Why the diesel engine does not start

Any owner of a car with a diesel engine may face the instability of its work. The engine either simply does not start, or instantly stalls. Sometimes it just works unstable, what makes you nervous. And there can be a lot of reasons for such behavior, and it is almost impossible for an inexperienced car owner to eliminate them on their own. But, if there is a little bit of knowledge, then you can try to adjust the mechanism yourself. For this you need to study the features of diesel engines, because if the diesel engine does not start, the reasons are quite difficult to identify and eliminate without at least theoretical knowledge.


  • 1 The principle of operation of diesel engines
  • 2 What damage and defects may occur
    • 2.1 Compression in engine cylinders
    • 2.2 Problems with glow plugs
    • 2.3 Breakdown of the fuel system
    • 2.4 Do not start in frost
    • 2.5 Other faults

The principle of operation of diesel engines

why the diesel engine does not start

Diesel engine may not start due to low compression

The difference with petrol engines is that the fuel is supplied to the combustion chambers separately from the air. If we recall the principle of operation of a gasoline engine (it does not matter with a carburetor or an injector), in it gasoline is first mixed with air, and only after this mixture is fed into the combustion chambers. In the case of a diesel engine, everything is different - first, air enters the cylinder, is compressed and heated, after which the fuel enters, which is ignited by the influence of hot air.

Diesel fuel enters the combustion chambers through nozzles. These elements of the fuel system are capable of spraying fuel to a state of fog. Due to this, diesel fuel is distributed evenly in the combustion chamber, therefore, it will also burn. The first seconds of operation, the combustion chamber is additionally heated by special glow plugs. They are necessary to increase the temperature of the air in the cylinders. Candles are very useful in the winter cold.

But it is possible to start the motor, even if the glow plugs failed or the relay controlling them failed. Candles are not a “vital” element, they only improve engine starting. In most cars, they turn off after a few seconds after the engine was started. However, on some models, they continue to work until the coolant temperature rises to the working value.

glow plugs for diesel engine

In the cold season, the diesel engine may not start because of problems with the glow plugs

What damage and defects may occur

Compression in engine cylinders

Compression fell and the engine can not start. For diesel engines, the pressure in the cylinders plays a key role - it is thanks to him that the air is heated. And if compression has fallen, the air does not heat up to a high temperature (about 800 degrees), therefore, the incoming fuel will not be able to ignite. If the compression in the cylinders fell critical, then most likely you will have to do a major overhaul. It also happens that the pressure drops in one or two cylinders. In this case, the motor starts, but it is unstable, there are vibrations. Of course, work in this mode is unacceptable, since the wear of the entire engine occurs much faster.

See also: Why the engine does not develop speed: possible causes

Problems with glow plugs

You can not immediately identify such a failure - it is invisible on a warm engine. In the warm season it is also almost impossible to calculate. But with the onset of cold weather, the whole picture changes and the engine may not start if the spark plugs are faulty. As already mentioned, they are necessary only to warm up the working part of the combustion chamber to a certain temperature. When two or more candles fail, you will almost certainly not be able to start the engine. The problem can be not only in candles - it is worth checking the relay and the control unit of candles. If the items are intact, you will hear clicks when you try to start the engine. In the case when the engine you choked recently and he did not have time to cool down, then, most likely, it will start successfully. But if the temperature on the street is low, then problems with the candles or their control system will not allow to do this.

Breakdown of the fuel system

check diesel injectors

It is best to check the nozzles on a special stand.

The entry of small particles into the injectors may be the reason why the diesel engine does not start. But immediately pay attention to whether there is a gray smoke from the exhaust pipe when trying to start the engine. Its presence directly indicates that the fuel supply to the combustion chambers is carried out in full, only the mixture does not ignite. Therefore, you need to look either candles or check compression in the cylinders. If the problem is associated with a decrease in compression, pour engine oil into each cylinder. For some time this way you can increase the compression. But after volatilizing the oil from the cylinders, the problem will reappear.

To make sure that the nozzles are clean, they will need to be unscrewed. And they need to be checked only on a special stand. Sometimes the nozzles are clogged partially, with the result that when you try to start the engine, it begins to sneeze, from time to time making attempts, it almost starts, but then it stalls. From the exhaust pipe will begin to pour black smoke. In other words, only a small part of the fuel that has entered the chamber is burned. Most are thrown into the exhaust system. If, however, when cranking the crankshaft with the starter, there is no even a hint of setting, and there is no smoke from the pipe, then it can be judged that diesel fuel does not reach the injectors. We'll have to arm ourselves with the tools and knowledge, check the entire fuel system starting from the tank and ending with the pump with injectors. But first, see if the pump drive belt is intact. Often it breaks or just flies.

See also: How to repair a silencer without welding with tape

Do not start in the cold

A very common problem is fuel waxing. As a result, diesel fuel becomes thick, like jelly. Of course, it does not pass through the filter and is not fed into the system any further. Therefore, in the cold season, use special diesel fuel for the cold season.

waxing of diesel fuel

Waxing of fuel may occur when using summer fuel in winter.

Other faults

Frequent faults in the fuel line. Sometimes cracks or leaks are created at joints. The main thing to remember is an important detail: if, when trying to start the engine, there is smoke (of any color) from the pipe, diesel fuel enters the combustion chambers, which means that the problem is most likely not in the fuel supply system. If there is no smoke, then you need to look for faults in the candles or cylinders (compression). Although the problem may be with the starter - it is faulty and can not crank the crankshaft.