BMW X5 Owners & Service Manuals

BMW X5: Fuel System - E32 With M60

Engine Diagnosis
Fig. 16: Identifying Fuel System - E32 With M60 Components

If any of these items are leaking and fail to hold pressure in the fuel rail, the vehicle will be difficult to start.

The cranking time will be excessive and possibly not start at all. For example, If the fuel injectors are leaking, the vehicle will exhibit black smoke on startup.

Diagnosis of these concerns requires a fuel pressure gauge. The residual pressure is monitored on the fuel pressure gauge when the engine is shutoff. Diagnosis is determined by watching the drop in fuel pressure over time. The fuel pressure should not drop more than.5 bar in 30 minutes. If the pressure drops more than.5 bar, the concern should be investigated.

Fuel System - E39/E46 with M54

Engine Diagnosis
Fig. 17: Identifying Fuel System - E39/E46 With M54 System Diagram

Depending on the type of fuel system used, diagnosis will vary. On older fuel systems, diagnosis is simplified due to the ability to clamp off certain components to determine, the origin of the leakdown.

Fuel System - E60

Engine Diagnosis
Fig. 18: Identifying Fuel System - E60 Components

Newer fuel system use a non-return type fuel system with some components mounted externally. Most recently, many of the new vehicle have most of the fuel system components mounted in the fuel tank. This includes the fuel pump, fuel filter and fuel pressure regulator. The only fuel system component outside the fuel tank is the fuel feed line, fuel rail and fuel injectors.

This makes the diagnosis of residual pressure concerns more difficult. Diagnosis of this type of system sometimes requires process of elimination.

If one or more of the fuel injectors is suspected as the cause of the loss in residual fuel pressure. They can be tested using a special tool to "bubble test" the injectors.

Engine Diagnosis
Fig. 19: Testing Bubbles In Injectors Using Special Tool

First the injectors are connected to the test fuel rail supplied with the tool. Then, the fuel injectors are subjected to compressed air. The injectors are then triggered by the test harness to "blow out" any residual fuel.

The test harness is disconnected and the tips of the injectors are immersed in water. The injector tips are observed for any bubbles over time. Any excessive bubbles indicate a defective injector.

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