Keihin Injector KN9 size 82cc (Purple) for LPG / CNG Prins VSI 2.0 / VSI-3

If you DO NOT replace ALL the injectors, there are many possibilities of differences between your new and old (contaminated) injectors, so the engine will still work badly and it may even seem that the new injectors do not work properly. All injectors are controlled with more or less the same injection time. The old injectors will dose more gas than the new injectors, because they are still accurate. Because the average mix is still too rich, the engine management will shorten the injection time, so that the new injectors will deliver even less. This will be particularly noticeable with a low engine load (idle) and much less noticeable with a higher engine load (not a high speed, but with the accelerator pedal well depressed).

Therefore it's important to replace all the injectors at the same time.

In most cases the problem is caused by the fact that the gas injectors are contaminated with paraffin (oils and greases from the LPG). The filter upstream of the injectors must ensure that the injectors do not contaminate quickly. This gas phase filter will eventually become saturated and must be replaced every 20,000 km. If the filter is not replaced, the paraffin will no longer be trapped and end up in the injectors. It is not the case that the injectors leak or do not open anymore. But the opening and closing time are no longer correct. The injectors remain open longer than they should (with dynamic behavior), which means that too much fuel is being dosed. (too rich mixture) The injectors will then deviate, especially with short injection times (low engine load). The engine is going to run messy and there are too large differences between the injectors. Cleaning the injectors often makes no sense, because there is often too much wear in the injector occurred, as a result of which the guide of the plunger (sealing disk) no longer has the right fit. The plunger does not go smoothly and lord, but goes up and down stumbling and wobbling. If the injectors are replaced without replacing the filter, the new injectors will soon become dirty again. (read symptom control, no long-term solution)