Disco 2 Cranks but wont fire

Hi, My td5 engine cranks over but wont fire up, not even trying. Suspected the crank sensor but the engine ecu shows a rpm when cranking so I assume its OK. Rev counter is dead but I picked up on the following in the Rave.
The tachometer, which is located to the left of the speedometer in the instrument pack, displays
engine speed between 228 – 6,000 rev/min. Below 228 it receives diagnostic pulses only.
If I don't turn the ignition off and keep trying cranking it will not start. However 1 cycle of the ignition switch on/off and it starts straight away. It seems as though something is been reset. I don't think its fuel because cycling the ignition switch wouldn't suddenly provide fuel pressure. The Pump primes up every time. What is been reset ? Thanks

Hi, Have you tried starting it straight after a bleed cycle (Ign on and pump accelerator pedal 5 times)? Just trying to rule out air in fuel system.
Our resident electical guru will be along soon
Griff

Hi, No not yet, I am working on the theory that if it starts immediately by simply turning the key on and off. if there was air in the system turning the ignition off and on wouldn't clear any air as it only takes a second to cycle the key and it starts immediately on the second try. the only thing is the pump has run a little longer whilst doing this. I wonder if this extra time allows the pump to pressurise the rail more.

ES4 said:

Hi, No not yet, I am working on the theory that if it starts immediately by simply turning the key on and off. if there was air in the system turning the ignition off and on wouldn't clear any air as it only takes a second to cycle the key and it starts immediately on the second try. the only thing is the pump has run a little longer whilst doing this. I wonder if this extra time allows the pump to pressurise the rail more.

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Surely you could test this latter theory by simply turning the key to "ignition" then just leave it, count to ten or whatever, then see if it starts?

Hi, Yes we have done that a few times, waited till the pump timed out and up to now its started first time, but it will say 50% of the time start straight away, which doesn't help with the diagnostic plan.