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Diagnose Faults Through Exhaust Gas Color

Everyone likes colorful things, but not all colorful things are good. For example, we all know that in the wild, mushrooms with very bright colors are basically poisonous mushrooms. If eaten by mistake, they will be food poisoning and even life-threatening. The same is true of the vehicle’s exhaust. The appearance of different colors means that the vehicle has been “sick”, so you should take it to see the “doctor”. Different colors of tail gas have different diseases. Generally, there are three colors: black, blue and white. What do they reflect respectively?

exhaust-color

Black exhaust gas

  • Fault phenomenon: when the truck is running, the engine exhaust pipe emits black smoke with abnormal noise.
  • Fault cause: the main reason for black smoke from the exhaust pipe is that the mixture is too rich and the combustion is incomplete. It may be that the automobile engine is overloaded, the cylinder pressure is insufficient, the engine temperature is too low, the air filter element is blocked, individual cylinders do not work and the ignition is too late.

Troubleshooting:

1. If a large amount of black smoke is emitted from the exhaust pipe of the engine and accompanied by the sound of gunfire, it can be concluded that the mixture is too rich. Or because the injection time is too early, the injection timing should be readjusted; If the air filter is blocked, clean or replace it.

2. If a small amount of black smoke is emitted from the exhaust pipe of the engine and accompanied by a rhythmic “sudden” sound, it can be concluded that it is caused by the non operation of a few cylinders or the inaccurate ignition timing. The cylinder by cylinder fire cut-off method can be used to find out the inoperative cylinder, or check and correct the ignition timing.

exhaust-color-

Blue exhaust gas

There are two situations when the exhaust pipe discharges blue smoke (in fact, the blue smoke we see is light refraction of cyan smoke and gray smoke). We should pay attention to distinguishing.

  • Fault phenomenon 1: blue smoke or grey smoke is discharged from the exhaust pipe, and a burnt smell is smelled.
  • Fault cause: the exhaust pipe emits blue smoke or gray smoke when the engine is running, mainly because the oil enters the cylinder combustion chamber to participate in combustion. The oil consumption will increase, mostly because the oil rushes into the combustion chamber. When the oil enters the cylinder and evaporates into blue after heating, the oil and gas are discharged out of the cylinder together with the exhaust gas, and the blue flue gas will be seen at the exhaust pipe orifice.

The main reasons for oil entering the cylinder are:

  1. The cylinder is worn or the piston ring is poorly sealed, causing the crankcase oil to enter the combustion chamber.
  2. The oil level of the oil pan is too high or the oil pressure is too high so that too much oil adheres to the cylinder wall.
  3. The valve and valve guide are worn so that the fitting clearance is too large, and the oil is sucked into the combustion chamber.
  4. The oil level of the air filter is too high or the filter element is seriously blocked so that the oil is sucked into the combustion chamber.
  • Fault phenomenon 2: exhaust pipe exhausts blue smoke
  • Fault cause: because the oil is not good, if the performance index of diesel fails to meet the requirements, the engine exhaust will emit blue smoke later.

Troubleshooting:

Troubleshooting of phenomenon 1

  • If the engine has been used for a long time or has reached the specified overhaul mileage and the engine power is insufficient, the main reason is that the piston and piston ring are seriously worn and the oil jumps up due to poor sealing, so it should be sent to the automobile repair shop for an overhaul.
  • Check whether the oil level of the oil dipstick is too high; Check whether the clearance between the cylinder and the piston is too large, whether the piston ring is installed reversely, whether the oil flows into the mixture, the inlet valve guide is worn or the sealing ring is damaged, the oil is sucked into the cylinder, and the cylinder gasket near the oil passage of the engine body facing the cylinder head is ablated. Repair it if necessary.

Troubleshooting of phenomenon 2

  • you need to go to a regular gas station to refuel.
exhaust color

White exhaust gas

  • Fault phenomenon: a large amount of white smoke is discharged from the exhaust pipe. One is milky white, the other is vapor white smoke, and there are water droplets at the outlet of the exhaust pipe.
  • Fault cause: a large amount of white smoke is discharged from the air pipe. There are two situations:
  1. Milky white oil mist is discharged from the exhaust pipe. The main reason is the poor vaporization of fuel, which is discharged from the exhaust pipe without combustion, resulting in milky white smoke. It is common to start the engine in winter because of low temperature and poor fuel atomization. It usually disappears with the increase of engine temperature after the engine is started.
  2. A large amount of water vapor and white smoke are discharged from the exhaust pipe, and there are water droplets at the outlet of the exhaust pipe. The main reason is that the coolant jumps into the cylinder or the water vapor formed by water in gasoline.

Troubleshooting:

  1. When a truck parked in the winter or rainy season is started for the first time, white smoke can often be seen. It doesn’t matter. Once the engine temperature rises, the white smoke will disappear. There is no need to repair this condition. If the exhaust pipe becomes black smoke after the engine temperature rises, it indicates that the cylinder pressure is too low or individual cylinders do not work, which should be checked and eliminated.
  2. When the engine is running, a large amount of water vapor and white smoke are discharged from the exhaust pipe. Check whether there is water in the oil tank, whether the cylinder gasket is damaged, whether the cylinder block is cracked, whether the cylinder liner sealing ring is good, etc.
Postscript:

Observe the tail gas of your truck more, find the disease from its color earlier, and apply the medicine to the case earlier. You will love your truck less – it’s not too late to mend it. Here, I would also like to remind you that doing a good job of engine maintenance can reduce the probability of “color exhaust”. more preventive inspections.

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