16v twinspark breather questions - Alfa Romeo Forum
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16v twinspark breather questions

Hi folks, need some help understanding the 16v twinspark PCV breather system. I have an early 147 with horrendous oil consumption and no sign of smoke so rather than broken rings or worn stem seals and other such things that cause visible smoke I am turning my attention to the breather system.

The car seems to use oil constantly especially at motorway cruising. I know the early cars have a thin eco oil control ring and I can accept that there is the usual oil usage. However the consumption is seriously high and I still can't believe there is no smoke and there is not a single oil leak on the engine.

The PCV velve is supposed to be closed at idle and closed at acceleration and high load such as motorway. It only opens between these areas such as light load slow driving and driving about town etc. The Alfa valve that goes into the plastic intake manifold (which I have done the spring repair already) does not seem to be the proper tapered needle valve design that limits the suction at high loads it seems more like a one way valve with nothing else.

I am wondering if we could get it to close properly at loaded conditions, then the oil vapour would not be pulled through so hard removing 'good' oil vapour as well as the blow by gases. There seems to be no separator like the V6 engines have returning condensed vapour back to the sump. It may be interesting to retrofit one and see how much oil is collected.

But The piping on the rubber elbow leading to the throttle body confuses me. There seems to be a second breather pipe that splits from the y pipe on the side of the head and goes in before the throttle body and it seems to have no valve at all. Obviously this is not on the high vacuum side however at high load all the intake tract is under vacuum to some extent making me think that the pre throttle breather pipe must pull a lot of gas through.

There also seems to be another pipe into the rubber elbow which I am guessing is the fuel tank canister vent?

So to condense all that rubbish into one question, what does the pre throttle breather pipe do and does it have a valve?

Should either or both breather pipe have a proper tapered PCV valve and would this help perhaps?

Cheers Guys and girls.

The best quote I ever saw after a review of the 164 QV, was "From now on I am only going to buy cars powered by Alfa V6's"

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The pre-throttle breather doesn't have a valve.
Only the post throttle breather has a valve.
That valve is to prevent there being an uncontrolled air path that would bypass the throttle-butterfly.
When that valve fails to close, you get a very high/uneven idle.

The biggest pull on the breather system will be during closed throttle coasting/deceleration.
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147ts plus bits

Alternatively, run both to a catch tank and block the intake holes.
Although saying that, mine seems to catch a grim smelling watery liquid quite quickly!
I have very little oil useage, but it was low beforehand.
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I've got an early 2 litre 147 TS and it has always used loads of oil with no smoke etc, I just top it up every other time I drive it and make sure I've got some with me on long journeys! 3 years and 22k miles later and it is still fine, just approaching 104k miles total.
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well, since you are talking about it, I'll share a thing I did to my 156.
I was having idle issues. to eliminate any problem with the valve, I fitted another O-ring (it has one on top) on the bottom of the spring to make it stronger and close better. not sure if it won't open when it is needed and what the consequences are...
your feedback appreciated!
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