BMW X3: N47/B47 Diesel Injector Copper Seal Blow-By ('Black Death')

The direct-injection diesel injectors on N47 and B47 engines are seated against a copper sealing washer that prevents combustion gases from escaping around the injector body. With age and heat cycling the washer compresses and hardens, losing its seal, allowing hot combustion gases to escape around the injector and carbonise externally as a black tar-like deposit. In advanced cases the combustion gases erode the aluminium seat in the cylinder head, requiring machining or head replacement.

• Visible black tar-like carbon crust surrounding one or more injector bodies on top of the engine
• Diesel fuel or exhaust smell detectable inside the cabin with the ventilation drawing outside air
• Rough idle or specific cylinder misfire codes stored in the engine management system
• Hard starting when cold as combustion pressure leaks around the unsealed injector
• Gradual drop in power output as combustion efficiency falls in affected cylinders

1. 1

   Inspect the top of the engine around each injector for black, tar-like carbon deposits radiating outward from the injector body — this is the definitive visual indicator.

2. 2

   Ask a workshop to check injector seat condition and fuel return line sealing before purchase.

3. 3

   On a test drive note any rough idle, misfires, or diesel smell inside the cabin.

4. 4

   Request scan tool data for injector fuel trim corrections, as cylinders with leaking seals often show high correction values.

Parts involved: Fuel injector.

$800 to $4,500 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Have the injector copper sealing washers ever been replaced, and is there a workshop record of this service?”
• “Has the engine ever shown a rough idle, misfires, or had specific cylinder fault codes logged?”
• “Is there any visible black carbonised residue around the injector bodies on top of the engine that I can inspect before purchase?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.