Before Tier 4 emissions requirements, non-road diesel engines utilized a mechanical injection system. These systems were not as sensitive to contamination. Because of this, many operators are under the misconception that HPCR fuel systems are also not overly sensitive. In reality, this could not be further from the truth. Dirty or incorrect fuel, water in the fuel and air in the system can all cause damage to newer diesel engines.
Read more: https://www.forconstructionpros.com/equipment/fleet-maintenance/diesel-engines/article/21067733/sensitivities-of-diesel-engine-highpressure-common-rail-fuel-injection-systems