Their is no way to make this long story short to explain 2.0T oil consumption. Bear with us. It used to be that intake carbon deposits were 90% caused by low quality fuel. In the case of the TFSI motors, the story is different. We poll our customers at Karmakanix to get to the bottom of every issue that we can. Every one of the carbon issue customers that we have had reports using high quality fuel from the filling stations that talk about the cleansers and have pictures of happy cars. No names, please. So a different explanation for high carbon issues is afoot. The diagnosis and cleaning procedures are on a separate webpage.
The majority of our 2.0T customers report high oil consumption when we query. The problem stems from the PCV (Positive Crankcase Ventilation) system, specifically from a pair of valves where the rubber is thinner than a bicycle inner tube. They seep. When the PCV valves leak full on, the engine idles poorly, the mixture readings in MVB’s are way off, a code is set, the check engine light is on, and the dealer will deal with that under extended warranty for most models of BPY. BPY only! If you have the next model identical to the BPY, no luck at the dealer. If you have the next series chain driven motor, also no luck. If you have 2.0T oil consumption issue, also no luck.
But PCV leakage is not the problem, PCV seepage is the problem with 2.0T oil consumption problem. The PCV system has two functions: Keep the crankcase from pressurizing under boost, and keep the intake system from sucking more than slightly on the crankcase. When one side PCV valve seeps the crankcase goes under vacuum at idle and the intake vacuum sucks the oil out of the motor. Proof of the problem is one cannot easily remove the oil cap while the motor is running. When the other side PCV valve seeps, the engine crankcase goes under pressure when the turbo goes into boost. That pushes oil around the rings, but the big effect is different. The turbo’s tiny crankcase drains into the engine’s crankcase. The turbo does not have positive oil seals, just some tiny devices akin to tiny piston rings, plus a splash plate like an old bug motor. Positive oil seals would never survive the 130,000 rpms of a wound up turbocharger. When the engine crankcase goes under pressure, so does the turbo, which then spits oil out into the intake and exhaust. Proof positive is to take off the intercooler hoses. If the intercooler has a lake of oil inside, the PCV seeps.
That cooked up oil gets into the intake manifold and onto the valves. Because the injectors shoot right into the cylinders, there is nothing to help wash the funky oil off the valves. It bakes into nasty gooey carbon. Once the valve pockets start looking like black teddy bears, the swirl of the intake air gets very disturbed. TFSI means Turbo Fuel Stratified Injection. Stratified means that that between the intake swirl and the direct injection into the cylinders, the mixture is only rich enough to go boom right at the spark plugs. Further down in the cylinder, the mixture is too lean to explode, but will burn along with the flame front. The building carbon progressively disturbs the swirl characteristics, and now the problem begins.
At first, a customer just notices that the cold idle is not quite right, and eventually a random misfire DTC shows up. Soon after, the stratified mixture starts to get wrong enough to produce misfires when warmed up. What follows is the nightmare. The spark plug fires, but the mixture does not explode, it just burns like a blow torch. The piston descends, with no real power, and continues back upward throwing flame out the exhaust port. The next cycle when the piston comes up on compression, the flame is still on and the injector fires into a flame thrower. The noise is tremendous as the piston gets thumped backwards in the bore. The sound is like the worst diesel nailing, way worse than any pinging or even detonation that you have ever heard. The chain driven motor (C***) is smart enough to sense the wild knock sensor voltages, and it shuts off the injection and ignition to the offending cylinder. The BPY (B**) just beats itself to death. The only way we can move one under power is to disconnect the coil for that cylinder. It runs much better as just a three cylinder, which is to say badly. A motor with that level of the carbon issue would break something within minutes if driven.
We cannot overstress the importance of 2.0T oil consumption in a TFSI motor? Even though the PCV was under warranty, the dealer would not help you. Unless there is a code for the PCV, which only happens when it leaks badly, the dealer will not get started. Most 2.0T oil consumption is because the PCV seeps. They will happily charge you to look at the problem. Oil consumption is not an issue for the factory unless you can prove that your engine uses over 1 quart per 1000 miles. They will help you ascertain the oil consumption with a visit every two weeks, The big problem happens long before that. Ask about their cost for decarbonization near the beginning of the conversation.
It needs to be mentioned that some of the later 2.0T engines driven by timing chains have a very rare problem with defective pistons. In those motors, the oil consumption issue seems to get worse in a short period of time. Generally the problem becomes noticeable between 50,00 and 80,000 miles, and within 10 to 20,000 miles becomes extreme. To date, Audi has warrantied a piston replacement job for many of these cars.
2.0T Carbon Cleaning and Diagnosis
After all just said, one might think that we should just go straight to cleaning out the carbon when one of these cars come in with a misfire. Actually, no. Diagnosis required. Most misfire problems end up being spark plugs or coils. A few have been damaged motors. The rest have been carbon.