Citroen XM Forum

No CKP signal will cut the engine as the ECU doesn't fully energise until the signal is received.

That was my understanding Will, that if there is no CPS signal the ecu does not register a need for either spark or fuel. Fortunately I have a spare sensor which I can try tomorrow. Unless I have just been unlucky with a broken wire or poor connection, my only other idea is something connected to the immobiliser, but then I do get the keypad green light and I think I would have spark and no fuel? With regards, Matthew T.

Certainly on the Fenix 4 you don't get either spark or fuel if the ckp signal isn't received by the ECU. The connector near the throttle body can give trouble.
The immobiliser provides power to the ECU, but the spark and fuel side is further switched anfter a crank signal is received.
From memory, the coil power is only supplied once the crank signal is received, so is a pretty easy check to make.

Well after some further checks this morning the crank sensor itself does not appear to be the issue as I have tried two other new sensors with no change, except for the behaviour of the rev counter that may not be significant. There is definitely no spark or fuel ir life at the pump so something is causing obstruction, either a wiring/ connector issue or some other control. I will try another ecu but I am not too hopeful. With regards, Matthew T.

MTXM wrote: ↑

Fri Feb 15, 2019 6:27 pm

I now have an issue with starting which is odd as I only disturbed a few components for the gearbox work - it may be a unlucky coincidence! It is a bit of a mystery as there seems to be no spark or petrol at the moment! I am wondering whether the crank sensor has failed as I have tried other ignition coils and modules and the fuel pump seems dead! Regards, Matthew T.

Does the fuel pump prime when you turn the ignition on?
Green light on the keypad, no fuel pump or spark then i would double check the two multi plugs over the gearbox are plugged in properly or look at the fuel pump relay and ignition relays in the ECU box.

Immo will cut fuel injectors and ignition, if there was an immo issue you should get red and green lights on.

D

Thanks Dean and there is no priming of the fuel pump although I have a green light on the key pad. I have also fiddled with the two multi pin plugs and ecu box relays with no change. The ecu relay powers up with ignition first position but not the injector relay that I am sure must be significant, it is just finding the cause! With regards, Matthew T.

If there is any fault a code should be logged. Even the Ckp logs a fault as it is compared to the cam sensor, so the engine knows the engine is rotating and is expecting a crank sensor output.

Thanks Will but I do seem to have finally solved the problem, which was a faulty injection relay against the ecus! I tried cleaning the contacts on the relay outside and inside but to no avail and replacement has been necessary. After almost giving up I decided to switch the whole bank of relays with those on the car parked alongside and it then started. There is a lot to be said for having more than one XM. I probably should have latched onto the relay sooner but it had not been touched in the work and just one of those unlucky coincidences I guess! Thanks again Will and Dean for your advice along the way. With regards, Matthew T

Hi Matthew,
Highly amused to see you've taken on yet another V6 .... what are your ultimate plans for the car, surely you don't need seven ? - cheers Richard.

Thanks Richard and it was good to hear from you again! I have actually had this car for around three years but it has been slow progress, plus one or two complications. Hopefully I can now get the necessary welding done on the cills and put it on the road at last! Of course you are right I do not strictly need as many cars (six actually), but as with the other acquisitions there seemed to be very little interest when advertised and it would have otherwise probably been scrapped. With regards, Matthew T.