In motion, the driver should always have the opportunity to increase speed. After all, in some critical situations it is necessary not to brake, but on the contrary, to accelerate sharply. But when this can not be done because the car does not gain speed, it is necessary to understand the causes of the problem. We tell you about the seven most common ones.
Why the car accelerates with difficulty
First, let’s deal with the physics of the process. Why does the engine does not gain speed? When idling or driving straight ahead, the load on the engine is minimal. Accordingly, if there are minor faults in the power or control circuits, the engine will run and the car will drive.
But when the driver wants to accelerate and presses the gas, it dramatically increases the load on the power unit. The portion of the fuel-air mixture increases, the revs should rise, but this may not happen. The whole point is that under load, any deviation of parameters from the norm plays a big role. Therefore, the faults that lead to the fact that the car slowly gains speed are not easy to find immediately after starting the machine: without load, they do not manifest themselves.
The engine is not warmed up properly
This, fortunately, is not a malfunction, but a nuance. And it is characteristic mainly for carbureted cars. While the engine is not warmed up, the vaporizability of fuel is low, and part of it on the way to the combustion chamber condenses on cold parts of the motor. Therefore, it is necessary to supply gasoline with reserve, i.e. to make the mixture richer. If this does not happen, the combustion efficiency will also be low, which will affect the traction characteristics of the motor.
In injector engines, the ECU selects the optimal fuel composition based on the coolant temperature sensor readings. And with a carburetor, the proportions have to be adjusted manually with the handle of the “suction cup” – it actually limits the entry of excess air into the motor. After all, with it the mixture will be depleted, and this is the reason why the engine does not develop speeds corresponding to the load, and the car can not accelerate.
Filters are clogged
The mixture that enters the engine is made up of air and fuel. Both are pre-filtered. If the filters are severely clogged, their throughput is noticeably reduced. As a result, one of the components may be missing. The ECU with such a deficit will not be able to create the right amount of mixture. As a result, the engine does not gain speed.
The manufacturer always prescribes filter replacement intervals, but these are only basic recommendations. For example, if you often drive on dusty roads in summer, the air filter will get dirty faster. Accordingly, and change it more often.
Worn or broken fuel pump
We have already written about the faults in which the engine starts and stalls even before starting to drive. They can also be the cause of the fact that the engine does not develop rpm corresponding to the load. If the pump is not able to provide the standard pressure, the injectors will not be able to inject the required amount of fuel during its opening time. As a result, the mixture will be depleted and the engine will not be able to develop full thrust. The pump often warns the driver about such a malfunction by increased noise coming from the fuel tank. By the way, the pump has its own filter – a mesh filter. It is also clogged, although it does not touch the bottom of the tank, where gasoline sediment can accumulate. So if the fuel pressure is insufficient, you should not immediately run for a new pump: first it is better to check the condition of the mesh.
The injectors are clogged
The injectors are responsible for fuel injection into the combustion chamber. We have already described their possible faults, but we will briefly repeat them again. In order for the mixture to burn completely, the fuel must be injected in the correct form and at the correct pressure. If the injector has a worn shutoff needle or clogged holes, it will not be able to inject the fuel properly. As a result, it will not burn completely, meaning the amount of energy released will be less. A typical complaint that the car does not gain speed well is often due to the poor condition of the injectors.
Loft in the throttle actuator
In older cars with a cable or rod throttle actuator, sometimes the throttle opens to a smaller angle than necessary when the gas pedal is pressed. There can be several reasons for this: for example, backlash in the pedal assembly or a cable stretched over time. However, there are also more trivial situations: you can find many stories on the Internet, when the movement of the pedal interfered with the rubber mat. If it is non-original, its edge or rib may get under the accelerator pedal and prevent it from being pressed all the way down.
An electronically controlled throttle may also not open properly due to wear or if it is very dirty and its flapper is jammed. In this case cleaning and diagnostics of the unit are required.
Sensors give incorrect readings
In electronic injection, the work of the ECU is based on the readings of sensors. Most of them are quite simple structurally, but still sometimes fail. And sometimes they work, but incorrectly.
Imagine that the coolant temperature sensor overestimates the temperature. Then, when the engine is still cold, the ECU will assume that it has already warmed up. And in the operating mode, as we wrote above, the mixture contains less fuel than immediately after starting. That is, the mixture is depleted. Then it is clear why the car slowly gains speed as it warms up.
The situation is similar with the mass air flow sensor (MAF). If the owner does not particularly care about the cleanliness of the air filter, mechanical particles can get into the sensor and over time either completely disable it, or lead to large errors in the readings. And from these readings directly depends on the composition of the mixture that is fed into the combustion chambers. So when the engine is poorly gaining speed, the problem may be in this element.
Finally, to the fact that the car is poorly gaining speed, can lead to the vagaries of the camshaft position sensor. The system of adjusting the timing phases is oriented on it, and if they are knocked down, the motor will work unevenly and not develop full power.
The piston group is worn out
The engine works by the energy of expanding gases during combustion. If the cylinder-piston group is badly worn, part of the gases burst into the crankcase and actually does not perform useful work. That is, the mixture is supplied in the right amount, but there is no effect – the engine does not develop rpm well. However, much more often the consequence of such wear is oil, abundantly burning in the combustion chamber and causing malfunctions in the valves and ignition system.
One of the most reliable ways to assess the condition of the engine is to measure the compression. True, for this you will have to get a compressometer or go to the service.
In situations when the car is gaining speed badly, the Check Engine icon often lights up. This makes it easier to find the fault: a diagnostic scanner will allow you to read the error code and narrow down the “circle of suspects”. It is also worth paying attention to external symptoms. For example, the appearance of blue smoke from the exhaust pipe indicates a bad condition of the engine, unstable operation of the power unit (they say: engine troit) is often due to failure or poor condition of one of the injectors, and noisy work at idle (“dieseling”) – problems with the phases of gas distribution. In any case, when contacting the service is better to name all abnormal deviations from normal engine operation.
Totals
- If the car is badly gaining speed, the reasons usually lie in an insufficient amount of mixture or its suboptimal composition.
- The most trivial cases in which this problem occurs – insufficient engine warm-up or clogged filters.
- Diagnostics is the easiest thing to do at the service – it is usually cheaper than trying to find the cause yourself “by poking and prodding”.
- If you’re going to the service, pay attention to the symptoms of poor engine speed.