A low fuel rail pressure reading, often indicated by the diagnostic trouble code (DTC) P0087 in VCDS (Vag-Com Diagnostic System), points to a problem in the fuel system. This issue can manifest as poor engine performance, hard starting, or even a complete engine stall. Using VCDS, along with some basic mechanical tests, can help pinpoint the cause of this problem.
One effective method to diagnose a potential fuel delivery issue using VCDS involves monitoring the fuel flow rate. Locate the corresponding Measuring Value Blocks (MVBs) within VCDS that display fuel flow, typically measured in liters per hour (l/h) or liters per minute (l/min). At idle, note the reading, for example, 0.60 l/h. Then, increase the engine speed to 2500-3000 RPM and hold it steady while observing the fuel flow rate in VCDS. If the fuel pump is functioning correctly, the flow rate should noticeably increase. A stagnant or minimally increasing value suggests a problem with the fuel pump’s ability to deliver fuel under load.
Beyond VCDS, a qualified mechanic can perform further tests. A volumetric fuel flow test can be conducted by disconnecting the low-pressure fuel line and cranking the engine while observing the amount of fuel delivered into a measuring container over a specific time, like 20 seconds. A rapid fill indicates sufficient fuel supply. A fuel pressure gauge can be used to measure low-pressure fuel pressure under load, comparing the readings to the vehicle’s specifications. Measuring the fuel pump’s current draw with an ammeter and comparing it to technical data can also provide valuable insights. These tests help differentiate between a failing fuel pump, a clogged fuel filter, a faulty fuel pressure regulator, or other potential issues within the fuel system.
Sometimes, the issue isn’t the fuel pump itself but a faulty sensor providing incorrect information to the engine control unit. For instance, a malfunctioning fuel pressure sensor, similar in appearance to a Manifold Absolute Pressure (MAP) sensor, can incorrectly signal low pressure even when the fuel supply is adequate.
Utilizing VCDS in conjunction with traditional mechanical diagnostic procedures allows for a comprehensive approach to troubleshooting P0087, ensuring a correct diagnosis and efficient repair. While dealership visits can be costly, a local mechanic equipped with the right tools and knowledge can often resolve this issue effectively.
