Citroen XM Forum

I have eventually found the source of the poor running that was ....... a duff crank sensor!! Although I had tried other used sensors with no apparent change I also bought a new one a few weeks ago that I thought might be worth a try. There is still a bit of weird behaviour from the tacho, but then it eventually seems to settle down and a few more miles might help.

The car now goes like a rocket, as it should, and what a relief as I was getting close to throwing in the towel!! I feel a bit of a ninny for not replacing the sensor earlier as it does seem logical that it might have taken a battering and failed after the starter ring cracked and came loose. Oddly, however, there was no sign of damage to the tip of the sensor.

Anyway I would just like to say a big thanks to everyone for the interest, advice and support throughout the saga, and in particular Dean, Chris, Mike, Steve, Will and John! Hopefully the BiLlY the 'Essex car', should be at the X in a couple of weeks with the 'Gold one'.

With regards,

Matthew T.

Brilliant! Glad to hear it. I've been keeping abreast of your progress quite often on this thread. Well done Matthew

Many thanks James and it is good that you are keeping up with the Forum, despite not now owning an XM. I am sure the C6 is being enjoyed and you will no doubt also be frequenting other Forum! With regards, Matthew T.

Excellent news Matthew, I too have been keeping a close eye on the topic.

Thank you Ray and that is very kind. With regards, Matthew T.

Well done Matthew, i bet it is a relief to put that one to bed!
Should see a good few years trouble free service now and i will keep my fingers crossed.

D

I thought you swapped on off a working car. I would bee keen to check the wiring connections between the CKP and the ECU. I have known a Xantia diesel lose Tacho due to the CKP conenctor.

That's great news Matthew - that was certainly a puzzle to deal with.

Many thanks chaps and hopefully now I can just enjoy driving the car for a while! The other crank sensors I tried were from a spare engine and my parts box Will, so not definitely known to be good. I also replaced the harness connector plug for the sensor that looked a bit dodgy! Regards, Matthew T.

Really glad you've nailed it, Matt.

Did for some time think it was a timing/crank sensor issue, because of the accompanying tacho misbehaviour. As the engine speed increases, so does the rate at which the sensor has to produce intelligible signals, and if the signals/pulses/waveform is not top-notch, the ECU, tacho and ignition system will have difficulty in operating properly.

Crank sensors, like ABS sensors, are magnetic devices, and can be damaged by rough handling and impacts, which can partially demagnetise them. The waveform they produce then becomes reduced in clarity, especially at higher frequencies. The separation distance of tip to "passing metal" is also a factor. Decreasing the distance will enhance the quality of the signals; limiting factor is risk of the sensor tip actually hitting the moving metal. Not a lot of adjustment available on these sensors. If tacho still a bit marginal, I'd be looking at the separation gap - but no idea how to easily improve it.

That's my explanation, anyway. A great bit of news, all the same!