Contents: Petrol engines ↡ Models with diesel engine ↡
Petrol engines
Start and warm up the engine to normal operating temperature and check that the engine runs normally (the ignition system is in good condition, the air filter is not clogged, etc.).
Before taking any measurements, raise the engine speed to 2500 rpm and hold it for 20 seconds. Reduce the engine speed to idle speed and observe the smoke coming out of the exhaust pipe. If the idle speed is too high or if thick blue or black smoke comes out of the muffler for more than 5 seconds, the engine is faulty. Blue smoke usually indicates the presence of oil in the fuel mixture (engine wear), while black smoke indicates incomplete combustion (the air filter element is dirty, or the carburetor or fuel system is faulty).
Now you will need an exhaust gas analyzer suitable for measuring carbon monoxide (CO) and hydrocarbonate (HC). If you do not have such a device, contact a service station.
CO content
At the time of writing this guide, the maximum CO level at idle is 3.5% for vehicles built since August 1986 and 4.5% for older vehicles.
Since January 1996, much stricter regulations (around 0.5%) have been in force for cars manufactured after 1992 equipped with a catalytic converter. This CO level is difficult to achieve if there are any faults in the carburetor (in the fuel injection system) or catalytic converter, even if the ignition system is in good condition and high quality gasoline is used.
HC Contents
If the CO content is within the normal range, the HC content should not exceed 1200 pm (millionths of a million). 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 to be in good condition.
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Excessive HC content can be caused by oil entering the combustion chamber, but it is more likely to be caused by incomplete combustion of the fuel.
Models with diesel engine
The only exhaust gas test applicable to diesel engines is the measurement of exhaust smoke density. The test involves accelerating the engine several times to maximum rpm without load.
Note: It is extremely important to ensure that the engine camshaft drive belt is in good condition before commencing testing.
Excessive smoke may be caused by a dirty air filter. If this is not the case, seek professional advice.
Note: The above standards for the content of harmful substances in exhaust gases and their smoke are established in Great Britain. In Russia, these standards are regulated by GOST 17.2.2.03-87 and GOST 21393-75.