When reading out the error memory, the control unit reports a higher injection amount for one of the cylinders. This means that the injection times of the individual injectors can be adjusted separately, and that at least one injector has reached the limit value as preset by the software.
Reasons for differing injection times
With this type of high pressure and in spite of tight manufacturing tolerances, it is not possible to guarantee exactly the same injection amount with the same injection time for all the cylinders. Apart from that, coking and other impediments will occur with increasing running time.
Control of the injection time
Via the sensors, e.g. in the flywheel, the control unit registers the rev changes in the power strokes of the individual cylinders. Cylinders with less thrust are assigned a slightly longer injection time. The balancing of the cylinders does not take place by comparing the injection amount, but by the steady pressure resulting from the burning fuel.
The additional injection is limited
If only the effectivity of the burning fuel is being controlled, it's failure to occur may also have other reasons. If e.g., the compression in one cylinder is lower, the control unit would also try to compensate for the weaker performance of this cylinder by increasing the injection time. In the case of small deviations this may even be successful. Should however, the deviation from the average of the other cylinders be considerable, this would lead to an inefficient, massive over-injection. In fact, the negative consequences for the mechanics, the consumption and the exhaust gas values would be considerable. Therefore, over a certain limit, no further injection may take place and an error-point must be registered.
Consequenses of failing to repair
Should the leakiness be found between the high pressure area and the flow-back and if, e.g., through too much play in the injector needle causes faulty controlling, the worst case could be that the engine would no longer start. If the leak is between the high pressure area and the cylinder, engine damage may even result. The somewhat greater amount of liquid fuel can then develop so much heat, that the melting point of metals is exceeded.
Why not simply replace the injector?
It must, first of all, be determined whether the exceeding of the permissable injection amount, is in fact, caused by a faulty injector. If, for example, the problem is caused by a bad filling of the cylinder, or its insufficient compression, the problem will not be solved by replacing the injector.
When changing injectors, saved data to be erased.
A compression-check can simply not be avoided and e.g., by measuring the starter current, any suspicion can easily be confirmed or discarded. In the latter case of course, the matter has to be looked at more closely. Depending on the workload, it is possible to swap two injectors around, just to see if the fault still occurs. If the fault is still there, then the replacement is probably justified.
Due to the variety of systems, the flow-back measuring is not always possible. There is the CR-3-system by Bosch, which requires 10 bar back-pressure in the flow-back. This is difficult to obtain using a reduction piece and a manometer. The workshop equipment shown in the above picture guarantees at least the individual flow-back connections. Whatever you do, don't let differences of approx. 30 percent make you nervous. 07/10