It’s common to find inaccurate information circulating in online forums regarding the testing and potential rebuilding of electronic fuel injectors, particularly those used in Mercedes-Benz OM642, OM646, and OM648 diesel engines. These discussions often overlook a fundamental aspect of modern diesel injection systems. Fuel injection supply and timing are not managed within the injector itself. Instead, the Engine Control Unit (ECU) precisely governs these parameters. The ECU relies on a complex network of sensor inputs and pre-programmed design specifications to determine the exact quantity and timing of fuel delivery to each cylinder.
Assuming an injector’s electronic components are functioning correctly – a diagnosis verifiable with Mercedes-Benz diagnostic tools like DAS Xentry – a highly effective supplementary test exists to evaluate the injector’s fuel quantity and timing accuracy. This is known as the fuel flow test or, more commonly, the leak off test.
This test is specifically designed to be performed using manufacturer-approved diagnostic equipment, and for Mercedes-Benz, this means utilizing DAS Xentry.
The procedure is straightforward, provided you have the necessary tools. Every Mercedes-Benz diesel engine system is engineered to return a certain amount of unused fuel back to the fuel tank. When injectors are operating within their specified parameters, this returned fuel volume should be consistent across all cylinders. The leak off test measures this return flow for each injector, typically by collecting the fuel in small, graduated containers. If the collected amounts are similar across all cylinders over a set duration, the injectors are generally in good working order. However, if one or more injectors exhibit significantly higher or lower return volumes compared to the others, it indicates a potential issue. In such cases, the test suggests that the problematic injector should be replaced and subsequently coded to its specific cylinder within the ECU’s system.
In essence, the Xentry injector leak off test is a simple yet powerful diagnostic tool. However, it necessitates specialized tools and diagnostic equipment, like DAS Xentry, which naturally leads to service charges for professional diagnosis and repair.
While the test itself is conceptually simple, the requirement for professional-grade equipment explains why automotive service providers justifiably charge for this valuable service.
