D2 no start

I have a customers d2 in at the moment. It has an intermittent no start problem. When this occurs the immobiliser light does not blink on the dash. if you go to it and light aint blinking it will not start. you can go back later light blinking and it fires straight up. I thought bcu so I installed a spare I have with matching ecu and truck fired up. However the same problem returned. Wondering if anyone has had this problem before to save me a lot of head scratching.

Ask in the disco section below

Discovery:
https://www.landyzone.co.uk/forum/land-rover-discovery.8