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A defective turbocharger: Why a DPF could be the cause

Replacing defective turbochargers is part of everyday working life in car and commercial vehicle workshops. One cause of the damage may be a clogged diesel particulate filter.

There can be many reasons for a defective turbocharger. Often the turbocharger itself is not the actual problem, but rather the problem is caused by malfunctions or defects in the peripherals. The service life of a turbo is also not necessarily determined by its age and mileage. We will give you an interesting example.

The damage pattern: From damaged to defective turbocharger

Turbine shaft — Due to the axial displacement of the rotor shaft, the compressor wheel was pushed into the housing and brushed against it around the entire circumference. Photo: BE TURBO

Every mechatronics technician knows that turbocharger damage can be a secondary fault. Simply replacing the defective turbocharger does not bring the problem to a close, as workshop customers will be confronted with the same problem again a few weeks later. Wolfram Kotte, technical trainer and key account manager at BE TURBO, reports on a Hyundai H1 with a 2.5-litre CRDi engine. After just 5,000 km, the new turbocharger was defective again. The damage presented with a deformed compressor wheel, causing an abraded housing and a worn thrust washer. Kotte notes that a broken turbine shaft is also not uncommon with this type of damage.

The cause: Clogged diesel particulate filters

"In the case in question, the damage was caused by axial displacement of the rotor shaft due to excessive exhaust back pressure. The excess pressure was caused by a clogged DPF", reports Kotte. Many people are unaware that a back pressure of 0.3 bar may be enough to shift the turbocharger's rotor shaft. This overloads and wears the axial bearing's thrust washer, and the gap between the compressor housing and compressor wheel is reduced until the wheel touches the housing. The abrupt braking effect can even cause the turbine shaft to break. Therefore, if the exhaust back pressure increases, the DPF must be cleaned or replaced. Simply replacing the turbo does not solve the problem.

Error detection

Pressure ring — The wedge surface (support) of the thrust ring is worn all the way round, meaning that the turbine shaft was pressed axially into the compressor housing. The oil supply can be seen on the right. As a result of the heat, the bore became carbonised and the oil supply was interrupted, which greatly accelerated the wear. Photo: BE TURBO

According to Kotte, the engine of the Hyundai H1 (year of construction 2008) was not yet fully monitored by sensors. For this reason, some actual values on the H1 and similar models cannot be queried via OBD, including the exhaust back pressure. This can only be determined manually using a manometer. "The hole in the lambda sensor is suitable for mounting the measuring device on this vehicle. The probe is removed and an adapter for the hose is inserted. Alternatively, you can drill a measuring hole and then insert the adapter for the manometer there", explains Kotte. On vehicles with an SCR catalytic converter, the manometer can also be adapted to the differential pressure sensor; the Hyundai in question still has an oxidation catalytic converter. According to Kotte, the measured values must always be below 0.3 bar during a test drive.

Extensive background knowledge

In fact, it is important to bear in mind that a defective turbocharger can be caused by numerous things. For example, the damage may be caused by problems with the engine ventilation, the sensor system or the control lines. Engine oil that is contaminated or too cold is also a potential cause. "Turbochargers are integrated into the periphery, into the intake and exhaust system, and numerous factors influence the component. You therefore need the appropriate background knowledge to track down the cause of the damage", says Kotte.

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