A 2005 Shanghai GM Chevrolet Sail cars, mileage 8000km. According to the owners reflect the car driving the engine sometimes flameout, check to the repair station is the fuel pump fuse blows, the fuse before the fuse without any aura, when the fuse blows to hear a relatively large "right" sound. After replacing the fuse, the fuse will be blown after a few minutes. Several times to repair the car repair station, replaced the engine wiring harness, instrument harness, oxygen sensor, ignition coil, fuel tank and a number of fuel pumps and other components, but did not find the root cause of the malfunction. Take over the car, the maintenance staff based on the previous maintenance records can be identified as a typical intermittent fault failure, if not conduct a comprehensive inspection and analysis, experience and blind replacement parts alone difficult to solve the problem. A common cause of a blown fuse F26 is that there is a short circuit in the fuse-related circuitry, or there may be a fault in the fuel system, such as a fault in the fuel evaporating system that creates a negative pressure in the fuel tank or a fuel line that is clogged with fuel Of course, this is not the case when the pump load is increased, which increases the operating current of the fuel pump and blows the fuse. First check the blown fuse F26, the capacity of 25A, the fuse cross section of the black dots, indicating that the fuse is immediately blown. If the fuse is slowly blown, there are no black dots on the fuse's cross-section, and the ends of the breakpoint should be sharp. It can be seen from the related circuit diagram that the fuse F26 supplies power to the oxygen sensor, the ignition coil and the fuel pump relay. If the lines of the three power consuming appliances have a short circuit, the F26 fuse will be blown. In order to determine whether the line is faulty, I decided to check whether there is a short circuit in the line powered by the F26 fuse. The author respectively in the oxygen sensor heating power line, the ignition coil power line, the fuel pump plug power line near the location of the electrical equipment in series with 25A fuse, and install the fuel pressure gauge, with a rubber stick to the fuel pressure gauge sticky In the windshield on the right, so that the road test observed. During the road test, I found that the value of the fuel pressure gauge is getting lower and lower, and then the engine is turned off. The fuses in series are checked and the fuses connected in the fuel pump circuit are found to be blown. As the fuse is near the fuel pump plug, there is a problem with the fuel pump. Remove the rear seat under the fuel pump inspection and found that the fuel pump sliding cover bracket has the top of the pump plastic stopper top bad, and the pump inside the wiring harness squeeze damage signs. Why does this happen? Check the fuel tank and found that the fuel tank has been deflated deflated and severely deformed, which should be caused by the vacuum inside the fuel tank is too large. What causes the vacuum inside the fuel tank is too large? The fuel tank of the Sail car is a plastic fuel tank, the fuel tank cap does not have the ventilation function, the pressure inside the fuel tank is mainly regulated by a fuel evaporative emission control system (EVAP), and the fuel evaporative emission control system mainly consists of a buffer activated carbon canister, Valve and fuel evaporative control (anti-roll valve, shut-off / shut-off valve). Normally, the internal pressure of the fuel tank is about 0.3 kPa. When the internal pressure of the fuel tank is under 3.6 kPa, the fuel vapor can enter the activated carbon canister from the shut-off / shut-off valve. When the internal pressure of the fuel tank is about -3.5 kPa Fresh air from the outside can enter the fuel tank through the blocker / shutoff valve to maintain the pressure balance in the fuel tank. The shutoff / shutoff valve and the anti-roll valve separately placed on the top of the fuel tank work together to adjust the pressure inside the tank. If the activated carbon canister is clogged, the anti-roll-over valve on the top of the tank, or the blocking / closing valve stuck in the closed position, or if the connecting line between them is clogged, can cause the vacuum inside the fuel tank to deflate excessively to compress the fuel Pump bracket, damaging the fuel pump and shorting the fuel pump circuit. Because the car had been replaced with a fuel tank assembly (including shut-off valves and anti-roll valves) in previous repairs, the activated carbon canister was not replaced. Remove the activated carbon cans, blow back and forth with the mouth of the three activated carbon cans on the breathable tube, feeling a greater internal resistance. When the vehicle is driving on the bumpy road, I think that the activated carbon inside the activated carbon can swing back and forth on the carbon can be blocked when the intake cans, resulting in negative pressure on the fuel tank. Replacement of activated carbon canister, repeated road test and follow-up visit, the fault never occurred.
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