Why turbos need optimal conditions
Anyone who wants to give their peak performance needs the setting to be perfect. It’s no different for turbochargers! If there are disturbances in their environment, you will immediately notice problems in performance. We already reported elsewhere in our turbo series on the impact of a defective oil supply. Here you will find some more factors that can adversely affect turbos.
If the air has escaped: the damaged compressor
If the impeller is damaged, the air that has been drawn in cannot be sufficiently compressed and the necessary boost pressure is not achieved. The most common cause of this are foreign objects, which damage the delicate impeller blades.
Actions required: Always carefully examine the intake section and the compressor side of the turbocharger. Failure to remove all foreign objects following a repair can result in expensive consequential damage! When the compressor has been damaged by a foreign object, the charge air cooler must also be replaced, as splinters and fragments cannot be removed completely.
If you hear whistling, it’s a case of a leaky charge air path
If the charge air path is not leak tight, the built-up pressure escapes into the environment. You should therefore examine seals and charge air coolers very closely. Caution: old sealing rings in particular are prone to leakage when they are reinstalled!
A clogged air filter will also prevent a turbocharger from performing to its maximum potential: if the turbocharger cannot breathe freely, it cannot build up the full boost pressure!
Actions required: Always examine the charge air path meticulously. To do this, you should disconnect the hose system connecting the turbocharger to the engine using a special tool. And don’t forget to replace the air filter regularly—this will help you prevent expensive damage to the compressor due to foreign objects!
If it has stopped running: the damaged turbine
The turbine wheel is driven by the outgoing exhaust gases and transfers this energy to the impeller via a shaft. If a problem occurs here, the turbocharger no longer achieves the necessary speed and the boost pressure falls. The most common type of damage to the turbine wheel is caused by foreign objects. These are usually small parts that break off from welded manifolds, for example. However, tiny particles from the engine or charge air cooler can seriously damage the blades of the turbine wheel.
Actions required: Locate the damage on the old turbocharger, examine the manifold, and replace the charge air cooler.
If there’s a blockage: clogging on the exhaust side
The exhaust side can also cause performance problems: the exhaust gases need to pass through the turbocharger without significant back pressure. A blockage here may have a number of causes. In diesel engines, the source of the problem is most commonly a clogged diesel particulate filter (DPF).
Actions required: Check the pressure ratios downstream of the turbocharger and the loading status of the particulate filter. If it is clogged, you need to regenerate or replace it.
If the control system fails: defective controls
Boost pressure control is handled by several components. In particular, you should check electric valves, actuators, and vacuum hoses for damage and correct operation. If the wastegate and the variable turbine geometry (VTG) are no longer correctly controlled, this will be especially noticeable in the lower rpm range. Performance problems can also be caused by VTG guide vanes blocked by soot and deposits, or by jammed linkages. You will usually find such errors in the engine control unit’s fault memory!
Actions required: Check the fault memory and the measurement values under different load cases.
If the settings are wrong: modified calibration
Every turbocharger is calibrated when it is assembled in the factory. Alterations to the variable turbine geometry (VTG), for example, quickly lead to deviating boost pressures. If these values deviate from the target values, the engine control unit enters fail-safe mode in order to protect the components and dramatically limits engine output. The same applies to the wastegate: if the flap opens the bypass too early, power is reduced in the lower rpm range. If it opens too late, this can result in the turbocharger’s maximum rpm being exceeded.
Actions required: Do not modify the calibration under any circumstances!