VNT turbos

Since the late 1990s many diesel cars have been fitted with a Variable Geometry Turbocharger or Variable Nozzle Turbocharger. These turbochargers are very effective in minimising the effects of turbo lag, resulting in a more responsive throttle especially at low engine speed. These systems work by changing the speed and direction of the exhaust gases onto the turbine wheel. The most common of these systems is Garrett’s VNT ® mechanism which incorporates a ring of small movable vanes around the turbine wheel. Variable-vane turbo cutawayThese vanes are often referred to as the speed control mechanism. At slow engine speeds, the vanes are in the “closed” position narrowing the gap between them which effectively accelerates the exhaust gas onto the turbine wheel. At high engine speed the vanes open up slowing the exhaust gases, which stops the turbocharger from over-boosting. In most cases this level of control negates the need for a conventional wastegate. Despite these benefits, such turbochargers can be prone to problems. The speed control mechanism is easily affected by carbon build-up, which, if it becomes excessive, can cause the mechanism to jam. This can occur quite quickly if the vehicle is used for lots of short journeys where the engine is not allowed to get up to full operating temperature. It could also be indicative of a fuelling problem.The mechanism normally jams in either the fully open or fully closed position resulting in no boost or too much boost from the turbo. If the turbo over-boosts there is a real danger that its internal workings will be damaged, resulting in the need for a complete replacement unit. In many cases, the computer controlling the engine will sense that there is something wrong and will severely limit the engine’s performance in what is called a “limp-home” mode to prevent any further damage. You may also notice black smoke under acceleration, as unburnt fuel is ignited in the exhaust. VNT turbo cutawayThe problem may clear itself by cycling the ignition switch, but be warned that, having occurred once, it is extremely likely that the problem will reoccur and probably at the most inconvenient time. Until recently, the only solution was to buy a brand new replacement turbocharger, because the speed control mechanisms could only be calibrated at the factory. However, Turbo Technics can now clean the speed control mechanisms of many of these turbos and re-set them to the original factory calibration. As long as there is no other damage to the turbo, we should be able to get you back on the road at a fraction of the cost of a new turbo. As far as we know, we are the first and only turbocharger remanufacturer able to offer this service. If you have experienced these symptoms and have been told that you need a brand new turbocharger, then give us a call. Because of the potential savings, you may be pleased you did. Please contact our Sales Team to discuss your requirements in more detail.