Gasoline engines
Start and warm up the engine to normal operating temperature and check that the engine is running normally (the ignition system is in good condition, the air filter element is not clogged, etc.).
Before starting any measurements, raise the engine speed to 2500 rpm and hold it for 20 seconds. Reset the engine speed to idle and observe the smoke coming out of the exhaust pipe. If the idle speed is too high, or if thick smoke comes out of the muffler for more than 5 seconds (blue or black), means the engine is faulty. As a rule, blue smoke indicates the presence of oil in the working mixture (engine wear), and black smoke - for incomplete combustion (the air filter element is dirty, or the carburetor or fuel system is faulty).
You now need an exhaust gas analyzer suitable for measuring carbon monoxide (SO) and hydrocarbons (NS). If you do not have such a device, contact the service station.
Carbon monoxide content (SO) in exhaust gases
At the time of writing this manual, the maximum CO level at idle should not exceed 3.5% for vehicles manufactured since August 1986 and 4.5% for older vehicles.
Since January 1996, much stricter rules have been introduced (about 0.5%) for vehicles manufactured from August 1992 equipped with an exhaust gas catalytic converter. This level of CO content is difficult to ensure in case of malfunctions in the carburetor (fuel injection system) or catalytic converter, even if the ignition system is in good condition and high quality gasoline is used.
Hydrocarbon content (NS) in exhaust gases
Provided that the CO content is within the normal range, the HC content should not exceed 1200 pm (ppm). If the engine does not meet these requirements at idle, the test can be repeated at approximately 2000 rpm; if the HC level is 1200 pm or less, the engine is considered serviceable.
Excessive HC content may be caused by oil entering the combustion chamber, but it is more likely that this is due to incomplete combustion of the fuel.
Diesel Models
The only exhaust test applicable to diesel engines is exhaust smoke density measurement. The test involves accelerating the engine at no load to maximum speed, performed several times.
Note: Before proceeding with the test, it is necessary to make sure that the engine camshaft drive belt is in good condition.
Excessive smoke may be caused by a dirty air filter. Otherwise, seek expert advice.
Note: The above standards for the content of harmful substances in exhaust gases and their smokiness are established in the UK. In Russia, these standards are regulated by GOST 17.2.3.03-87 and GOST 21393-75.
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