This perky brother to the 2.8 V6 first appears in the Audi S4, the Allroad and Audi A6 models early this century. The two smaller turbos spool up rapidly and give the engine an amazing power to mileage ratio. Like all turbo charged engines from this century, altitude is not an issue. Where normally aspirated engines drop almost 25% of their power by 6000 feet of altitude, the 2.7T Audi engine just spins the turbochargers faster. All it cares about it getting the proper pressure in the intake ducts. The 2.7T looses just a hint of power, and an alert driver may notice the increased turbo lag. The horsepower loss due to increased altitude has a lot of variables. There is a popular formula, but it ignores: Ambient air temperature, humidity, and barometric pressure, plus the engine’s intake and exhaust system flow, and cam characteristics.
Here is a qualified report of the quirks and failures, more or less in the order of the frequency of repair. Like other turbo motors, many of the repairs are heat related.
The plastic check valves in the engine Vee failed first, but all the plastic was doomed eventually. Hoses got heat rot, especially secondary air vacuum hoses. Some of the plastic valves and Tees are located under the intake manifold, and it must be removed to access them.
Oil leaks and more oil leaks are the hallmark of this engine. The 2.7T Audi motor had valve cover gasket and cam chain tensioner gasket leakage similar to the other v6 engines. But even the repairs did not last very long, especially if aftermarket gaskets were used. The turbo oil return pipe O rings at the oil pan were a common leakage point. That required dropping the subframe down to access the flange and O ring.
The 2.7T Audi engines all had an electric coolant pump to help cool off the engine and turbos after the motor was shut off. The pump was a common leaker, generally around 100,000 miles. That secondary coolant pump lived underneath the intake manifold, in the middle of the heat. The factory came out with a kit to relocate it down near the alternator. It was not worth trying, as the installation time added a few hours to the job, and it just would not fit on the Allroad and some A6 models. Better to just live with replacing the pump again if it went bad.
Oxygen sensors were a more frequent failure on turbo motors because of the extra exhaust heat. Many times the failure mode was because the O2 sensor’s heater circuit got hot and the resistance changed. In most models, when an oxygen sensor code shows up, it is correct, the sensor has an issue. Same here, but they just seemed to show up earlier in life.
Another common heat failure were the exhaust temperature sensors. Vehicles with a performance chip and a heavy right foot could sometime kill a sensor every year or two. This problem showed up more on the heavier Allroad model.
The diverter valves, also know as recirculation or dump valves, failed regularly, especially on the earlier cars. This could also cause the turbos to over speed if the valves failed open. Many of those valves got replaced with metal body custom valves. The rubber Y boot at the throttle body cracked and broke, causing intake leaks and boost loss.
The 2.7T Audi engines responded well to high performance chips power wise, but chip tuning did seem the accelerate all the other problems, as well as the demise of the turbos themselves. The chip technology varied wildly between manufacturers. Differences in boost pressure vs. ignition timing curves vs. injection volume could spell bone melting temperatures in the exhaust and intake of these engines in hot weather.
More than one 2.7T motor had a chunk of plastic suck down inside the motor when an old check valve failed. One would think that a tiny bit of plastic could do no harm, but sometimes it could go right through the engine and damage a turbocharger. The damaged turbo wheel would howl like the cops were after you. And often would do that forever without getting worse.
Secondary air injection pumps failed more in this 2.7T Audi turbo version than in the other V6 engines of Audi and VW. The pumps were redesigned and relocated where they were exposed to far more heat.
Coolant leaks became more common as the engines got older. Usually leaks came from the pipes that were on the back of the motor and in the valley between the two banks. Again the intake manifold had to come off for repairs.
On the odd side, we have seen one instance at Karmakanix where one head bolt hole stripped out during a head gasket job. The motor had been over heated, so block metal fatigue may have been the cause. A timesert with the top ground off so it could thread down into the recess in the block fixed the issue.