Engine flameout failure occurs when the brake pedal is pressed.

Phenomenon: When the brake pedal is depressed, the braking effect is not good, and at the same time, the engine vibrates violently for a few times and then turns off, and the vehicle loses control and continues to slide forward.

Analysis:

1. If braking flameout occurs for manual transmission vehicles, consider whether it is a normal phenomenon of braking flameout with gears.

2. Braking is equivalent to releasing the accelerator pedal in a sense, considering that the idle motor is stuck at a low position.

3. When the vacuum booster is braked, there is vacuum air leakage.

4. Because the car is automatic, the flameout of the brake with gear is not considered.

5, detect no fault code

6. After investigation, the idle speed of the engine is stable at about 850 rpm, which meets the normal requirements. It shows that the non-idle motor is stuck in the low position.

7. When you step on the brake pedal at idle speed, the engine will turn off after shaking violently for a few times, and at the same time, the pedal will feel hard, which can only be caused by vacuum leakage. However, due to the normal operation of the engine at idle speed and normal driving, the vacuum pipeline connecting the vacuum booster with the intake manifold is not considered, and the fault is locked on the vacuum booster.

8. Connect the vacuum gauge to the intake manifold for testing. At idle speed, the vacuum degree is 64Kpa. At the moment when the brake pedal is pressed (the engine starts to shake, but it doesn't turn off), the vacuum degree drops to 15Kpa. Because of the large change, only the booster can have such a large air leakage in the intake system (the vacuum tube is very thick). Troubleshooting after replacement.

Diagnosis:

The left and right air chambers in the vacuum booster can't be well sealed during braking, which leads to a large amount of air entering the left air chamber and then entering the combustion chamber through the one-way valve and vacuum pipe. Because the car uses an air flowmeter, it can't sense the air intake behind the throttle valve, which leads to the mixture being too thin and flameout.