In this video, Andrew Markel discusses what can cause a turbocharger to lose the ability to generate pressure. The main causes of turbocharger underperformance can be damage to the blades of the turbine and shaft damage that controls the turbine’s relationship to the housing. This video covers the external conditions that can cause this type of damage. Sponsored by TrakMotive.
Today’s 4-cylinder engines can generate more torque and horsepower than yesterday’s V-6 engines and turbochargers have made a comeback. Their location under the hood will determine lifespan and efficiency. Doug Kaufman explains why the placement of the turbocharger is so important. Sponsored by MAHLE.
Video courtesy Underhood Service.
You are probably seeing more turbocharged four-cylinder engines at your shop. Domestic manufacturers like GM and Ford have powered a wide variety of cars and SUVs with small displacement turbo engines. Also, import manufacturers like BMW, Nissan and VW use turbos on base engines and high-performance engines. Turbos are not a new trend; many applications have been on the roads for more than a decade.
The three things all of these engines have in common are intercoolers, plumbing to connect the turbo to the engine, and valves to control boost and turbine speed.
The signs of a leaking turbocharger system start with a lack of power or random misfires. In some cases, the escaping boost pressure can be heard. But, if the wastegate or bypass valves are leaking, you might not hear any noise. If you get a vehicle in that is not generating enough boost, don’t automatically assume it is the turbocharger. Modern turbochargers rarely fail due to problems with the internal clearance problems with the turbines and shafts.
Most systems use multiple sensors to monitor turbocharger performance. The boost pressure sensors, MAP sensors and throttle position work together to make sure the desired pressure matches actual pressures.
If the ECM sees a large enough variance in the boost requested and the boost measured, a code will be set. The code could have the wastegate, diverter valve or sensor listed in the description. In most cases, the part contained in the code is never the one that has failed. The source of the over or under boost condition must be addressed first.
On most engines, the intercooler is in front of the condenser and radiator. The location leaves the intercooler vulnerable to damage. But, one of the most susceptible areas for leaks are the mounting tabs that connect the intercooler to the vehicle. Vibration can weaken the tabs on the side tanks and cause a leak. This is why in most cases, when an intercooler is replaced, it needs to replaced with new hardware and isolators.
Condensation can also build up in the intercooler when the vehicle operates in high humidity conditions. The condensation can cause misfires under high boost and load conditions. Also, the water in the intercooler can freeze under certain circumstances and create a restriction until the engine or radiator can melt the ice. Some intercoolers have tiny holes at the lowest point to drain water and even oil.
All turbocharged engines need a way to control the pressure in the intake manifold. The pressure can be managed on the exhaust side with a wastegate, or on the compressor side using a diverter valve.
One of the most leak-prone components is the boost diverter/bypass control valve on the compressor turbine. When the valve ages, the spring gets weak, and the seal can leak under higher pressures. The actuation can be done with pressure/vacuum or an electric motor.
Wastegate valves on the exhaust side are pressure pots with a diaphragm where pressure works against spring. Old-school systems opened when the pressure reached a level where it could overcome the force of spring and open the wastegate. Modern systems manage the pressure with a solenoid so the actuation of the wastegate is more controlled. Some turbochargers now have an electronic wastegate that uses a motor to actuate the wastegate.
Wastegate leaks are typically caused by poor actuation of the wastegate caused by a weak spring or the line feeding pressure to the actuator. But, it is possible the valve and arm can be damaged.
A leaking wastegate will prevent the turbocharger from spooling up and the compressor from building boost. This will result in a loss of power.
Diagnosing an under-boost condition on a modern engine requires a scan tool that can graph multiple data PIDs from the data stream. The two most important parameters to look at are the desired boost pressure and the actual boost pressure during a test drive.
The first thing to see is if the boost reaches the desired level. If the boost is low, it is a sign there might be a leak in the system. If the boost is slow to build, it could be a sign there might be an issue with the wastegate or bypass leaking.
The next parameter is to look at the position or duty cycle of the bypass or wastegate valve compared to the boost pressure. Look for a change in position and a change in boost pressure.
Another essential piece of equipment is a smoke or leak detection machine. Your regular smoke machine used to diagnosis EVAP problems might not work because boost levels are, in some cases, five times higher than EVAP testing requires. But, there are high-pressure smoke machines that can detect leaks in turbocharger systems.
Article courtesy Underhood Service.
With more and more vehicles employing a turbocharger to achieve power and fuel efficiency from a downsized engine, the importance of maintenance is more critical than ever. Up to 50% of turbocharger failures are due to oiling problems, which can result from the lack of lubrication or not cooling down enough after the engine is shut down.
Today’s turbo systems are designed to reach maximum boost pressure with minimal lag time. Some OEMs are using smaller turbos that spool up quicker and reduce lag time, but they also run hotter the more RPM they turn. Most modern turbochargers use a “plain” bearing system to control the main bearing shaft’s movement.
There is a thin film of high-pressure oil supporting the shaft so that it floats while it rotates. Despite the film of oil that creates an oil wedge for the bearing to ride on, modern turbos can rotate at more than 240,000 RPM, or 4,000 rotations per second, and build up heat quickly to move the air.
Turbos need proper lubrication and cooling to handle the stresses of high RPM and everyday driving, which is why many manufacturers recommend synthetic oil because it can better handle higher operating temperatures without breaking down. If your customers are not doing regular oil and filter changes, it can lead to varnish deposits, sludge and, ultimately, bearing shaft failure.
Of course, some turbo failures are not because of lack of maintenance. Some failures are due to faulty manufacturing (although very few). Nissan, for example, issued a recall for certain 2011 Jukes due to a defective weld on the boost sensor bracket. Nissan says the weld may break and separate the air inlet and cause the vehicle to stall. One Juke owner had to replace the engine and the turbo because the turbo blew shards of metal into the oil line and subsequently destroyed the engine in the aftermath.
A rebuilt turbo may be an option on some vehicles, but many will need to be replaced with an OE unit, which is a lot more expensive. Either way, it’s a good idea to tear apart the turbo to get to the bottom of a problem and keep it from happening to the new one. The shaft bearings are usually the first thing to check if a failure is suspected. If the shaft was out of balance or oil starved, it may have telltale signs of damage like grooving, pitting or caked-on oil. It may not spin freely due to bearing damage or a broken compressor wheel.
Turbos that are water-cooled feed coolant through the center housing around the bearing shaft. The bearings also rely on the supply of oil for lubrication so they don’t get too hot and cause oil coking at normal operating temperatures.
In water-cooled turbos, coking is less of a problem, providing the oil is changed regularly and quality engine oils are used, such as a synthetic or one for high temps.
If the oil supply to the turbo is restricted during high-speed operation, even for a second, the buildup of heat can cause contact between the shaft and bearing surface. This can eventually lead to shaft seizure, and a death sentence for the turbocharger.
When the engine is shut off, the turbo still needs to cool down. If not, it can heat-soak the housing and oxidize the oil, forming coke deposits that act like as an abrasive to wear the bearings. Most late-model turbocharger-equipped vehicles use a pump or accumulator that runs after the engine has been turned off and the keys are removed from the ignition. These pumps can run for a few minutes to 20 minutes after shutdown. The health of the battery is critical with these systems. Many of them have smart battery monitors that will reduce the pump run-time so the car will be able to start. Also, these pumps can be used to pre-lubricate the turbo during startup.
If oil starvation is suspected, check for a low oil level, oil leaks or a restriction between the turbo and engine, or low oil pressure. Idling the engine for a few minutes to allow the turbo to cool down can prevent oil starvation. An aftermarket oil accumulator can also be used to keep the oil pressure up for a minute after the engine is turned off. These systems are also useful for preventing dry starts and serve as additional insurance against turbo failures.
1. Check the oil supply line for mesh filters in the supply line for debris. This is a common problem on Subaru models. Subaru recommends that the screen should be removed if the turbocharger is replaced.
2. The copper washers on the banjo fitting of the supply line are one-time-use items. If the line is removed from the housing, these need to be replaced because the copper and O-rings are formed during the initial tightening.
3. Make sure the ECM is running the latest calibration. The latest calibration can make a difference in the life of the turbocharger by lowering exhaust temperatures and increasing key-off cooling times.
4. Make sure the filter is positioned correctly in the housing. With the blades of the turbocharger spinning at over 100,000 RPM, even the smallest piece of debris in the air can damage the blades. Also, if an air filter becomes obstructed, it can cause a pressure differential that can damage the filter and allow unfiltered air to enter the engine.
5. High crankcase pressure is bad for the oil return line of the turbocharger. If the pressure is too high due to a blocked PCV valve, the return line on some engines will not drain when the engine is idling.
6. Some 2011-‘12 Ford F-150 models equipped with a 3.5L EcoBoost V6 engine may exhibit an intermittent stumble and/or misfire on hard acceleration after an extended drive at highway speeds during high-humidity conditions. The cause of the problem was due to condensation trapped in the intercooler. Ford’s solution was to remove the air deflector from the top of the Intercooler and install it on the bottom to help vaporize the condensation trapped at the bottom of the intercooler. The other fix was to make a tiny hole at the bottom of the intercooler that allows the water to drain. The full details can be found in TSB 13-8-1.
Article courtesy Underhood Service.
The basic concept of any forced induction system is to put more oxygen into the combustion chamber. More air in the engine means more power at the crankshaft. But, pressurizing the intake manifold means vacuum is replaced by pressure. This creates problems for managing vapors and pressure in the crankcase.
Natural Crankcase Pressure
On a naturally aspirated engine, the pressure in the crankcase increases and decreases with changes in engine load and speed. Gases from the combustion chamber can leak past the piston rings as the cylinder goes up during the compression and exhaust cycles.
As the piston travels down during the intake cycle, gases, oil and vapors in the crankcase can be sucked past the piston rings and into the combustion chamber.
Crankcase vapors are routed through the positive crankcase valve (PCV). The PCV valve is a simple spring-loaded valve with a sliding pintle inside. The system allows the vapors to be siphoned into the engine using engine vacuum.
Boosted Crankcase Pressure
When an engine is turbocharged, the intake manifold is under pressure during most running conditions. The gas and oil bypassing the rings are still present. And, the pressure generated by the turbocharger can increase crankcase pressures. That’s when a more advanced PCV system is required.
Vacuum is present before the turbocharger. On some engines, the vacuum is greater than the vacuum generated by the pistons moving downward, but not all the time. Vacuum is generated only when the turbo is spinning. The area before the turbocharger is typically where the vapors from the crankcase are fed into the engine. Some turbocharged engines will feed crankcase vapors to the intake manifold with a bypass valve when the turbo is not creating enough vacuum.
Turbochargers do not like ingesting the oil that can be found in crankcase vapors. The oil can form carbon deposits on the vanes and housing and cause a loss of boost.
Modern turbocharged engines have large oil separators typically incorporated into the valve cover or on the side of the engine block. The crankcase pressure is not managed by a simple check valve. Pressures are monitored electronically or mechanically at both the crankcase and intake. The system directs the vapors to either before the turbo or intake manifold when the time is right.
These next-generation PCV systems can fail because they are exposed to high temperatures and combustion gases that can damage plastic, flexible diaphragms, and seals.
If the system starts to leak, it can allow unmetered air to enter the intake. This can cause misfires and lean codes. In some cases, the pressure generated from the turbocharger can find its way into the crankcase if the system has failed. This extra pressure can cause oil leaks. If the pressure is great enough, it can even restrict flow coming from the turbocharger oil return line, thereby shortening the life of the bearings.
Article courtesy Underhood Service.