I have a very strange job here at the moment. Another garage has had the job in for 2 weeks trying to fix it!

When the ambient temperature drops below 6 degrees Celsius, it will not start. It cranks over healthily but doesn't fire. As soon as the air temperature increase, it'll fire straight up.

Checks carried out so far include -

1. Diagnostics test reports no fault codes.
2. Live data confirms correct air, fuel and coolant temperatures.
3. Fuel pressure under cranking rises quickly to 12000 KPA.
4. Injector leak off test carried out.
5. Glowplugs replaced and tested to check for correct operation. They stay on for approximately 20 seconds when the ignition is first switched. Cycling the ignition to preheat the engine 2 or 3 times makes no difference.
6. Starter motor current draw tested at 280 amps when cranking, battery voltage doesn't drop below 10.5 volts.
7. Crank signal good and live data reports cam and crank signals as synchronised.
8. Fuel filter replaced.

The van has done 110k miles and seems to have been pretty well looked after. We haven't yet carried out a compression test on it but the engine runs and performs as expected and will never fail to start in the air temperature is high enough.

Not sure where to go from here!