It’s common to find online forums filled with inaccurate information, especially when it comes to complex automotive systems like electronic fuel injectors in diesel engines such as the OM642, 646, and 648. Many discussions miss a crucial point: fuel injection supply and timing aren’t controlled within the injector itself. Instead, the Engine Control Unit (ECU) governs these parameters, relying on a multitude of sensor inputs to determine the precise fuel delivery quantity and timing.
Assuming the injector’s electronic integrity is verified – ideally through a diagnostic scan using Mercedes-Benz diagnostic equipment like DAS Xentry – a highly effective supplementary test for evaluating fuel quantity and timing is the fuel flow test, also known as the leak-off test.
This test is seamlessly integrated with manufacturer-specific diagnostic tools; in the case of Mercedes-Benz diesel engines, DAS Xentry is the go-to system.
The procedure itself is straightforward, provided you have the necessary tools and diagnostic capabilities. Essentially, every Mercedes-Benz diesel engine recirculates a certain amount of unused fuel back to the tank. When injectors are functioning correctly and within specification, this returned or “leak-off” fuel volume should be consistent across all cylinders. The Xentry Injector Test measures this return flow, capturing it in small, graduated containers for each injector. If the collected amounts are similar across all cylinders over a set test duration, the injectors are generally deemed healthy. However, if one or more injectors exhibit significantly higher or lower return volumes, it indicates a potential issue. In such cases, the test suggests injector replacement, followed by coding the new injector to the corresponding cylinder in the ECU.
In essence, the Xentry injector test is a simple yet powerful diagnostic tool. However, it necessitates specialized equipment and diagnostic software, which is why professional automotive technicians rightly charge for this valuable service.
