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The Volvo Parts, Accessories &
Performance Specialists Since 1963

Diagnosing Turbo Problems

2021-04-01 - Paul Bertucci

Dealing with exhaust temperatures approaching 2000°F and spinning at hundreds of thousands of RPMs, a turbocharger is a delicate, high-performance piece of engineering...and yet, with modern high-temperature alloys and precision machining, a modern turbocharger can last the lifespan of the engine when cared for properly.

Bearings and seals

Symptoms of failing turbo seals include blue/white smoke from the tailpipe during acceleration, screeching sounds during acceleration, and reduced boost output.

Most Volvos have turbos that are both oil lubricated and water cooled, so they have coolant and oil feed and drain lines. If you have smoke coming from around the turbo near the exhaust manifold, the gaskets and banjo fittings for these lines are a common culprit for leaks, which become very visible very quickly when they drip on to the hot turbine housing or exhaust manifold.

Conversely, blue or white exhaust smoke in a turbo car is most likely worn seals inside the turbo that allow oil to escape from the center section into the intake or exhaust. Blue smoke indicates that the compressor seal is leaking as the oil ends up in the intake system and is burned. You'll see white or very light blue smoke when the turbine seal leaks and oil ends up vaporizing in the catalytic converter.

These internal seal failures indicate that the turbo center cartridge (CHRA) needs to be replaced, which we advise servicing sooner rather than later. If you start getting a "dentist drill" screeching noise, that's a sign of so much slop in the bearings that the compressor/turbine blades are starting to come in to contact with the turbo housing. At full boost and 180,000 RPMs, this is not good!

Intake supporting parts (the cold side)

Since the turbo is oil lubricated, it has both an oil feed line and an oil drain/return line. Turbo oil seals are really not designed to resist much internal oil pressure, so if there's a crimp or obstruction to the oil drain line, oil backing up inside the turbo will start making its way past the seals and in to the turbo, causing blue smoke galore.

Oil drain blockages can be exacerbated by "oil coking", or oil and sludge buildup due to extreme heat. Old school cars had optional "turbo timers" to keep the engine running for a minute or so after heavy running to allow things to cool down, but modern turbos that have water cooling onboard are pretty good at staying within safe operating temperatures. At most, all you should have to do is not shut the car off immediately after heavy running, and normal driving shouldn't necessitate any special care.

Not all turbo smoking problems are directly related to the turbo, but the extras plumbing involved in a turbo system can add some new wrinkles to tracking down smoke. Blue oil smoke under load may also be a plugged crankcase breather/PCV backing oil in to other parts of the air intake. Some oil leaking out of the turbo and in to the charge pipes is alright, but if your Volvo is smoking under load despite good cylinder compression/leakdown, you may have a severely clogged crankcase breather system pooling oil in the charge air pipes and sucking in the pooled oil under high boost.

A clogged air filter can also cause blue smoke. If the engine can't pull enough air through the filter, a vacuum will form on the compressor side and suck oil past the compressor seal into the intake tract. In turbo cars, that's another good reason to stay on top of annual (or more frequent, for cars in harsh conditions) air filter changes.

If your car continues to smoke after repairing these problems, be aware that the car may continue to smoke for 30 minutes to an hour after repairs as accumulated oil in the charge pipes is slowly carried in to the engine and burned off. You can speed the process up by draining oil from the lowest part of the charge air side (usually the intercooler).

Exhaust supporting parts (the hot side)

If excessive turbo oil consumption isn't resolved, you can cause problems downstream from the turbo: the extreme exhaust heat of turbocharged engines will turn oil in the exhaust in to carbon deposits in short order, ands you can clog your catalytic converter if this is left unchecked. The backpressure from a plugged cat will drag down engine power, fuel economy, and make it impossible to pass emissions tests.

The charge pipes

Between the compressor housing of the turbo and the throttle body lies the part of the air intake system we call the "charge pipes", as they're filled with "charge" (pressurized) air from the turbo. This includes the piping from the compressor to the intercooler, the intercooler itself, boost pressure and temperature sensors, and the piping from the intercooler to the throttle body.

Generally, when problems arise in this part of the system, it's in the form of a boost leak. A crack in the intercooler, a loose hose clamp, a tear in one of the rubber or silicone couplers between charge air pipes, all of these will result in air pressurized by the turbocharger leaking out in to atmosphere instead of making its way in to the engine and giving you more power.

In the event of a boost leak, the difference between 10 and 13 PSI may be hard for your butt dyno to detect, but on a modern high-pressure turbo car with boost pressure sensors it'll be more than enough to cause boost-below-target error codes, as well as system-too-rich codes: if the engine is expecting to burn at that careful stoichiometric balance of 14.7 parts air to 1 part fuel but you're losing some air before it gets into the engine, your oxygen sensors will detect the imbalance and you'll get error codes.

Given the pressure the charge pipes can be under and the flexible nature of some of the plumbing, boost leaks can sometimes only appear at high boost levels, making these problems frustrating to diagnose. Double- and triple-check those pipes and fittings!

Turbo control parts

In a turbocharger, two critical systems for controlling the turbo are:

  • The wastegate, which controls turbo boost by opening at the desired boost PSI and bypassing additional exhaust gases past the turbo
  • The diverter valve, which recirculates built-up boost back in to the intake when you lift off the gas pedal

Wastegate: the flapper valve

Volvo OE turbochargers are "internally wastegated," so when you hit your desired boost target, a valve cast directly in to the hot side of the turbo housing opens to stop further boost buildup. For example, a wastegate adjusted to 10psi will start to open this valve at 10psi of boost, which bypasses exhaust past the turbine and stops the turbo from spinning any faster.

This flapper valve is quite simple, hinging open and closed at the end of the wastegate actuator rod. Despite this simplicity, it can sometimes take damage because of the very high temperatures it's exposed to, either coming detatched from its arm or getting chipped or cracked from all those thermal cycles. Sometimes, cracks can also appear in the turbo housing itself, though these cracks usually have to go very deep for enough air to flow through them to meaningfully affect turbo performance.

Any of the problems described above, if serious enough, mean the flapper valve is effectively failing open: the turbo is always bypassing some or all exhaust, and therefore never builds full boost.

In some rare cases, the flapper valve can seize closed, which results in the turbo overboosting as it can no longer bypass exhaust around the turbine to slow itself down. This is a pretty unusual failure mode, and overboosting is more likely a failure in the wastegate actuator or turbo control valve.

The position of the wastegate valve on the hot side of the turbo means it's easy to inspect in most cars when the exhaust downpipe is disconnected. If you're ever upgrading your exhaust, that's an excellent time to inspect both the appearance and the actuation of the wastegate flapper. Move the wastegate actuator linkage near the flapper by hand, making sure you get good resistance from the wastegate spring, but also smooth movement (no binding, scraping, or catching) from the flapper and linkage.

Wastegate: the actuator

The wastegate valve is opened and closed by a spring-loaded actuator. A pressure line leading from the high pressure side of the turbo to the actuator is counterbalanced by the spring within the actuator; as turbo boost pressure increases, the pressure eventually overcomes the spring at the target boost level and starts moving the actuator linkage and opens the wastegate valve.

This carefully-coordinated dance of boost air pressure vs spring pressure can run in to problems if any part of the mechanical linkage between the two is in bad shape. If the linkage is seizing or binding, you'll see corresponding gaps in boost control, manifesting as bucking or surging.

In addition to corrosion and deposits, the linkage is also somewhat fragile: a lightweight linkage allows the wastegate assembly to move around quickly in response to boost changes, but also means the linkage is easier to bend or break by a careless hand doing repairs near the turbo.

Within the wastegate actuator itself, the spring can weaken over time, resulting in the wastegate opening sooner than normal and preventing full boost from being maintained. On OBDII cars, if commanded boost is more than about ± 1psi from boost pressure sensor readings, you'll start getting boost target error codes and the car may go in to limp-home mode.

Conversely, problems with too strong of a wastegate spring will have the wastegate valve not opening quickly enough, resulting in boost spikes as the turbo keeps building pressure before the wastegate can open in time to slow things down. This will also usually throw error codes, and is a pretty unsafe state to stay in: large or repeated boost spikes can destroy the turbo or engine if left unchecked, especially when other parts of the engine like the fuel system can't keep up with the extra boost.

A wastegate being adjusted too tight or a spring being too strong is unusual from the factory, but other linkage problems can manifest as any of the above, depending if the linkage is too loose or bent out of shape. A linkage with worn joints or nuts worked loose by vibration is common, so listen for a rattle from the back side of your engine, or reach back and see if you can wiggle the wastegate linkage yourself.

If the linkage is bent, then the wastegate will act as though it's adjusted too tight, causing the wastegate spring to open early and your turbo to not hit target boost. Some wastegate linkages have bends in them from the factory to clear other turbo components, so if you suspect your linkage is bent, compare it with photos of your particular car's turbo online to make sure you have nothing out of place.

Wastegate: the TCV

In modern turbo cars, boost pressure isn't exclusively controlled by the wastegate-spring-to-boost ratio: the Turbo Control Valve (also sometimes called the Boost Pressure Solenoid) sits inline between the wastegate, inlet pipe (low pressure) and charge pipe (high pressure) parts of the system. The wastegate still controls turbo boost, but the TCV controls the wastegate.

By varying the ratio of flow between the low and high pressure lines on the way to the wastegate, the wastegate spring operates against TCV-deflected pressure, rather than just at the raw spring pressure = boost pressure in a wastegate-only system. In this way, our one little valve gives us computer control over boost pressure, allowing the car's ECU to pull boost in dangerous situations or in limp mode, to level off boost when the target engine torque is reachedto increase boost in overboost or sport modes, or to increase relative boost at elevation.

TCVs do fail from time to time, with underhood heat and oil mist in the lines doing their part to gum up the works and overload the solenoid. IPD offers our HD TCV with a sturdier solenoid and heavy duty internal seals to address this problem on P80, P2, and P1/P3 cars.

The flexible rubber (or silicone) lines between the TCV, turbo housing, and wastegate are also worth checking, particularly if they're OEM lines made of the sort of rubber that tends to become cracked and brittle around the 10-year mark. Replace these first if you have symptoms of a failing TCV, such as boost-below-target errors, errors specific to the TCV itself, or a lack of top-end power in high boost situations; because the TCV can keep the wastegate closed past normal spring pressure, a bad TCV results in the turbo falling back to wastegate spring pressure and thus not hitting the car's target maximum boost.

Diverter valve: the diaphragm

Air, especially compressed air, has mass and velocity. This means that it takes a little bit of time to make its way through pipes, and the mass of that boost air has kinetic energy when it hits an obstruction.

When you lift off the gas pedal and the throttle snaps shut, there's still some residual boost moving through the charge pipes, and it begins to pile up behind the now-closed throttle and back up in the pipes until it starts pushing back on the still-spinning turbo. This "compressor stall" or "compressor surge" of air pushing back against the blades slows the whole turbo down, causing turbo lag when you get back on the gas because the turbo has to work itself back up to speed. Over time, compressor stall can even damage the blades and bearings of the turbo.

This is where the Diverter Valve, also sometimes called the Compressor Bypass Valve or Compressor Recirculation Valve, comes in to play. When you lift off the gas and the throttle closes, you're increasing pressure before the throttle body, but you're also increasing vacuum after the throttle body as the still-turning engine is trying to suck in air that can't get past the closed throttle. The DV is pulled open by that closed-throttle intake manifold vacuum, allowing that excess pressure to vent from the charge air pipes to the turbo inlet and therefore preventing charge pipe pressure build-up to the point of compressor stall.

In later Red Block and all White Block engines, the inside of the DV uses a spring and a rubber diaphragm, with the spring serving to keep the DV closed until there's post-throttle vacuum or boost beyond a certain PSI. Over time, we've seen these springs weaken and the rubber diaphragm tear, resulting in a constant, minor boost leak from the failed-open DV. This can cause boost-below-target errors and "transient boost" problems, or slow boost buildup when getting rapidly on and off of the gas pedal (like when upshifting in a manual car).

To remedy this, we offer an an HD CBV diaphragm and spring kit for P80 and P2 cars, our "BoostAbility" CBV relocation/replacement kit for P2 cars (including the S60R and V70R), and performance piston-style diverter valve replacements made by Turbosmart for P1/P3 T5 and T6 cars.

Diverter valve: the vacuum line

In P3 T6 cars, the DV/CBV is called an Electronic Compressor Recirculation Valve, so named because it uses a solenoid to move a piston open and closed based on the throttle position sensor and boost pressure sensor, instead of using post-throttle vacuum to pull open a rubber diaphragm. Volvo likely went with this later system to address problems with CBV reliability, as we've found eCRV failures to be less common.

The vacuum-and-diaphragm system of P80s, P1s, and P3s is technically simpler, but the rubber in the system simply does not last forever. When chasing down CBV problems, also make sure to check the rubber vacuum line that runs from the CBV to the intake manifold.

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