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    Posted by Dave Hill on November 14, 2009, 7:15 pm, in reply to "Re: Renault Clio 1.5 DCI Hard Start When Hot"

    Sorry for the delay in posting the fix.

    Ok finally I got a donor car to draw some comparison from. Funny how there are never any about when you need one, & then you are swarmed with them afterwards.

    This animation shows the difference between my "troubled" car & a known good one (at least we think it's trouble free???).



    The result is quite clear & with known good leak off rates, it does confirm that the pump is under performing. This is my first Common Rail pump diagnosis, so I wanted to be sure.


    There is lots of diagnostic info to be gained, by looking at the pressure decay rate, that can be seen in the waveform, after cranking has ceased. In the following animation, the decay rate appears to be greater (i.e. worse) in the example with the good pressure development. Could this be a clue as to a potential problem?



    By studying the time taken for the pressure to drop between 1.5 & 1.0 volts, we can effectively see the rate at which the diesel pressure reduces or decays. As this is one of the most vital aspects of pressure development, it is not something to be ignored.

    Anyhow, after fitting a reconditioned pump we got the following capture.....



    The peak voltage is in excess of 4.0 volts & it makes you question the system performance of the donor vehicle which produced only 3.0 volts (cranking speeds were very similar too). Going back to the earlier capture, where I drew attention to the suspect decay rate on the test vehicle. I believe that this could indicate a potential area of concern. Unfortunately I did not perform any leak off tests on the donor car as I only had it for a short time.

    The car has been with the customer for a few weeks now, without a hint of trouble.

    Regards

    Dave

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