Diesel Engine (test, diagnostic)
Working on the Diesel engine becomes necessary when:
- it is difficult to start,
- the results of the exhaust gas testing are unsatisfactory,
- the exhaust gas is discoloured,
- the fuel consumption is too
- unusual noises from the engine (especially when it is warm).
Blueish exhaust fumes are always an indicator of oil in the exhaust gas. In this case, a close look at the compression is wise. The first, and in some modern engines only possible test, is the electronic testing of the
current flow to the starter, which must be carried out during the individual compression strokes.
Should a test with dismantled glow-equipment not be possible, then, in the case of the injection pump, the piping between the pump and the nozzle must be removed, with the Common
Rail, the entire fuel-rail
(see picture) must be dismantled. To distinguish between a defect, e.g., between worn out cylinder sleeves or leaky valve-guides, a pressure-loss test should be carried out. If the engine is unwilling to start, the
procedure is similar, however, in the case of the side-combustion chamber system, the glow-system
must first be checked. Loud knocking noises are also a result of something wrong in the glow-system. Should the noises persist, even when the engine is warm, there may be a defect in the regulation system
(delivery begin) or the Cetan value may be wrong e.g., through too much petrol in the fuel.
In particular the older Diesel engines indicate that all is not well by sooting heavily (black exhaust fumes).They are produced by too much fuel or too little air-supply. Therefore, the air-filter should first be checked, then
the injection system. In this case, either the regulation (wrong injection begin) is defective or the injection nozzles have a post injection drip.
The best way to find a defective nozzle in individual injection lines, is to
loosen the nut while the engine is running. If the running of the engine doesn't change, then this cylinder is doing nothing to stabilize the performance, then obviously something is amiss here. Defective nozzles can
also be discovered when checking for oil-leakage. If more fuel flows from one than from the other nozzles, then the nozzle-needle is worn out.
Slight varying during the exhaust gas testing can be compensated by an idling value at the maximum tolerance limit or a full-load RPM at the minimum tolerance limit. When working on the injection system, with the
very high pressures common today, one must pay particular attention to the prescribed torque values when re-assembling. requirements, because of substantial pressure in the system nowadays.
1. In the case of unfavourable exhaust values, the air-filter should always be checked first, only then should the injection system or the engine (e.g., the compression) be examined.
2. The exhaust gases from the
Diesel engine, e.g., during a turpidity test, should be taken up as completely as possible and conducted into the open air by the extractor fan.
3. Of course, the noise pullution level my only exceed the average limit
a few times a day (less than 10 times). 09/11