Citroen XM Forum

Thank you for that Chris and I especially appreciated your encouragement and advice along the way! I think I must have been unlucky in that the other used sensors I tried were somehow defective and threw me off the scent. The crankshaft sensor is clearly quite a critical component in the system as you state and my original certainly did get some rough treatment through the failure of the starter ring.

Interestingly I am still getting some mis-behaviour with the tacho, which does then settle down after a time, while re-plugging the ecu also appears to help. I also meant to mention that the engine seems to be running better than ever, which hopefully may be down to all my earlier efforts, to clean wiring connectors, replace the fuel filter etc.!

With regards,

Matthew T.

Great news Matthew, I really hope you get some enjoyable miles now to reward all your efforts!

Many thanks Andy that is kind and it would be good to see you at the X and/or Northern rallies coming up soon! With regards, Matthew T.

If anyone has an oscilloscope that could be put on the output from that sensor, it would nail whether it was providing a good signal or not. Tacho is doing its best to spill the beans, I think.

Just a brief update to confirm that the car is running nicely and I have managed a 270 mile trip to Yorkshire via Suffolk! I was still having some odd behaviour from the tacho on each trip out, despite eventually settling down, which I thought I could fix by changing the gauge. Anyway it turns out the problem seems to be with the ecu since after fitting a spare all is now well. I wonder if something is damaged in the ecu after running with the defective sensor as there is no fault code and reconnecting only gives a temporary fix? Regards, Matthew T.

What a terrific photo, Matt - The Car that Wasn't There!
Did a double-take, and again, expecting to see a reflection in the water. Obviously a Vampire !

You won't have damaged the ECU with a suspect sensor; it would have been receiving a weakened signal at most.
Glad the problem has gone away. What a saga.

Thanks Chris and the photo opportunity was at Welton near Market Weighton where I am staying in East Yorks! There does seem to be a permanent and reoccurring fault with the original ecu, unless it just needs to be run for a little longer. Interestingly the spare replacement ecu is a white label and the original yellow and I did not realize there was different versions for man and auto. The engine tickover is a bit slower with the second ecu but otherwise seems fine. With regards, Matthew T.

I covered another 200 miles today on work visits to Yorkshire and now back down to Suffolk with superb performance thankfully from the car. The V6 certainly pulls like a train and it will cruise endlessly and very comfortably at 70 plus on motorways with power still left for overtaking. On the return leg l refitted the old ecu and as before strange erratic behaviour from the rev counter for a couple if miles before settling down and thereafter completely normal. Unfortunately the issue returns each time after standing, so there does seem to be a permanent fault on the ecu, unless it can be wiped. Luckily I have the spare ecu for the long term. Regards, Matthew T.

I doubt it's firmware related, more likely a broken down/burned out component, or dry solder joint.

Worth having the cover open and a good look at the solder joints.

. . . And giving the ECU pins and connector a good dosing with contact cleaner (not WD40).