cost, my chauffeur pal who sold it to me replaced it with a Touran, new vehicle, loads of electronics when it happened no reboot possible, he paid out IIRC €4500 on 3 new turbos in the 3 years he had it, friends in France who drive like they stole it get shafted for €3K+ a pop, they usually trade it in and lose even more, my vehicle would have cost a French person conservatively €15k in new turbos in its 15 year life, it is still running fine albeit with an idiosyncracy on its original turbo.

 

As for what is cheaper, fuel or a turbo stripdown?  consider the above, I spent €2 on a can of décape four which will give my turbo and exhaust several more enemas if need be. Other owners will have spent 25% more on fuel than I plus all the repair bills.

[Chancer]

I will probably remove the injectors one day and solvent clean them, there is sometimes a puff of smoke on start-up indicating a dribbling one on shut down.

[dave21478]

The decrassage is to try to remove soot particles from the exhaust system. They collect in the silencers and the revving for the test can dislodge them and give false results.

There is very little that can stay in the actual engine or turbo that could affect emissions, the buildup is always further downstream.

Someone I know with a Megane Scenic (old style mechanical pump) has the driving habit of changing gears just as the turbo starts to spool up, so its permanantly labouring off boost. Every CT was an emissions hassle and the last failure resulted in me taking the exhaust off and power washing it out, which really killed off a patch of lawn!

Now when I take it down it gets a severe Italian tune-up on the way to the test centre and I try to time it so that its still spanking hot when tested rather than cooling down in the carpark first, although thats more to do with catalytic efficiency.

Worn injectors will give poorer combustion and more soot, but generally its beyond DIY to repair fully. I have used Diesel Bob in the Uk several times for injector and pump rebuilds at a tiny fraction of the costs of local places.

Also, modern diesel isnt great. All the soaps added mean lower lubrification of the components. 100ml of low ash mineral twostroke oil added to a full tank of fuel will help. I get noticeably smoother running after a couple of fillups, although if you have auxilliary heating like a webasto, they dont like that.

On LeBonCoin I see adverts popping up for "decaliminage" treatments offered by garages or mobile mechanics. Apparently this is the TerraClean system thats been in UK for a couple of years where they disconnect the fuel lines and run the engine on a "special" fuel delivered by their machine which .....does...something. People rave about it anecdotally but I suspect its the new snake oil, myself.

Hang onto that car as long as you can -modern diesels are a complete sh1t-show, to say nothing of the massively complex electronics stuffed into the rest of the car. Personally I will be sticking to petrol as much as possible for the future and either running older cars or keeping on buying moderns around the 500 quid or less mark so it can just be dumped at the first sign of imploding DMF/coded injector failure/FAP problems and all the other joys that will see cars scrapped earlier and earlier.

[Chancer]

Thanks, your first paragraph makes total sense and I get it!

No way am I going to pour some expensive snake oïl in my tank because a well meaning person on a forum or the CT tester says to do so without an explanation as to why.

 

Yes I have hung on to the vehicle all this time because I have seen just how unreliable and costly its replacements have been for my chauffeur friend, I could have had the top of the range high spec DSG gearbox Touran for £2K at 3 or maybe 4 years old but given what it had cost him in that time vs the Skoda costing me nothing I just did not need the grief just to be able to drive somethin newer which would only have created jealousy and bitterness where I live.

 

Also after 11 years of my neglect the vehicle is in superb shape, the steering wheel was shiny smooth but not even the drivers door has dropped, I replace parts like the springs and shockers etc with good cheap scrapyard replacements (off a cop car) but they were still functioning correctly.

 

The Tom-Tit shatnav and its auto turn on every 14 days saw off the first battery, I have replaced tailgate struts, one coolant sensor, one wheel bearing, a £20 scrapyard airbag module and just oïl, filters and brake pads in 11 years and 120k miles, nothing else, and that on a car that had already done 188K miles.

 

My neighbour has just bought a much newer one, its so familiar but every part has been slightly improved even down to the minor switchgear, not enough to warrant all the attendant deisel particulate filter problems etc.

 

What is DMF and FAP?