BMW E46 diesel injector fault and testing
How can you tell an E46 diesel injector is faulty?
Symptoms are vibration at idle, smoke at start-up, knocking and black smoke when accelerating. A bad injector can look good at idle and only fail under load. A fault code for exceeding the smooth running control points to the injectors when it recurs.
How is diesel injector leak-off measured?
1. Remove the air filter housing, the injector wiring harness mounts and the clips of the leak-off lines. 2. Pinch the leak-off line closed before the injector connections. 3. Attach a transparent hose (inner diameter about 10 mm, length about 40 cm). 4. Start the engine warm and see how much fuel collects. The return line of piezo injectors must have constant back pressure, so they cannot be measured with home methods.
How much can a diesel injector leak off?
The acceptable leak-off is under 20 ml in two minutes. With a new injector the amount is typically about 10 ml. Most leaking injectors are fixed by renewing the seals.
Does a replaced injector need coding?
Yes. A replaced injector that has not been coded can cause knocking. Coding tells the engine control the injector's individual characteristics, and the correction values are worth checking again afterwards. If the injector leaks outward from the high-pressure pipe connection, the fault may be just the connection seal.