Symptom: a BMW 750iV12 sedan acceleration bad.
    Maintenance process: the first failure verification, anxious step on the throttle, the engine speed is not with the foot; slow oil, speed up to 300ORPM after it is difficult to go up. With OB15 decoder for computer diagnosis, display normal, had to start from the basic inspection work:
    1. Measure the oil pressure, find the 1-6 cylinder petrol pump pressure is "0", and then measure the pump power and landing is good, indicating that the pump itself is a problem. 7-12 cylinder petrol pump pressure 3.Okg / cm2, unplug the oil regulator vacuum tube, oil pressure rose to 3.6kg / cm2, normal.
    2. Measure the intake manifold vacuum, fluctuate at 3000mmHg, the standard is 400-600mmHg, obviously this is not normal.
    3. Measure the cylinder pressure and found that 1,3,9,10 four cylinders pressure only 3-4kg / cm2, add a little oil, the pressure is more than l0kg / cm2, indicating that four cylinders have serious channeling gas phenomenon, The remaining eight cylinders had a pressure of between 9.0 and 10 kg / cm2.
    4. Check the spark plug, high pressure line, sub-fire and sub-fire cover are normal.
    5. Measure the primary and secondary resistance of the high-voltage coil, the primary resistance of the 1-6-cylinder high-voltage coil is 0.54Ω (0.5 ± 0.1Ω standard), the secondary resistance is 11.5KΩ (standard 6 ± lKΩ) This is not normal The 7-12 cylinder of the first and second resistance were 0.54Ω, 5.9KΩ, normal.
    6. Check the nozzle, the resistance is 15-17Ω, no leakage, fuel injection uniform, good mist, accordingly, we replaced the 14-cylinder petrol pump, 1-6 cylinder high-voltage coil, and the engine was Overhaul, accelerated with a significant improvement, but still did not solve the fundamental failure, mainly from the idling to 3000RPM between the normal, but to further refueling, the speed is difficult to go up with OB15 decoder for computer diagnosis, Repeat the basic inspection work, the two petrol pump pressure are 3.Okg / cm2, cylinder pressure are 10kg / cm2 or more, and the pressure difference between the cylinder is not more than 5%, the secondary voltage are between 12-13KV, are Normal, the intake manifold vacuum 380mmHg, is not normal, the standard is 400-600mmHg, then the engine computer 88 feet for signal voltage, power and landing test, no abnormalities, previously encountered a Mitsubishi The sports car went to 10Okm / h when there is no oil on the phenomenon, was found to be caused by exhaust pipe blockage caused by poor exhaust, so the same removal of the exhaust pipe, test miracle appeared, Good, and intake manifold vacuum High to 490mmHg. Finally, the exhaust pipe is forced open three-way catalytic converter, all were found to coke activator hole blocked, resulting in poor exhaust gas, after removing the activator replacing test, troubleshooting.