Hi I am looking at this vehicle for another garage, the problem is intermittent non-start. If run up to full operating temperature and switched off, vehicle will re-start, but if left for anything between 15 mins and 2 hours it will crank over for anything up to 30 seconds before starting and then running perfectly. If however it is switched off and left for more than a couple of hours it start immediately.

No fault codes are stored. I found 2 cracks in the fuel pipe so replaced those. It has a new filter, new injector seals, new t-piece on top of filter, a good used tandem pump has been tried. A one-way valve has been fitted near to tandem pump and this improves things but not a permanent fix. I have taken a pressure reading at tandem pump, does anyone have the specs for this and also low pressure too? The waveform for in-tank pump looks ok, plenty of fuel at filter when fault occurs. I am suspecting a crack in cyl head but there is no evidence of any mixing between oil, coolant and fuel. Still have ecu comms when fault occurs so main relay is ok.

Vehicle is now usable with the one-way valve but would rather do a correct repair, any ideas would be appreciated.

Frank Massey tests the pressures on one of these here, in the pump duse vibration chapter - if you have a spare 25 minutes.
The Tandem Pump was completely shot, no pressure from it at all, but the engine still started & idled satisfactorily.

http://content.yudu.com/A1dxye/AI-2/resources/index.htm?referrerUrl=

If the in tank pump fails, the Tandem pump cannot generate a supply of fuel to the injectors - the engine cranks / won't start as a result.

The vac operated engine shut off flap in the EGR housing is prone to gumming with a large build up of sludge - these can stick shut, causing a none start.

Starter speed should be 300RPM > on a hot engine.

Coolant Temp Sender reading correctly - these run ropey when the CTS is off the scale.

Jon.