Rich Mixture

Engines run slightly rich when cold or under full load to protect components. Fault codes P0172 and P0175 report a rich mixture on bank 1 and bank 2. Negative fuel trims show the engine is removing fuel. Black smoke from a petrol engine, a fuel smell from the exhaust and sooty spark plugs are classic visible signs of a rich mixture.

Too much fuel or too little measured air leaves unburnt fuel in the exhaust.

Rich running wastes fuel, can foul spark plugs and can overheat the catalytic converter. Leaking injectors, high fuel pressure and faulty sensors are common causes.