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    Re: jag x type 2.0td Archived Message

    Posted by James d on March 22, 2007, 10:46 pm, in reply to "Re: jag x type 2.0td"

    Hi Guys

    Not wishing to teach granny to suck eggs etc.

    My understanding is that the injector coding is, as Alan said, merely an adaptation. The injectors are all flow rated at point of manufacture. The manufacturing tolerances are so close that the factory aren't able to make them all the same, so they rate each injectors flow and categorise them. The coding tells the ecu the individual injectors basal flow rate.

    The coding is a calibration notification to the ECU so that it can alter or adapt its fuel map to ensure that the correct fuel quantity is introduced into the engine. Obviously, this is critical on a diesel as adjusting the fuel quantity is the ONLY way to control engine speed.

    Typically, the ECU can also adjust the fuel quantity (independent of injector coding) in a strategy called SRC. The SRC strategy uses dynamic analysis of the harmonics of the crankshaft rotation (based an algorithm which runs on the CPK output) during engine speeds lower than 1800/2000 rpm.

    Therefore, the ECU can adjust the fuel quantity using SRC, rather than via the adaptation/coding.

    Problems occur when the injector flow rate is outside the range of capability of the SRC. In these cases we may see the lumpy running/misfire associated with injector coding.

    The problem problems prevail if the injectors aren't coded and the 'slack' which SRC has available to keep the engine running smoothly is used up. When other minor issues occur, which the SRC was designed to cope with, a running concern is reported. This is demonstrable via the scan tools serial data.

    Just for info, this is amongst the many subjects covered during our excellent common rail diesel course.

    Kind regards


    James.

    Link: http://www.techtopics.co.uk/Diagnostic%20Training/common%20rail%20diesel%20training.htm

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