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    Re: Camshaft sensor Questions Archived Message

    Posted by Michael Whitworth on October 5, 2008, 8:39 pm, in reply to "Camshaft sensor Questions"

    Hi Colin,

    As far as I know, there are three reasons for a cam sensor:

    1) Sequential fuel injection
    2) Direct ignition ie coil on plug
    3) Variable Valve timing.

    A 4th would be in the case of common rail, but I guess No1 covers that.

    Once the ecu Knows no.1 position (as opposed to 1 & 4 which is best a cranksensor can give) it no longer needs the cam sensor, that is why on some engines after start the cam sensor can be disconected giving no ill eefect,

    The crank sensor is used usually for both speed and position and once ecu has determined (during cranking) which of the 2 revolutions is firing on no1 it will then use crank sensor for all its firing events.

    The only reason I am aware of that the ECU checks phase against cam/crank is for diagnostic purposes, having said that it all depends on both the operating stategy and the diagnostic strategy designed into the ECU. That is why some cars will flag a cam or crank plausiblility and still run perfect, others will flag a plausibilty and misfire or run poorly. Others will flag no faults but will not run and some will run poorly due to misaligned cam timing and still not flag a fault for it.

    HTH

    Mike

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