2007 Ford Fiesta 1.2L Petrol · YN07 WKS

The copper base washers on the Delphi common-rail injectors degrade under heat and cylinder combustion pressure, allowing high-pressure exhaust gases and unburnt diesel to blow past. This creates a hard, black carbon residue known as 'black death' around the injector wells in the cylinder head, accompanied by a rhythmic chuffing noise and pungent diesel exhaust fumes in the cabin. If neglected, the carbon glues the injectors solidly into the head, requiring specialist hydraulic extraction pullers or cylinder head removal.

The electronic drive-by-wire accelerator system triggers an 'EAC Fail' warning message on the instrument cluster LCD, immediately sending the engine into limp-home mode with revs restricted to around 2,000 rpm. The primary cause is terminal fretting or moisture corrosion on the pins of the multi-pin connector at the throttle body or intermediate engine wiring harness, though worn internal throttle potentiometer tracks or accelerator pedal position sensors can also trigger the fault code (P0121/P0221).

The front coil springs on the Mk6 Fiesta are notorious for snapping prematurely, often across the lowest coil winding. Road grit, moisture, and road salt collect in the lower spring cup, corroding the protective coating until the spring fractures under pothole or speed cushion impacts. A snapped spring can drop onto the front tyre, gouging the inner sidewall or causing an immediate blowout, making it a critical safety concern and an immediate MOT failure.