Fuel and Engines
Ford Expedition
Ford Expedition XLT

What is an 'engine coil'?

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March 02, 2007 6:55PM

Don`t Know How These Answers Are Comming Up Seems The Question Changes After Answer Is Given. The Coil Is A Transformer To Increase The Firing Voltage To The Plugs Via The Plug Wires By Way Of The Distrubitor Cap. The Coil Does Not Store The Voltage, It Only Only Increases It. An Engine Oil is basically a lubricant used for lubrication between different engine components which are moving against each other at high temperature and high speeds. It form a thin film between components and also takes away some of the heat. Engine oils are basically petroleum product and chemically made up of hydrocarbons. Today though even synthetic oils are available. Engine oils become less effective after some time and needs to be periodically change. A coil concentrates electrical energy to be sent out by the distributor as a high voltage spark to the spark plugs. The coil is a simple transformer that steps up battery voltage to the thousands of volts the spark plugs need. The coils has two sides, there is the 12 volt or primary side. This side has a few hundred turns of a large diameter wire and builds up the magnetic field in the coils. The other side is the high voltage or secondary side. This side has thousands of turns of smaller diameter wire. The coil uses "electromagnetic induction" to create the high voltage. When we turn off the voltage on the primary side, the collapsing magnetic field induces a voltage in the secondary side producing the thousands of volts the spark plugs need. In a conventional ignition system, the switching on and off of the primary voltage was done with a set of Breaker Points. The points were set inside the distributor and rode on a cam on the distributor shaft. This cam would have 4, 6 or 8 lobes, depending on how many cylinders the engine had. When the points were closed, current flowed into the primary side of the coil creating the magnetic field. When the cam lobe opens the points, the current is turned off and the magnetic field collapses. In an electronic ignition system, the points were replaced with a control module and the lobes on the cam were replaced with a trigger device. The trigger device uses a magnetic force field to induce a small "trigger" voltage in the control module to turn off the current to the coil. As it passes, the module turns the current back on. It is extremely accurate in when it does this. Another advantage of an electronic ignition system can produce higher voltages, up to twice the voltage a conventional system can produce. In a computer controlled ignition system, the control module and the triggering device are replaced by a Crank Angle Sensor (CAS) and an ignition control unit. In newer cars, it has even replaced the distributor. The CAS has a plate that has 360 one-degree marks, four 90-degree marks and two 180-degree marks. There is an infrared sensor that "sees" these marks and tells the control unit exactly where the crankshaft is and the control unit turns off the current to the coil at the precise instant the spark is needed. Since the control unit can do so many calculations per second and the CAS doesn't have to be in the distributor, manufacturers simply did away with the distributor entirely. Now a separate coil is provided for each spark plug. The control unit signals each coil independently. Since the CAS tells the control unit where the crankshaft is at any given moment; it's easy to do. This has made the system more reliable also. In conventional and electronic systems if the coil went bad, you were stuck. Now with 4, 6 or 8 coils, losing one will affect engine performance, but you can still drive. Speaking of reliability, most engines will continue to run even if the CAS fails. The ignition control unit stores basic timing data and when the signal from the CAS stops, it will go into a "fail safe" mode and use the basic data to continue engine operation. In most cases the fail-safe mode will limit speed and/or engine rpm to protect the engine and, in addition to the Malfunction Indicator Light (MIL) alert the driver that there is a problem