Engine computer failure
    A BMW 525i sedan, driving weak and exhaust pipe a lot of white smoke, dashboard "CHECKENGINE" fault indicator light. Read the error code 1215, meaning the air flow meter or its line bad. After testing, the air flow meter impedance does not meet the requirements. Replace the air flow meter after the test, the situation slightly improved, but the fault remains the same. Check again and found that the 4th cylinder spark plug is covered with gasoline, indicating that the cylinder does not work. Infer the fuel injector has a problem, replace the nozzle after the test, no fault code appears, but the condition remains the same. With LED lights detection and found that the engine computer's fourth cylinder fuel injection signal output line no signal (good line), concluded that the computer is faulty. Replace the engine computer, troubleshooting.
    Engine start difficult
    A 6-cylinder BMW sedan, cold start difficult. Check the cold start control circuit, unplug the cold start nozzle and the heat timer switch on the plug, the ignition switch to the starting position, with the test lamp in the nozzle and switch STA wiring head to check the power supply situation. Plug the injector plug and connect the heat timer switch STJ directly with a wire. When the ignition switch to the start position, the engine started smoothly. Replace the light relay, troubleshooting.
    The engine is black smoke
    Example 1: a BMW sedan, the engine idling instability, black smoke, and fuel consumption. When the test even in the oil flavor, idling shaking, "CHECKENGINE" indicator light. Read the fault code 2, meaning the oxygen sensor "target = _blank> sensor circuit is poor or air / fuel mixture ratio is not correct. According to the following steps, installed in the exhaust pipe muffler front of the oxygen sensor to detect (using high impedance Digital multimeter):
    The road starts the engine and rises to the operating temperature
    Road ignition switch to "OFF"
    Road underneath the oxygen sensor connector "target = _blank" connector
    (Ie, the electromotive force of the oxygen sensor should be 0.1V ~ 0.9V), while measuring the plug voltage (ie, ECU pin set voltage should be 0.45V) measurement results show that the sensor signal voltage is 0V ( Normal voltage should be 0.1V ~ 0.9V), indicating that the sensor is damaged, so that the computer mistakenly received "thin" mixed gas signal, causing exhaust smoke. Replace the new pieces after troubleshooting.
    Example 2: a 12-cylinder 750i BMW sedan exhaust pipe black smoke, idle instability, accelerated to 1000 ~ 1500r / min exhaust pipe blasting, driving will intermittently enter the electronic control automatic transmission "failure protection" state, The LCD screen shows "TRANSPROGRAM" words, hanging into the D, 3, L file when the speed is not up, even if the throttle board can only be fully depressed at 800 ~ 1000r / min, driving sometimes turn off (but immediately But also start); hanging into the N, P file to accelerate good; engine failure lights sometimes lit, read the fault code for the poor mixture. In this regard, check:
    1, check the oxygen sensor signal voltage, idle when the left side of the oxygen sensor voltage is 0.1V ~ 0.9V (normal), the right side of the oxygen sensor 0.2V ~ 0.3V (mixture is too thin).
    2, the left and right side of the oxygen sensor and left and right air flow sensor replacement for the installation, the fault still exists.
    3, check the right engine fuel pressure, idle test results for the 274.6kPa (normal). The right side of the engine 6 nozzle cleaning, and then oxygen sensor voltage, still 0.2V ~ 0.3V.