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Engine health check
Fuel Supply System
The performance of a fuel injector is effected by both wear and the quality of build. Most automotive fuel injector nozzles have a manufacturer replacement recommendation in the region of 60,000 miles - many injectors will give satisfactory performance for far longer than this although performance with different fuels can vary.
Due to insufficient quality control some new injector nozzles, from established injection equipment manufacturers, have been found to under perform. For this reason it is recommended to thoroughly test new injectors or injector nozzles before fitting.
When examining injector performance particular care should be taken to ensure that needle seat leak by is well within manufacturers specification. With mechanical injection systems carefully adjusting the injector opening pressures to the same value ensures that fuel injection timing is consistent from one cylinder to the next.
Ensuring that the engine temperature regulation is operating correctly provides confidence that temperatures within the engine reach that necessary for good combustion. On a liquid cooled engine such a check would include checking, and if necessary replacing
- radiator cap.
- pressure testing the cooling system.
- the operation of the cooling fan - check for correct operation of a viscous coupling.
Unburnt fuel can migrate past the piston into the engine lubricating oil. Oil analysis labs will complete thorough testing of the engine oil. Some simple tests can be performed to asses oil contamination.
A drop of oil is placed onto blotting paper or a business card which is supported in a horizontal position, not resting on a surface. After six hours the blotter is examined.
- If soot particles remain largely where the drop was deposited it suggests that the oil is overloaded with soot or contains coolant.
- Soot particles travelling with the oil suggest that the dispersant additives in the oil is still functioning.
- After 24 hours the blotter is once again examined, preferably under UV light. If a visible outer ring is present it suggests fuel dilution. Well defined inner rings suggest at least one cylinder is not running correctly.
A sample of used oil is placed in a fridge for 8 hours. When the sample is tipped it should flow. The sample may be much thicker. If the sample wobbles like jelly it suggests that the oil is polymerising due to fuel contamination. If the sample continues to wobble when it has returned to room temperature fuel contamination is severe.