2.0 JTS inlet carbon - Alfa Romeo Forum
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(Post Link) post #1 of 6 Old 26-04-19 Thread Starter
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Warning 2.0 JTS inlet carbon

I think everyone knows about this by now. Direct injection = no fuel to wash clean the backs of the inlet valves. There are various theories about how this occurs but I think we can discount the oil misting from the crank breather straight away. Other ideas are catalytic action from inlet valve materials with the oil but I think my photos show that the most likely way is combustion gas backwash.

Anyway, this is my JTS before overhaul at 101k miles. At the time, performance was poor. Performance tailed off at 5000rpm and it really sounded like I was killing it if revved higher. There was also a nasty humming sound a bit like differential/gearbox bearings. A 1.8TS would easily be quicker.

Since rebuild, I try not to let the engine idle. At traffic lights I either switch off the engine or raise the idle to 1500rpm. I have used 10W/60 Shell Helix Ultra or Motul X-Power engine oil. Fuel used is Shell V-Power or BP Ultimate. about 2 months after overhaul, I measured the maximum MAF reading to be 460kg/hr. 30k on, I recently measured it at 459.4- which is a loss of 1kg/hr. My point is that I appear to not have significant carbon build-up on the engine and have shared my findings.

As far as oil use goes look at this thread for what is needed to solve;
https://www.alfaowner.com/Forum/engi...6-2-0-jts.html (Excessive Oil use - 156 2.0 JTS)

The inlet valves are certainly dirty but the engineer found about 5mm of carbon build up on the walls of the inlet valve throats. That is why a JTS does not breathe well at high engine speeds if carbon has been allowed to build up.
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(Post Link) post #2 of 6 Old 26-04-19 Thread Starter
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Cleaned JTS cylinder head

Obviously, I thoroughly cleaned the engine and had no carbon on it afterwards. The head was chemically cleaned/acid dipped but still needed a little bit of scrapping/rotary wire brush work. Unfortunately I did not take pictures of the inlet ports but the head looked better. The camshaft bearing caps were not given to the engineer. I cleaned them with Mr Muscle oven cleaner and a Scotchbrite pad.
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here's the photo I forgot to upload.
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(Post Link) post #4 of 6 Old 26-04-19 Thread Starter
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To spell things out, my MAF readings refute the oil mist/separate catch tank idea.

Not allowing the engine to idle (above 1500rpm the mixture becomes stoichiometric- stratified mixture can produce 10x the carbon deposits) produces less combustion gas backwash.

Decent fuel keeps the injectors clean and the link in the first post discusses why drillings in the piston oil ring valleys are necessary to reduce oil consumption.
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When the Alfa 2.0 JTS engine was changed from euro 3 to euro 4 specification one of the the camshafts (eper shows it as being camshaft A, not S but my italian is insufficient to know what this means) was changed (eper gives the replacement date as 16 Apr 2003); as I understand it this was to rectify the inlet carbon fouling problem.

The JTS engine relies on valve timing to re-circulate the exhaust gasses, there is no egr valve.
Quote from ItalianCar.net:
The use of stratified charge only at speeds around idle speed, however, allows the 2.0 JTS unit to use a conventional catalytic converter system. This result is also made possible by a more extensive use of exhaust gas recirculation, which reduces the production of nitrogen oxides (NOx). Because Alfa Romeo engines are fitted with variable valve timing, exhaust gas is recirculated to the intake on the 2.0 JTS directly between the intake and exhaust valves (internal EGR).

There were many other changes made at the same time, so possibly the valve timing was not the only problem. I can say however that my euro 4 2.0 JTS which has covered 127K plus miles, is very powerful indeed for a 2 litre non-turbo engine and far more powerful than my old 156 2.0 Twin Spark.
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(Post Link) post #6 of 6 Old 27-04-19 Thread Starter
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Thank you @sensingsys . Your comments are echoed here;
italiaspeed.com: Alfa Romeo 156: 2003 Restyling

What I will say is that my JTS was built 16.12.04 and registered 28.04.05 yet still had major carbon issues. VAG engines have carbon issues, even with turbo charging. It was Toyota who first completely solved the carbon issue with 4 direct injectors and 4 port injectors.

With all this information, it is clear that Alfa never completely solved the carbon issues, nor does use and good maintenance but we can at least significantly influence how much our engines carbon up.

My engine still produces a maximum MAF value of near 460km/hr and I'd be interested to know, @sensingsys , if your engine is near that value and if it was ever overhauled. Nonetheless, well done, as it seems good maintenance and use have kept your engine good.
I'd also invite others to post if their MAF value exceeds 460 kg/hr as now at least we have a yardstick to measure engine carbon.

It is the spectre of carbon which as prevents me from changing the camshafts for a performance set as the effects may be very short lived. This is a shame because the TS and JTS engines have larger valves than the Focus ST170 engine which is known to be able to produce 200BHP with only relatively minor modifications.
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