1. The main focus of the visual inspection is to verify the registration certificate/chassis number/engine number and number plates issued by the Department of Motor Traffic.
2. During the visual inspection, the maintenance status of the vehicle's exhaust system (silencer) and external parts added and modified are checked.
3. Visual inspection is done to verify whether the vehicle's engine is at idle and can be subjected to immediate maximum acceleration, which is important for the smoke inspection method.
4. The vehicle's fuel tank cap and plug cover (plug top) will be checked here and should be sent for inspection in good condition.
5. The engine is checked for water/lubricant/fuel leakage or damaged parts (broken, burst parts) making unwanted noises. The reason for this inspection is to prevent damage and inconvenience to the vehicle or the employees being inspected during the emission testing of the vehicle. Thus, if a vehicle without a proper condition found to be fault during the emission testing can make both parties inconvenienced. Sometimes malfunctioned governor along with oil leakages can create engine run-over conditions which leads to instant fire.
Therefore, if the visual inspection fails on these points, the vehicle will not be referred for an emission inspection.
A diesel vehicle is failed when K factor (Smoke opacity factor during sudden acceleration) exceeds 4.0 and the difference of lowest and highest K values in between each acceleration exceeds 1.0
A. Things you should be aware of when a diesel vehicle fails
Loss of cleanliness of the exhaust system of a diesel vehicle is a major contributor to failures. While performing the smoke test, the carbon particles deposited in the exhaust system needed to be flushed during flushing cycles (first three quick accelerations). However, carbon particles accumulated in the silencer will not be fully removed during the flushing cycles since this test is done one time per year. Because of this, it is very important to keep the silencer clean unless otherwise it will be the major cause for failure.
When a diesel vehicle fails at smoke test, follow these steps before attending a repair.
1. Make sure that the exhaust system of the vehicle is clean.
2. Check whether the air filter is clean. If it is in a condition that cannot be cleaned and reused, it should be replaced. (Special attention should be paid to use high quality spare parts recommended by the manufacturer).
3. Check and confirm whether the diesel injector and pump are working properly. Here you need to take the help of a mechanic. All diesel injectors should be pressurized and tuned so that they open at the same pressure and inject diesel correctly.
4. Ensure that the diesel injector pump is in proper working condition, otherwise the pump must be repaired and tuned. (Here again you should take the help of an experienced diesel pump repair technician.)
5. If engine oil (lubricating oil) burns excessively, the vehicle engine should be inspected by an expert mechanic and he will determine the repairs that need to be done.
A petrol vehicle fails due to the amount of CO and HC pollutant gases exceeds the standard
| Vehicle Type | Carbon monoxide CO (%v/v) | Hydrocarbons HC (ppm %v/v) | Remarks |
|---|---|---|---|
| Petrol vehicles other than motorcycles and tricycles | 3 | 1000 | Start with idling and 2500 RPM |
| Petrol motorcycles and tricycles | 4 | 6000 | Start with idling and 2500 RPM |
When a petrol vehicle fails, the first thing you need to do is read and understand the failed smoke certificate correctly.
A. Failure due to HC value exceeding standard emission standards.
HC stands for Hydrocarbons. Both fuels and lubricants you use in your vehicle are categorized as hydrocarbons. If the HC value exceeds the standard emission figure, it means that the unburnt fuel particles and partially burnt fuel are passing through the silencer of the vehicle. If unburned fuel fractions and partially burnt fuel fractions (HC) are emitted excessively, it may be caused by the following factors.
1. Ignition system is malfunctioning. (Insufficient spark required for complete combustion of the petrol-air mixture. So need to check the spark plugs, wires etc.)
2. Insufficient supply of air for combustion. (Clogged air filter.)
3. Lubricant particles has been mixed to the combustion due to engine wear. (Unburnt and partially burnt lubricant exits the silencer as HC. This has to be inspected by a mechanic.).
4. In case of a two-stroke engine, since petrol is mixed with lubricating oil (2T) and when it is not mixed in correct quantities, unburned lubricating oil and partially burnt lubricating oil (2T) leave the silencer as HC. The recommended ratio is to mix 30 ml of 2T per 1 liter of petrol for three-wheeler engines (This ratio may vary depending on the condition of the engine.)
B. Failure due to CO value exceeding standard emission standards.
Factors affecting the carbon monoxide CO value to exceed standard emission value
1. The main reason for the increasing in carbon monoxide CO value is that the mixture of gasoline and air which requires for complete combustion is not in the right ratio.
2. The most common factor affecting to the wrong air fuel ratio is the air filter which fails to provide the required amount of air for combustion. If the amount of oxygen required for combustion does not reach the combustion chamber through the air filter, complete combustion will not take place and partially burnt carbon produces CO instead of Carbon dioxide CO2.
3. Carburetor or EFI system not properly tuned is the other main cause of high CO value.
These errors can be corrected by cleaning or replacing the air filter and having the fuel injection system (carburetor or EFI system) cleaned and tuned by an experienced technician.