Failure phenomenon: a 2008 annual Porsche Cayenne (Cayenne) sedan, equipped with M5501 V6 engine, mileage 20000 km, users complained that the car cool car idle instability. Especially in the winter, cool morning start the car engine shake is very obvious, after running 30 s chattering away.
Check Analysis: phenomena and temperature due to a fault, the signal is first examined by conventional coolant temperature and the intake air temperature sensor, the measured values are consistent with the ambient temperature. Check the air intake system, there is no obvious leaks. Detecting an engine control unit, no fault code, but found to have a cylinder or multi-cylinder misfire phenomenon read the actual value. So cleaning the throttle and ignition system checked and found no anomalies. Measuring the cylinder pressure, leakage rates are within the normal range. After finishing the diagnosis of ideas, we will focus on the inspection of the fuel system. This car uses fuel injection technology, there are three fuel pumps, are two low-pressure fuel pump and a high pressure fuel pump. Measuring fuel gauge using a low-pressure fuel system, engine operation can be achieved when 0.55 MPa, which belong to normal, the vehicle is off the fuel pressure can be maintained within the normal range. Read the high-pressure fuel in the control unit the actual value of the engine sensed found under different conditions, the high-pressure fuel pressure variations in the engine 4 ~ 12 MPa, which is normal. Injector using endoscopy found no leaks, but found obvious soot cylinder, thus determining the fault caused by excessive carbon deposition.
Troubleshooting: After the inner cylinder coke clear the fault phenomenon completely disappeared. Return visit was made after a period of time, users reflect all normal.
reviewed: which engine with direct injection technology, the control unit of the fuel injection amount strictly controlled, since more coke cylinder, part of injected fuel and air mixture is not adsorbed, induced engine misfire. Currently Porsche Porsche has recommended that users specify the fuel additive to solve such problems.
(Wu added)