There are so many reasons why a diesel engine smokes that it is often impossible to determine the fault without professional equipment. In the article we will reveal the symptoms of the main defects in the operation of injectors, the EGR system, as well as anomalies in the operation of sensors, due to which fuel consumption increases and black/blue smoke is observed after cold start-up and during acceleration.
Diesel smokes when cold
The appearance of gray smoke is a common attribute of cold starts for many owners of cars with a diesel engine. The cause of smoke in cold weather can be one or a combination of the following faults:
- Low compression. The air in the combustion chamber does not heat up enough, which is why the injected portion of fuel does not burn completely. The smokiness of a diesel engine is associated with a high content of unburned fuel vapors in the exhaust gases.
- Malfunction of the preheating system. Glow plugs are necessary not only for preheating the combustion chamber before starting, but also for better combustion of fuel in the first minutes of engine operation. The duration of their activation depends on the algorithm laid down by the designers, which takes into account the load on the engine, the temperature of the coolant, intake air, etc. If one or several glow plugs are faulty, the fuel in the corresponding cylinders will burn incompletely. In this case, not only gray smoke from the exhaust pipe is noticeable, but also uneven engine operation and increased vibration.
- Exhaust gas recirculation (EGR/AGR) system jamming. If the exhaust gas return valve does not close completely, the exhaust flows back into the intake manifold and displaces some of the fresh air charge. At the same time, the temperature in the combustion chamber decreases, resulting in smoke with a gray tint.
- Incorrect operation of fuel injectors. A significant deviation from the reference characteristics leads to an increased cyclic feed. A large portion of fuel does not burn completely, which leads to a high concentration of unburned diesel fuel in the exhaust gases.
- Injection angle too late. In systems with electronic control of the injection angle, a malfunction occurs due to incorrect installation of timing marks or a defect in the operation of the injection timing regulator. On a car with a mechanical injection pump or a high-pressure pump with a relatively simple mechatronic design, the injection angle is affected by the correct position of the injection pump gear relative to the crankshaft and camshaft.
- Defect in the operation of the mass air flow sensor, absolute pressure sensor in the intake manifold. If the sensor readings differ significantly from the actual mass of the fresh air charge, the cyclic supply will be calculated incorrectly, which can lead to overflow and poor combustion of fuel in the cylinders.
Application of anti-haze additives
Numerous chemical additives from different brands can reduce oil consumption. Their action is to form a protective film on the surface of rubbing parts. This film fills all microcracks on the surface, protecting the part from premature wear. The use of such additives replaces such a procedure as decoking of piston rings. But are chemicals really effective or is it all just marketing?
Anti-smoke additives
Experts on automotive forums express conflicting opinions about the use of special additives. Experienced auto mechanics are confident that regular use of chemicals leads to the appearance of a dense oil layer on the surface of parts, which is difficult to wash off. All this complicates engine overhaul, because many parts that cannot be cleaned have to be replaced. This significantly increases the cost of repairs.
The use of special additives for the motor
Important! Additives will only help to slightly extend the life of the engine, but they do not provide any guarantees for its trouble-free operation.
Anti-smoke - anti-smoke additive
Old school
It is worth making a digression and mentioning “old” school engines, whether swirl chamber or direct injection, on which environmental limiters in the form of a particulate filter, catalyst or USR system are not available from the factory or have been cut out/removed by the owners. If gray smoke with a bluish tint in the first minutes after starting the engine in cold weather does not appear in conjunction with poor starting, loss of dynamics, harsh and uneven operation, the owner should not worry.
Slightly decreased compression, deviations in cyclic flow due to wear of injectors, imperfect operation of individual sensors are a natural consequence of long years of operation and high mileage. The owner just needs to make sure that the thermostat, glow plugs, USR and idle speed increase system are in good condition, which are extremely important for quick engine warm-up and smooth operation after a cold start.
Why is black smoke dangerous when accelerating?
Diesel smokes black smoke in the case of an over-enriched mixture, when the air entering the cylinders is not enough for complete combustion of the injected portion of fuel. Often, thick black smoke is observed during sudden throttle changes, intense acceleration, or when driving under load. The main reasons for increased smoke:
- Insufficient air entering the intake manifold. A lack of oxygen can be caused by a clogged air filter, a leak in the intake tract, or a malfunction of the turbocharger.
- Excessive fuel supply. Most often, the cause of overflow lies in faulty injectors, but a similar situation is possible in the event of improper operation of the mass air flow sensor or absolute pressure sensor (DBP). If the sensor readings do not correspond to the actual amount of air entering the intake tract, the ECU (Engine Control Module) is not able to select the correct amount of fuel. The mixture turns out to be over-enriched, which is why black exhaust from the diesel engine is observed.
- Changing the timing and duration of fuel injection. The reason may be either faulty injectors or control. The timing of injection and the duration of the open state of the injectors can be affected by incorrect operation of the sensors that record the load on the engine (mass air flow sensor, DBP, gas pedal position sensor), as well as changes in the ECU firmware. When chip tuning, changes to the fuel map are made intentionally to increase the power of the diesel engine.
- EGR valve stuck in open position. Incomplete blocking of the exhaust gas return channel leads to a decrease in temperature in the combustion chamber. If the EGR valve does not close completely under full load, the air-fuel mixture does not burn completely and black smoke comes out of the pipe.
- Low quality diesel fuel.
- Incorrect installation of timing marks.
A general violation of the cyclic fuel supply or uneven fuel supply between the cylinders leads to increased loads on the parts of the cylinder-piston group, the crankshaft and its liners. Significant overflow can destroy the piston partitions and cause scuffing on the liners, which will subsequently lead to them turning over.
What does the white and bluish color of exhaust gases mean?
If a diesel engine emits blue smoke, the engine oil burns in the cylinders along with the fuel. Reasons for oil getting into the combustion chamber:
- turbocharger malfunction. Oil enters the intake tract through the turbine shaft seal;
In rare cases, blue smoke is associated with oil burning out of the exhaust pipe, where it enters through the turbine shaft seal in its “hot” part.
- wear of oil scraper rings. Piston rings are necessary to remove excess oil film from the cylinder walls. If the rings do not cope with their task, the oil remaining on the walls burns along with the air-fuel mixture;
- wear of valve seals. Seals are designed to seal the cylinder head cavity from the combustion chamber. Over time, due to frequent temperature changes, the rubber seals harden and begin to leak oil into the combustion chamber. Most often, in this case, smoke with a bluish tint appears after the car is idle and disappears a few minutes after starting the engine;
- increased pressure of crankcase gases. The reason is either wear of the cylinder-piston group, or improper operation of the crankcase ventilation system. Excessive pressure in the crankcase space prevents the normal operation of the oil scraper rings and the drainage of oil from the turbine.
Diesel smokes white smoke when it burns antifreeze in the cylinders. Ways it enters the combustion chamber:
- contact area between the cylinder head and the cylinder block. The reason may be corrosion of the cylinder head or a loose gasket. Antifreeze getting into the cylinders can be caused by deformation of the cylinder head/cylinder head mating planes (often due to engine overheating), installation of a poor-quality gasket, or non-compliance with the cylinder head installation rules;
- Cracked cylinder head or cylinder liner.
Video: The reason why diesel smokes when cold, which many people don’t know about, Ford Connect 1.8d, HCPA
Diagnostics and fault localization
To determine the cause of the engine smoking, it is not necessary to open it. The appearance of purple smoke until the engine has completely warmed up does not indicate serious defects. The problem is due to the fact that metal in a cold state has less volume than in a hot state. Because of this, oil gets into the gaps between the cylinders. After expansion during heating, the gaps narrow and the defect is leveled.
Blue smoke
Blue smoke from the engine, which intensifies after warming up, indicates wear of the piston group, which requires major repairs.
The presence of a problem is indicated by increased oil consumption not provided for by the factory. The car owner is recommended to constantly monitor its level in order to identify the initial appearance of the defect. It is especially important to carry out an inspection on modern cars. They are equipped with equipment that purifies exhaust gases to minimize environmental pollution, causing the color of the smoke to become transparent.
Some stations offer compression measurements to identify a defect, but the procedure is not always informative. Due to the pressure created by the oil in the cylinder-piston group, the value may correspond to the factory value or deviate slightly.
