Symptom: a chassis for the E39 BMW 530i sedan, there are hot and cold cars are not good start phenomenon, which is particularly cold when the phenomenon, generally have to start four to five times.
    Fault diagnosis and troubleshooting: According to the phenomenon of the car analysis, in the first easy after the start, starting from the basic start, from the oil. Gas Road. Machinery. Circuit and other four aspects to consider, can cause the failure of the reasons are generally the following (3) the fuel pressure is too low; (4) the idle control valve and its lines are faulty; (5) the cylinder compression pressure is too low (2) the air flow meter is faulty; (6) the ignition timing is not correct; (8) the water temperature sensor several lines of its fault.However, the car at the start, with carburetor cleaning agent to the intake system jet, start the car situation will be better. (5) (6) and (7), then connected to the fuel pressure gauge test oil pressure, it is not expected, the oil pressure is low, the inspection found in the oil pressure gauge, The car near the petrol filter device at a tubing collapsed, and the tubing is just into the tubing.With the driver agreed to replace the tube, the hot car started to improve the phenomenon, but the cold phenomenon is still in. After the start check the engine intake The system does not leak, hit the direction or air conditioning, the engine speed will increase, so you can exclude (1) and (4), in place Motive power, without any sense of abnormality.It is estimated that the air flow meter problem is not large, it seems the problem is likely to be out on the water temperature sensor and its line.Unit the engine inlet air cylinder wall temperature sensor, the sensor is Four-wire, find the water temperature signal two plugs. With a multimeter ohm stalls to measure its resistance, both in the cold or hot car when the resistance are only a dozen ohms, it seems the problem lies here. To a sliding rheostat to replace the water temperature sensor to simulate the water temperature signal.When the sliding rheostat slide to more than ten ohms, the engine is bad, so you can determine the water temperature sensor problems, replacement, troubleshooting.
    Fault analysis: From the above discussion, because the engine into the tubing was battered caused by hot start difficult, and the water temperature sensor damage is cold start difficult "culprit." The water temperature sensor is a negative temperature coefficient. Conditions, the engine needs a thick mixture, the engine injector in the basic fuel injection pulse width, but also need to add fuel injection pulse width, so that the mixture becomes thick, and the water temperature sensor is used to correct the fuel injection pulse width, When the water temperature is low, the resistance becomes larger, the engine computer detects this signal, automatically increase the fuel injection pulse width, to extend the fuel injection time, so that the mixture becomes thick, is conducive to the engine cold start, Fuel injection pulse width, and this car water temperature sensor is broken, the resistance has been in a dozen ohms, so the engine to determine this time do not need to enrich, but the actual car to start the case, so that caused the cold start difficult.