The immobiliser lets the car start and run for a few seconds.

If you have a mismatched ecu/bcu/fob going on that is your problem

the current ecu isnt mismatched and was running recently, i only have mismatched ones to replace the set with which wont solve anything. Going to try cam sensors and knock sensors see if that solves it. Got oem crank shaft sensor and it didnt solve it

nice well looks like its not that then

Do you have a OBD2 scanner?
If not consider a www.pscan.eu and then you can match one of your other ECU's to the BCU and at least eliminate that.
It will also give you much more info about the status of the various sensors around the car.

Not seen that, have you used it?

I help Phil develop it by providing some of the ECUs he used for setting it up and helping fund the cloud funding.

I have used mine on several cars, it gives so much more info then my scangauge2. For a start it also accesses pre OBD2 MGR ECUs.

It gives live read outs for all the sensors the ECU uses, not just the OBD2 required ones.

It's also incredibly easy to tune in fobs in Lucas 5AS, he hasn't added Pectron yet as he has only recently got hold of the correct alarm ECU but it's coming.

use it for live data and fob coding!?! I'm sold!

It's alive!!!!!!!!! Well finally after changing literally every thing I could and checking everything I could and 3 garages later finally found the fault to be a slightly corroded wire to the cam sensor, weird because it had continuity when tested with a meter but moving it around and it cracked, new whole wire later and now it runs fine. Biggest ball ache I've every had, nice to know 3 other mechanics were stuck on it as well. Anyway thanks for the advice, it's got a new exhaust and remapped ecu now and sounds the nuts, I'll post up some pics as well as its had a repaint and strip down inside and new dash mods as well

great news :)