Ignition coils are under more strain than ever. When failure happens, workshops need to know what to look out for and what to replace them with.
According to Delphi, the increased use of hybrid, start-stop, and smaller engines by vehicle manufacturers to comply with strict emissions regulations has significantly increased the demands placed on ignition coils. The coils are required to generate up to 45,000 volts for efficient combustion and are expected to operate in larger temperature swings, with more high-load start cycles, increased performance expectations and weight reductions.
“Ignition coils today deliver the high electrical loads of starting cycles far more frequently due to start-stop and hybrid engines,” Luke Garratt, technical services manager at Delphi, explains. “Short urban journeys can extend gaps and increase starting cycles further. Ignition coils still need to reliably deliver a strong spark, at the right time, to the right cylinder thousands of times per minute.”
Every coil in the Delphi line is manufactured to exacting specifications according to the firm’s global OE experience. Construction uses high quality wiring, insulation and coatings, along with efficient windings. Vacuum production ensures air bubbles are removed from materials to prevent arcing or shorting. All Delphi ignition coils will additionally have been subjected to thousands of hours of testing before being released for sale to ensure they can withstand vibration, temperature swings and moisture over many years of use.
Multispark ignition coils have recently been developed by Delphi and will soon be made available to the aftermarket. They fire multiple sparks rather than a single spark on each cycle to burn fuel more efficiently.
Delphi’s UK and European range occupies a market-leading position, with 89 per cent of the car parc covered – and particular strength on hybrids. There are over 430 coils in range, comprising oil filled, cassette, pencil, coil on plug, distributor coil and distributorless coil types. As part of its commitment to providing complete workshop solutions for independent garages, Delphi’s Masters of Motion hub includes videos on replacing and testing ignition coils.
Failure causes
Ignition coils are designed for durability but can fail due to several factors:
- Damaged spark plugs or wires can cause the coil’s voltage to exceed 35,000 volts, damaging internal insulation and leading to misfires or starting issues.
- A worn or widened spark plug gap also forces the coil to generate higher voltage, risking overload and overheating.
- Vibration from the engine can damage coil windings or loosen connections, further straining the system.
- Overheating from engine temperatures reduces its ability to conduct electricity.
- Varying resistance within the coil can lead to system damage, while excessive moisture, such as from oil leaks or water, can degrade both the coil and spark plug.
Identifying and resolving these root causes is essential to prevent repeated coil failure.
Symptoms of a faulty ignition coil
A faulty ignition coil can cause several engine performance issues, including:
- Check engine light: A malfunctioning coil triggers the light due to poor engine performance.
- Poor fuel economy: Less spark energy leads to inefficient combustion, reducing fuel efficiency.
- Backfiring: Unburnt fuel in the exhaust causes backfiring, potentially damaging the exhaust system.
- Stalling: Irregular current to spark plugs results in stalling or failure to restart.
- Misfires: A weak coil causes engine misfires, especially during acceleration.
- Starting problems: Insufficient spark affects start-up, potentially preventing the vehicle from starting altogether.
Troubleshooting
- To diagnose a faulty ignition coil, start by reading fault codes and comparing live data from the suspected coil with a known good one.
- Inspect the coil for physical damage and check the spark plug and wire resistance.
- Use a multimeter to measure the coil’s voltage supply (above 10.5V) and test primary (0.4-2 ohms) and secondary (5,000-20,000 ohms) circuit resistance, following manufacturer specs.
- A zero reading indicates a shorted coil, while a high reading suggests an open coil. For multi-wire coils, consult the wiring diagram for specific design details.
Replacing the ignition coil
- To replace an ignition coil, turn off the ignition and locate the faulty coil. Unplug the connector, remove the securing bolts, and lift the coil out.
- Apply dielectric grease to the new coil’s foot and socket to prevent corrosion, then install it. Tighten bolts and reconnect the connector. It’s advisable to replace all spark plugs at this time.
- Use a diagnostic tool to clear fault codes and reset the engine management light. Finally, perform a road test.
