Repair Info - Emissions Repair Explained
Possible Causes of High Diesel Opacity Emissions
In order to pinpoint the cause of excessive diesel opacity (smoke), the following systems (if applicable) and possible defects will need to be checked, usually in this order:
Restricted Airflow
Any restriction to the flow of air into the engine can cause excessive smoke emissions. This includes the air filter, air inlet pipes or ducts, and the intake manifold. Similar to the air filter and inlet ducts, the turbo pressure also can affect the smoke emissions of a diesel engine. The technician will need to ensure that the turbo is running at the correct speed and pressure. A restricted exhaust system may also cause a reduction in the airflow into an engine under certain circumstances.
Injection Timing
The technician must make sure that the injection pump is timed to the correct cylinder and that timing is set to manufacturer's specifications.
Injection Quality
Diesel fuel injectors that are restricted can cause excessive smoke. Other injector defects such as worn valve seat, sticking nozzle, and incorrect opening pressure may also cause excessive smoke. To test or clean diesel injectors, they will need to be removed and bench tested according to the manufacturer's recommended procedures and specifications.
Exhaust Gas Recirculation Devices
Exhaust Gas Recirculation (EGR) devices are used to control NOx emissions in many diesel vehicles but if the rate of EGR flow is excessive, smoke emissions can increase significantly.
Oxidation Catalyst
The performance of the catalyst can have a significant effect on smoke emissions. The technician should refer to the manufacturer's recommended procedures and specifications for testing of these components.
Compression
Engine compression is a measure of piston/cylinder sealing integrity and should be checked with a compression test as per manufacturer's recommended procedure. Compression pressures for each cylinder should be within 10% of each other.
Injection Pump Calibration
If all else fails, the injection pump may require an overhaul or re-calibration.
