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A Lexus 3003. 0L car with a mileage of about 50 thousand km, equipped with 1 MZ-FE electronic controlled engine and automatic transmission. User response: the engine is difficult to start when the car is hot, and the starting machine can rotate continuously for 4 ~ 5S before it can drive the car. After receiving the car: to confirm the symptoms of the fault, the engine starts smoothly under the condition of cold car, the engine is difficult to start under the condition of the hot car, and the jitter is serious after the operation, and a lot of black smoke is taken out of the exhaust pipe. The engine went back to normal for a moment. Shut down the engine, start immediately, failure phenomenon does not appear; after 10min start, failure occurs. It is preliminarily determined that the cause of the failure is the pressure relief of the oil supply system. Connect fuel pressure gauge to measure fuel pressure during engine running, normal. When the engine is shut down, the fuel pressure drops quickly, and then drops to 100kPa after 5 min. Pinching the fuel supply between the fuel pressure gauge and the fuel filter, the pressure is still dropping rapidly. The injector was dismantled to test, and no anomaly was found. Remove the intake port, observe the valve, and find lots of black carbon deposits. The spark plugs are removed, and the electrode site is all carbon accumulation. The endoscope was extended to the cylinder and 4 oil injectors were found to be leaking. The engine is charcoal removed, all fuel injectors and spark plugs are replaced, and the failure symptoms disappear completely, and the maintenance work is finished. Why does the injector not leak while holding the pressure test on the instrument and leak on the vehicle? The main reason is that, although the injector pin valve parts wear, but the expansion coefficient of the valve seat and the valve core is different, the wear gap increases when the hot car is hot, and the fuel will overflow slowly from the gap and atomized in the intake pipe. When the vehicle is started again, the mixture in the cylinder is too thick to ignite. In the long run, a lot of Coke will be generated, which will seriously affect the engine performance.