The key thing to understanding this is to think what each sensor does.
Cam Sensor, this gives the ECU information on which cylinder is firing next, it needs this to support sequential fuel injection and to know which coil to trigger on coil per plug setups (i.e. 2.2, 2.6, 3.2). This information can not be obtained from the crank sensor as its a 4 stroke engine. Some may remember the early fuel injection systems which didnt utilise sequential injection and didn't have a cam sensor.
Most ECU setups can overcome failure of this by firing two spark plugs (true of a DIS pack anyway) and two injectors (or even all four injectors) simultaneously and limit the revs to 4K rpm as part of a limp home mode of operation. Its not the most efficient way of running though.
Crank Position Sensor (or crank angle sensor) - this gives the ECU information on the crank position, this is key to getting the timing of the injection pulse and spark ignition correct (these are referenced to the crank and hence piston position), without crank position the ECU would only now which cylinder was firing next as the cam sensor cannot give accurate positional info to back it up.
As a result no crank signal results in no engine running and thanks to the critical nature of the signal the ECU wont operate spark, injection or fuel pump with it missing.
As a further point to consider on the crank signal, a few lost pulses can be accommodated as the ECU can actually guess pretty accurately where the next one should be, this it can cope with for quite a few pulses.....hence a failing crank sensor often can get you home.
An the subject of this, it is very rarely the cam sensor that fails, as a rule its the cable that connects to it that breaks down so if your stuck and good with a soldering iron, you could splice a new length of cable to it. This is also born out by the fact that the V6 cam sensor pretty much never causes problems (never ever seen one needing changing) but, the cable is routed in a much nicer and cooler environment.
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Topic: Cam/Crank Sensor (Read 2402 times)