Symptoms
Sudden power drop, when accelerating, the engine power drops significantly. The engine goes into emergency operation mode. After restarting, the fault is "cleared" (to the next acceleration maneuver).
Cause – boost pressure too high or too low due to incorrect tuning
Using the intake manifold pressure sensor, the engine control unit detects too high or too low boost pressure and - before the boost pressure control valve adjusts the pressure – goes into emergency operation mode (motor protection function) and drastically reduces the size of the injected fuel doses. At the same time, it is saved in the fault memory: "Boost pressure (or intake manifold pressure) – control limit exceeded / not exceeded ". This entry remains in memory even after restarting the engine.
Troubleshooting and fault elimination
Fault "control limit exceeded" (i.e.. boost pressure too high) may be stored in the fault memory for other reasons as well, e.g. when the blades of the turbines are hard to move or if they are jammed (turbocharger with variable turbine geometry). You should then pull the vacuum hose from the pneumatic actuator stub of the turbine blade adjustment mechanism and connect the manual vacuum pump. Observe any negative pressure build-up, that the mechanism rod moves smoothly, no vibration. In the case of turbochargers with a blade adjustment mechanism built into the turbocharger body, in order to check the smooth movement of the adjustment mechanism, need to remove the turbocharger. If the mechanism is jammed or caught in something, most often the exhaust manifold with the compensator has to be removed. Only then can it be definitively stated, if the collector and the compensator are not e.g.. The rust particles corroded on the inside and entrained by the exhaust gas stream reach the turbine wheel. If that's so, over time, the turbine blade setting mechanism breaks down. To exclude the possibility of further damage to the mechanism after repair, the turbocharger and exhaust manifold should be replaced immediately.
Another cause of too much boost pressure may be an increase in engine power (excessive or unprofessional) via the driver. During the so-called. chip tuning are "awake" undoubtedly existing, but still slumbering, power potentials of modern direct injection engines. This is done by "adjusting" the boost pressure and the quantity of the dose per stroke. Probably the reason for this "pressure jump" and the symptoms described is the interaction of various errors. If you don't know, whether the increase in power was actually effected, this certainty can be achieved with several measured values. Calculated by the controller for a given control speed and load, the amount of injected fuel doses (in mg / stroke) should not exceed the values required by the manufacturer. In addition to the misfiring, The increase in power can also result in high fuel consumption, often black smoke or jerks in certain speed and load ranges.
If the fault memory contains "control limits not exceeded", it is very likely, that the actuator of the turbine blade setting mechanism is not subject to negative pressure at all or it is too low. In this case, the most common reason for this is not the boost pressure regulating valve itself, but kinked vacuum lines or broken fittings. To check, connect a manual vacuum pump and a pressure gauge and check the tightness of the entire vacuum circuit. If all wires are ok, check the diaphragm of the pneumatic actuator. Finally, check, that all vacuum lines are connected to the correct nozzles.
If, as a result of these checks, no irregularities or damage are found, this should be assumed, that the kinks of the wires occur during changes in the engine load, e.g. on the bulkhead or front bodywork. In this case, arrange the cables in this way, that the displacement of the engine relative to the body does not cause kinks in the vacuum pipes.
We also perform a quick test of all vacuum lines with a hand vacuum pump connected to the boost pressure regulation line. The negative pressure should last for some time. If this is not the case, to check, There are no leaks in the lines or their connections. The reason for this type of damage is the savings introduced by the manufacturer; during engine movements – caused by load changes – too short, thus, the stressed vacuum lines rub against the engine casing.