as roy said - first test the glow plugs, if you dont have them working the engine will not fire.

this relief valve is a very discussed topic, some people have installed devices in the return line to compensate for the lost pressure. The old 61x pumps had a mechanical adjustable bolt that also held pressure but those engines had hand primer pumps too. This one does not.

It relies on the lift pump on the side of the IP to fill up and bleed the rack area of the pump via the little hole on the relief valve. That little sucker (lift pump) is very powerful - it can collapse your fuel tank given the right chance.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)