Modern cars use a variety of sensors to monitor engine functions and to ensure reliable and efficient operation. The camshaft position sensor is one that imparts vital information to the electronic control module (ECM) or to the ignition module. This allows, among other things, for changes to be made electronically in the spark advance. Because of this, a faulty camshaft position sensor may result in a no-spark situation, especially if the engine is configured to have the camshaft position sensor perform the role traditionally played by a distributor.
The camshaft position sensor sends signals to either the ECM or the ignition module to let the computer that is controlling the ignition coils know the position of each piston (for example, whether it is on the power stroke, the compression stroke, etc.). Such information is essential to the smooth operation of the engine, because if the spark arrives too early or too late, there is either a misfire or nothing at all.
As the camshaft turns, the position sensor registers not only where the camshaft is, but also, by extension, where the valves and the pistons are. In order for an internal combustion engine to run well, there must be spark introduced while the piston is on the compression stroke (i.e., when the piston is traveling upward and while there is fuel and air in the combustion chamber). If the camshaft position sensor is malfunctioning, the computer may not be able to determine the correct time to fire the ignition coils, and there may end up being no spark. Even if the computer is able to use the information coming from another sensor -- the crankshaft position sensor -- to gauge the proper timing, the engine may not run very well because there will no longer be a way to control spark advance, and symptoms such as hesitation or stalling while accelerating may occur.
Electronic Spark Advance
To illustrate the operation of electronic spark advance, consider a car traveling at 55 mph at normal operating temperature, running at moderate rpm, and with the throttle partly open. In such a case, the computer would calculate the need for spark advance (when the spark plug fires sooner in the compression stroke than otherwise) to be almost maximum. But if the camshaft position sensor is not working, the car's computer cannot know when to fire the ignition coils to achieve the desired advance.
Distributorless Ignition System
In a distributlorless ignition system, the function of the distributor is often filled by a camshaft position sensor, which tells the computer when to fire the ignition coils. The advantages to such a system include the absence of a rotor or distributor cap, which may burn or crack with use, along with the absence of a vacuum advance diaphragm, which can rupture or leak. But when a camshaft position sensor takes the place of a distributor, failure of that sensor could result in there being no spark.
Camshaft position sensors use either a toothed wheel attached to the camshaft, which, by use of the Hall effect, introduces a current in the sensor at specified intervals, or they use LEDs, which shine light onto a slotted wheel attached to the camshaft, behind which is the sensor equipped with photoreceptors.
- Modern Automotive Technology, James E. Duffy, 1998
- Photo Credit Image by Flickr.com, courtesy of Reg Mckenna
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