Why is my defender not starting

i have a 2001 land rover defender TD5 it has issues starting i have it at my local garage and they dont know what it is they have replaced a load of parts and have got it down to...

you turn the key and it does not turn over the engine and does nothing but when you spray quick start spray into the air intakes and then turn the key it fires straight up.

what is the issues please help!

when you turn the key the car turns over but does not start

they have replaced the pump

it only starts when you spray quick spray in the air intakes

it only turns over if quick start is sprayed

The parts they have check and replaced

test service
 Error-free machine-to-engine diagnostics
 Checking and measuring the electrical wiring with the multimeter / voltmeter, correct
 Rotation sensor replacement (PMS)
 Engine unit (ECU) replacement
 Checking all relays
 Fuel pump and fuel filter replacement
 Replacement of fuel pressure valve with pressure test verified with 4.5 bar pressure gauge
 Replacement of injector seals and washers
 Ignition replacement (by breakdown)
 With this, the engine does not start with a key, only with Start spray