Hi guys... it’s been a while since selling my much loved p38 but I need some serious help. We have a 2015 discovery 4 2015 3.0 Ambulance and today it died on the motorway at around 90ish mph, there was a pop sound and speed decreased until we hit the hard shoulder where she stalled and wouldn’t start.
After some playing at the yard we noted that if you remove the oil cap she will start but as soon as you put the oil cap back on there’s a loud whistling sound and it stalls out again. Are there any pointers or areas I should be looking. Diagnostic threw up old fault codes but most recent are air flow mass related. She does smoke white’ish smoke on cranking from the passenger side of the engine bay but not sure if this was there before. Any advice is greatly appreciated as it really must be put back into frontline service. I will add videos of the fault and smoke. Many thanks guys.... this was the best place that helped me so much in my p38 days.

There could be so many causes.
Intake manifolds can split. The throttle butterfly can stick closed.
It could even have a holed piston, broken timing chain or broken crankshaft.
More thorough investigation is needed.