More like because they are ****e The ecu doesn't Immobilize as such....its always Immobilized...when you try to start the engine it asks the BCM if its allowed to fire the injectors ...if the BCM is immobilized it says no but it also will not crank the engine. If there is no answer from the bcm...

new or used parts? I got a head from some MG rover car from the local scrapper.....they removed it...£80 Cheaper than even bothering about smashed valves :)

You will know by the light on the dash if its immobilised or not. If it is there's no point in crawling about the starter. :)

A leak somewhere letting air in to the fuel line Air in the fuel will cause the pump to make horrendous noises :)

Id replace the rf sensor in the roof, refit the original bcm.....unlock it with the fob.

Yip Ive read all that old hat delphi stuff and much other stuff and been on many courses and have many certificates on diesel diagnostics and made a living from it for years and im sure your dead right..... in theory :) in practice...it'll work just fine :)

The oil can also escape along the splines....

Yes My mate has on in his 90....its converted to td5 using all disco parts, everything except the throttle pedal ....so its a disco as far as the pcm knows. The original disco pcm was sent away to get remapped and immo removed....more for immo remove as the 90 wouldn't go without a bcm to talk...

As to will it work unlocked......yes :) The immobiliser is removed....you can plug it in to anything....disco defender and it will go. As has been said the injector codes will not be correct.....will you notice...NO :) Will it run fine....YES

If you cant slacken them just wait until you go to tighten them back up :)

Heres a plan for you.... wire the sensor to the other side....as in leave the sensor where it is but wire it to the other side with lengths of wire.... Then recheck and see if the fault moves to the other side then you'll know for sure :) You can buy sensors but more or less have to remove...

Have you driven it? Sometimes the faults are cleared but the lights stay on until you drive it.

Cant really help you with your problem... Ive worked in garages for 35years and theres not a lot I cant fix. Theres guys that worked in the Ford main dealer with me and theres no way Id let them even drive something of mine :) Thankfully I no longer work in the motor trade :) I do know a...

The easy way is....cut it in half....slide the bits in...weld back together....job done with next to nothing removed :)

if its there it must work.

could be the fuel pump...can you check the pressure? MAF, and ambient air temp sensor make no difference to starting....all you need to start is crank signal.

A relay is switch that is switched by something. The ign switch could switch on/off hundreds of relays. The power to work all the additional stuff could come straight from the battery.

Bigger tyres - lower gearing = same :)

285/75/16 insa special tracks....about 33" measured from the ground up. It also has 3.9 patrol diffs so that lowered it a bit more :)

I have a 1.6 in my RRC thats fitted with a 300tdi/auto from a Disco 1 and 285 tyres. Fitted it as it struggled....due to traffic....to get fast enough for top gear lock up. So yes it revs more than before but its better than running around changing back and fourth between 3rd 4th, now it locks...