The Reasons Why A Car Stops Under Braking

Spontaneous stopping of a car’s unit-power plant can cause not very pleasant consequences, especially if the car stalls when braking while moving.

The functioning of a number of systems used to control the car depends on the operation of the power unit, and after it stops, the ability to control the behavior of the car by the driver deteriorates significantly, and accordingly, the likelihood of an emergency situation increases.

If the car stalls, when braking the driver not only cannot accelerate to make a maneuver, the hydraulic booster (if the vehicle is equipped with it) and the brake booster also stop functioning.

At the same time, the control and braking systems of the car themselves remain operational (that is, the control, in general, is preserved), but much more effort is needed to activate them.

The driver does not always have time to adapt to the new operating conditions of the car’s control mechanisms when the engine is not running, as a result, he is lost, which often becomes the cause of an emergency.

Some theory that is important to know

Situations when a car stalls when braking happens quite often and it does not depend on the brand of the car.

Two conditions contribute to the occurrence of such a situation – the transition of the engine to minimum speed (since the gas pedal is released) and the creation of an additional load on it – the brakes, slowing down the wheels, also create a force on the transmission elements, and, accordingly, on the power unit.

Despite the fact that the driver stops acting on the accelerator, the power supply system (injection, carburetor) continues to perform its function – it prepares the air-fuel mixture in the required proportions and quantities, and then feeds it into the cylinders, due to which the engine functions under the above conditions – minimum rpm and load from the use of the brakes.

But if the proportions of the combustible mixture are violated – it is “depleted” or “enriched”, then the engine simply cannot work on it.

As a result, the main reason why the car stalls when braking is the inadequacy of the air-fuel mixture to the working conditions.

Where to look for the reason?

Such a situation may arise due to problems in the functioning of a number of auto systems:

  • braking system;
  • intake and injection (power supply – for carburetor models);
  • electronic engine management system (injection version).

There are also other malfunctions that can lead to this problem, but they are quite rare. Therefore, you should first look for the reasons in the above points.

Vacuum booster and its pipeline

The brake system itself does not interact with the engine, therefore it remains operational after stopping the latter. But it has one component associated with the power unit – a vacuum amplifier, which can also have malfunctions.

And despite the fact that the amplifier is combined with the motor by a relatively insignificant part – a rubber pipeline, its malfunction can affect the proportions of the mixture supplied to the cylinders.

Let’s consider the simplified operation of the amplifier. It consists of two chambers separated by a membrane. One of these chambers (vacuum) is connected by a pipe to the intake manifold, through which air is drawn into the cylinders by pistons (they also draw it out of the amplifier chamber, so a vacuum is created in it).

When braking, the driver, acting on the pedal, opens a special valve that connects the second chamber to the atmosphere, thereby creating a pressure drop in the amplifier, which creates an additional effect on the master brake cylinder – less effort is needed to brake.

If the membrane is damaged, not only the performance of this unit will deteriorate. The air entering through the valve will seep into the second chamber (vacuum), and from it will enter the intake manifold – there will be a violation of the proportions of the combustible mixture (its “depletion” will occur), which causes the car to stall.

The same situation occurs when the pipeline connecting the brake booster to the manifold is damaged, but there is one caveat – air is constantly leaking through the crack.

At medium and high revs, the excess amount of air has a slight effect on the proportions of the mixture, so the problem is invisible, it manifests itself only at low revs and with an additional load on the motor. And since, under such conditions, the amount of the mixture is already small, the excess air leads to the engine stop.

A malfunction of the vacuum booster and its piping is the most common reason that the car stalls when braking. But it is not difficult to identify a breakdown.

Checking the vacuum brake booster and tube integrity

To determine the operability of the vacuum brake booster, you just need to:

  • Start the engine (so that it creates a vacuum in the device);
  • Mute;
  • “Pump up” the brakes (press the pedal a couple of times all the way). In this case, the amplifier will cease to perform its function and the resistance on the pedal will increase – after a couple of strokes it will not be possible to squeeze it out completely;
  • Keeping the pedal depressed, start the engine.

If, after these actions, the resistance on the pedal disappears, and it easily goes all the way, then the unit is fully operational and the reason for the motor stops during braking lies in other units. You can also check it by acting in the opposite direction – on the clamped brake pedal after stopping the unit, resistance to the force of the foot will gradually begin to increase, which will indicate the serviceability of the amplifier. Checking the pipeline is also easy:

  • Disconnect the tube from the amplifier;
  • Start the car;
  • Use your finger to block the hole in the tube, open it;
  • Monitor the behavior of the power plant.

If the tube is not damaged, then after closing the hole, the engine speed should increase, and when released, fall (unstable engine operation is possible).

When the behavior of the unit when closing and opening the pipeline openings does not change, this indicates the presence of air leaks.

Often it is possible to identify a malfunction of the amplifier and its connecting tube by the characteristic hiss due to air leaks.

If we consider a separate case with an amplifier, then such a sound can be heard in the cabin, after pressing the brake pedal. But the hiss in the pipeline is heard only when the hood is open.

The indicated problems are solved only by replacing damaged or faulty components since they are not repairable.

The reason is in the injection system

The car can stall during braking also due to problems in the injection system (injector) or power supply (carburetor). But unlike the braking system, they do not affect the amount of air, but the fuel.

In injection cars, the problem with the spontaneous stopping of the engine occurs due to malfunctions:

  • Fuel pump;
  • Filters;
  • Injectors.

The general reason for the occurrence of such a problem lies in the following – the ECM that controls the fuel injection, after releasing the gas pedal, stops the operation of the gas pump so as not to create an excess of pressure in the fuel lines.

After pressing the pedal, the functioning of the pump is restored. Such a feature of the work can cause the motor to stop spontaneously.

The wear of the fuel pump leads to a decrease in its performance. As a result, after being put into operation, it is not able to quickly provide the system with the required amount of fuel (it takes time to pump it in and bring the pressure in the fuel rail to a level).

During this interval, the combustible mixture is “depleted” due to lack of fuel, the car stalls. The same situation occurs due to severe clogging of the fuel filters (coarse or fine cleaning). Due to dirt, the throughput of the filters drops, as a result, the pump takes time to “push” the right amount of fuel through them. The same period of time arises when the mixture is “depleted”.

Worn or clogged nozzles act differently. Due to such problems, the closing speed of the injectors decreases, and when the speed is reduced, they supply more fuel than required – the mixture “over-enriched” occurs, which also leads to a spontaneous stop of the engine, and then the machine when braking.

The efficiency of the injection is carried out by measuring the pressure in the lines and the fuel rail. Inconsistency of this parameter indicates a pump malfunction or severe clogging of filters.

The injectors are diagnosed on special stands, most likely they will need to be cleaned or replaced.

Carburetor and fuel pump

Pump On carburetor engines, two components affect the fuel-air mixture – the fuel pump and the carburetor.

Motors with this power supply use a mechanical vacuum pump. If a membrane rupture occurs in it, then the unit simply will not be able to pump the required amount of fuel.

If the membrane is severely damaged, the pump completely stops flowing, but if the gust is insignificant, then this will affect its performance.

At high speeds, the amount of pumped fuel may be quite enough for the normal operation of the engine, but at low speeds, there will be not enough gasoline (the same “lean” mixture occurs).

The carburetor can cause the machine to stop spontaneously when braking due to:

  • Incorrect adjustment of idle speed (XX);
  • Clogging of XX system channels;
  • Malfunction of the XX solenoid valve;
  • Air leaks at the junction of the carburetor with the intake manifold.

For the most part, the “fault” of a stalled car during braking is problems in the operation of the idle system, and they can be solved by thoroughly flushing the carburetor, checking and replacing the solenoid valve.

Malfunction of the intake system

In injection cars, the engine can stall during braking and due to malfunctions in the intake system, which is responsible for supplying air to the cylinders and dosing it.

The main element here is the throttle unit, which, by opening and closing the damper, regulates the amount of air supplied, it is on this damper that the driver acts by pressing the gas pedal.

In the design of the throttle assembly, an idle channel is provided, which ensures its supply to the intake manifold when the damper is closed.

If this channel gets clogged, then there will not be enough air for stable operation of the motor at XX – “over-enrichment” of the mixture will occur, which, in combination with the additional load due to braking, will cause the machine to stop. This problem is solved by cleaning the throttle valve and the assembly as a whole.

Electronic Component

Electronics can also affect the proportion of the combustible mixture. Here, the computer and the idle speed regulator can cause the machine to stop during braking.

The ECM is responsible for the functioning of all engine systems, and if a malfunction occurs in it, this will certainly affect its performance.

One of the breakdowns of this unit may be incorrect processing of signals from sensors and a change in the operation of actuators.

If it is simpler, the ECM will incorrectly calculate the amount of fuel supplied to the engine cylinders at XX, and the mixture will be “lean” or “enriched”.

Regarding the governor, this assembly adjusts the position of the throttle valve depending on the operating conditions of the engine. And if the regulator is faulty, then it will affect the amount of air supplied, which will lead to a violation of the proportions of the combustible mixture.

It is impossible to check electronic components without special equipment, but it is possible to replace them with known good ones in order to determine which unit is malfunctioning, leading to the spontaneous stop of the machine when braking.

In the process of searching for the cause, it will not be superfluous to check the elements of the ignition system – candles, high voltage wires. Malfunctions of candles and breakdowns of high-voltage wires lead to interruptions in the operation of the motor, which can not always be detected at medium and high speeds, but at low, and even under load, such problems can easily lead to engine shutdown.

A sequential check of all the specified components of the car will certainly lead to the reason due to which the car stalls when braking.

You just need to start looking for the causes of the malfunction on the basis of the principle “from simple to complex.” There is no need to look for the cause in the operation of the ECM if the air is poisoned by the hose of the vacuum amplifier.

About the author

Melisa Marzett provides custom writing help for more than 5 years now and enjoys her job. She is much of a reader, a traveler, and an observer. She is a life enthusiast who tries to spend each and every day as if it was the last one.

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