Honda ASCORT valve leakage fault

       Symptom: ASCORT a Honda sedan, engine idling instability occurs, the exhaust pipe when accelerating phenomenon of black smoke; park and start driving, the need to continuously stepped on the accelerator pedal to start a few minutes; however, as long as the speed exceeds 1000r / min, the situation will improve acceleration.
       Maintenance process: after receiving the car, has been more repairman overhaul, almost the oil, the circuit all the parts and major components of the electronic control system are replaced with new parts, but the fault persists. Later, I found repeated test, after stopping at the start of the process, if the brake pedal to send a "hard", while other times the brake pedal is normal. This indicates a low degree of vacuum infineon tricore programmer after stopping intake manifold inside the start. Seize this phenomenon, first check to escape low vacuum manifold problems. First, in addition to clogging of the vacuum pressure sensor, all connected to a vacuum outside the vacuum channel, found not to be caused by leakage. Specially after passage of the EGR valve clogged, so the exhaust affect the intake manifold vacuum, but the fault is not eliminated.
       Repeatedly thought, only valve leakage is the crux of the maximum possible, but the test results, the cylinder pressure of each cylinder to achieve 1.25kPa, it is generally believed that the possibility of a small valve leak. Nevertheless, remove the check-valve cylinder head, especially the intake valve. After removing the cylinder head, it was found that 1,2,3-cylinder have an intake valve leak. When these Autel DS708 valves in the valve seat rotate, rotate very smoothly. Careful observation, found that these valve heads are slightly deformed. After the replacement, the fault disappears.
       Failure Analysis: engine has four valves per cylinder. Since 1,2,3-cylinder intake valve only a minor leak, so when the cylinder pressure is detected, if the operation of the starter is continuously driven crankshaft, cylinder pressure is not reduced. When the engine speed operation, valve leakage rate is very low, limited power down, the driver feel. At idle, the engine each cylinder charge less, due to valve leak, causing the engine running instability, but this time the engine per load. In the car started, the engine load increases, this time due to the low rate of movement of the valve, leak rate, so the engine has three cylinders due to poor working and power shortage.
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