Before taking any measurements, increase the engine speed to 2500 rpm and maintain it for about 20 seconds. Then reset the speed to idle and watch the exhaust gases flow out of the exhaust pipe. If the idle speed is too high, or there is thick blue or distinctly black smoke coming out of the exhaust pipe for more than 5 seconds. - the engine does not meet the requirements. As follows from practice, blue smoke indicates oil burning (from valve stem seals, valve guides, piston rings or cylinder diameters), while black smoke indicates incomplete combustion of the fuel (dirty air filter element, too rich fuel mixture, or defective carburetor or fuel injection system).
If the idle speed and exhaust are satisfactory. then you need an exhaust gas analyzer that allows you to measure the content of carbon monoxide (SO) and unburned hydrocarbons (NS). The following paragraphs assume that such a device can be rented or borrowed, since it is not profitable to buy it for work at home. You can also use the services of the nearest station to check the composition of gases for a small fee.
CO emission
Existing ILO regulations limit the amount of CO in exhaust gases when the engine is idling to 4.5% for vehicles after August 1983. The CO level set by the manufacturer is within these limits.
If the CO content cannot be reduced enough to pass the test (provided that the fuel system and the ignition system are in good condition), it can be assumed that the carburetor is badly worn or there are problems in the fuel injection system. In carburetors with automatic choke, the cause of the problem may be the choke itself, its opening.
It is possible that the ILO CO level is above the maximum specified by the manufacturer. This must be taken into account, but such a fact should not serve as a basis for rejecting the car.
NS emission
When CO emissions are within the established limits, HC emissions should not exceed 1200 ppm. If the vehicle fails this test with the engine idling, it may be tested a second time at approximately 2000 rpm. If the HC level in this case is 1200 ppm or less, the engine is considered to have passed the test.
Exceeding HC emissions can be caused by oil combustion, but this is most likely due to incompletely combusted fuel.
The following reasons are possible:
- a) Spark plugs are in a smelly state or the gap is not properly maintained.
- b) Ignition misadjusted.
- c) Valve clearances incorrectly set.
- d) Low compression in the engine cylinders.
Please note that excessive HC content in the exhaust gases can cause premature failure of the catalytic converter (if installed).
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