The ignition cables are responsible for conducting the required voltage generated by the ignition coil to the spark plug with as little loss as possible.
Due to their installation position, ignition cables are exposed to high loads. At first glance, ignition cables and sets of ignition cables do not show their complex inner workings. In the engine compartment, they have to perform at the highest technical level: Catalytic converters and increasingly powerful, compact engines generate temperatures of up to 200 degrees Celsius, while electronic ignition systems produce high voltages of up to 40 degrees Celsius.000 volts. With increasing age, the brass and stainless steel contacts oxidize. The electrical resistance of the cable increases – and with it the risk of failure of the ignition coils.
Today, PVC Hypalon ignition cables no longer meet these requirements. In current vehicles, even class F silicone ignition leads with a temperature resistance of up to 220°C and a dielectric strength of 40.000 volts are installed. This
- protect against energy loss
- offer optimum protection against vibration, water, acid, oil, gasoline
- meet the highest requirements in terms of interference suppression and electromagnetic compatibility (EMC) with the appropriate connectors.
When installing new cables, care must be taken to ensure that they are not kinked or compressed. Above all, they should not be in contact with hot parts due to the risk of fire.
Plasticizers escape from the plastic sheathing over time. As a result, the sheathing becomes brittle over time. This process can be accelerated by high temperatures and contact with oil or fuel vapors, or even dissolve the plastic completely. Damage to insulation causes ignition voltage to leak to ground. The consequences: Misfiring and rough engine running, with unburned fuel getting into the catalytic converter.
Valuable gasoline is injected at each misfire, but is not burned off. As a result, the environmental impact increases significantly simply due to the additional consumption per kilometer. In addition, the unburned fuel in the catalytic converter can ignite explosively and damage it, so that the catalytic converter can no longer render the dangerous pollutants carbon monoxide, nitrogen oxides and hydrocarbons harmless and has to be replaced.
Since ignition cables are subject to high stresses, the cables should be checked regularly and replaced at the first signs of aging. Defects in the ignition system and catalytic converter usually only come to light through the legally required emissions test. Regular inspection is therefore an important preventive measure that can save costs. Because damage detected in time is cheaper to repair: Replacing complete ignition cables with plugs is much less expensive than catalytic converters affected by consequential damage.
Damage detection for ignition cables
hIn the event of damage, the external appearance of an ignition cable can provide information about the cause of a defect. A precise visual inspection of the ignition cable is therefore the first step in the diagnosis of damage cases. For example, a deformed plastic sheath indicates that the ignition cable has most likely been improperly routed in the engine compartment.
Damage to the ignition lead, however, is not always obvious. Externally intact ignition cables can be checked with a so-called multimeter. This important diagnostic tool allows the resistance of the ignition cable to be read and compared with the permissible resistances.
Replacement of the ignition leads
uIngnition cables in the engine compartment are wearing parts that usually reach their service life limit shortly after one another. Workshop professionals therefore know: If a vehicle is of the appropriate age or has a high mileage, it is advisable to replace the entire ignition lead set right away. In addition, the components of an ignition system are complex and must therefore be precisely matched to one another. Therefore, if an ignition cable is inadvertently retrofitted with a different technology – for example, a carbon ignition cable instead of a copper one – this can lead to massive interference in the engine management system, impairing EMC and even safety-relevant electronic components.
coThis happens – depending on the design of the vehicle – using:
- of a mechanical ignition distributor and distributor cap,
- of a fully electronic ignition module,
- of a fully electronic semi direct ignition resp. Double spark ignition coil.
Since the ignition voltage (U) varies in the high-voltage range by up to 36.000 volts, the ignition cables must be correspondingly protected against breakdown. The ignition voltage must never penetrate the sheathing and flow to the vehicle ground, as this would lead to misfires.
Resistors are used in all ignition lead systems, although a low-loss transmission is basically aimed for. A look at electrical engineering makes it clear that there is no contradiction here. All electrically operated devices generate electromagnetic fields of greater or lesser strength. Although these are harmless in most cases, they may be undesirable under certain circumstances. This is the case, for example, if radio reception is disturbed. The ignition system requires optimum proximity interference suppression to ensure trouble-free operation of radios, communications electronics, engine or transmission control units. The assumption that resistors reduce ignition energy and thus engine performance proves to be a mistake.
The resistors used are dimensioned so that they can be neglected. The ignition lead systems offered by brand manufacturers provide the best interference suppression with optimum ignition performance. The unit for measuring the resistance (R) is Ohm. For ignition leads, this value is in the range of a few thousand ohms or kiloohms. The purpose of this resistor is to reduce the disturbing electromagnetic radiation. This is achieved by limiting the current (I) through the ignition cable and at the same time ensuring that the spark plug continues to receive the required voltage (U). The mathematical formula for this is U = R * I.
Electromagnetic compatibility of ignition cables
In simplified terms, proximity suppression can be thought of as follows: The ignition system consists of a coil and capacitors, electro-technically also “oscillating circuit” called. Suppression resistors (usually 1-5 kOhm) are integrated in the ignition circuit. These reduce electromagnetic oscillations and ensure the interference-free interaction of the various devices. This is called “electromagnetic compatibility” (EMV) designated.
Ignition cables with inductive reactance have a special feature: In this design, the resistance changes depending on the ignition frequency (engine speed). Here, due to the wire coil, greater (inductive) resistance builds up at higher speeds.