Inside Line: Cambiare


According to Cambiare, the Fiesta’s ignitions system appears to be a bit of a weak spot. In fact coils and leads account for 7 out of the top 10 selling lines for this model. Misfires, hard starting and poor running could all be the result of these parts failing.

Coil and Lead Systems

While most newer vehicles are fitted with very reliable, low maintenance coil packs, pencil coils and rail coils, there are still plenty of coil and lead systems out there. In fact around 16 million vehicles on UK roads rely on ignition leads. This population is actively growing thanks to the new generation of small vehicles such as the Fiesta (and also the KA, Fiat’s 500, Panda and Punto models, as well as Mercedes’ Smart Car).


Failed or failing coils and coil packs normally can be detected through a number of symptoms, including:

  • Poor idle or poor engine running at low speed
  • Misfire
  • Poor fuel consumption
  • A loss of power
  • Poor starting

Engine diagnostic tools can help identify the source and location of the fault, but these should be used with caution as they can lead you to incorrect diagnoses, while fault codes will often identify where the fault is, they won’t always identify other systems that are affected by the failure and which could even be the cause of the failure.

Common fault codes pointing towards possible ignition coil faults include:

  • P0351 Ignition coil A, primary/secondary – circuit malfunction
  • P030X Misfire detected in cylinder 3 (in this case)
  • P0300 Random/multiple cylinder(s) – misfire detected

Making a comeback

Many people believe that ignition leads are “a thing of the past,” yet the UK aftermarket for ignition leads is currently valued at £10m at trade level, meaning there are plenty of sales opportunities open to the independent aftermarket.

Original equipment manufacturers use three technologies for ignition leads: copper core, wire wound core (reactive), resistive core. The Fiesta, as with the majority of small cars, utilises resistive core technology as this the least expensive type of coil to manufacture.

Ignition leads operate in a hostile environment, where they are subject to attack from extreme heat and chemicals. Oil, coolant and fuel vapour can cause connector contacts to oxidize and corrode and the plasticizers to escape from the plastics used in the casing.

The result is a brittle lead. Damage to the lead insulation causes the ignition voltage to flow to ground, resulting in misfiring, rough engine running and unburned fuel in the catalytic converter. Consequently, fitters should be getting into the habit of regularly inspecting ignition leads and replace them at the first sign of ageing.

Beware of rationalised lead sets

Using OE-quality replacement leads is vital on modern vehicles, yet some suppliers are rationalising their ranges by supplying extra-long leads in a set that seems to fit a wider range of applications.

While a non-OE-quality part will often seem to fit a selection of vehicles, it will not offer an exact fit and this can lead to problems, as the excess cable of these leads cannot be accommodated within the allotted space and may become trapped or damaged, resulting in early failure. Other problems include: inadequate radio suppression affecting radio reception and any number of electronic sensors; and inadequate protection from heat and chemical attack.

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