Not exactly related to this topic, but since fuel system pressure leaks has been mentioned, I wanted to share some knowledge.

On the M103 engine (and others) worn mechanical fuel injectors are also a common cause of system pressure dropping off fast after pump shutoff. Not saying this is the problem in this case, but rather then to also look elsewhere besides the fuel accumulator when there is an issue that prevents the fuel system from remaining pressurized on spec for at least 30 minutes afterwards. Basically worn injectors might start to "weep" fuel into the affected cylinders while the engine is off. To find the bad injectors they would have to be tested individually to determine which ones are leaking. This weeping sometimes manifests itself as hard hot starts, because besides of the pressure drop itself, on a hot engine there might also be pockets of air forming inside the fuel lines if the fuel is unpressurized, which contributes to the hard starting problem. Engine fuel flooding can also happen and make the engine very hard to start because excess fuel inside the cylinder(s).

Under the same condition cold starts would usually still be ok, but sometimes the engine just catches and then shuts off unless you "catch it" with the accelerator. What happens is that a bit of fuel puddles inside the leaking cylinder(s) and the engine first starts off with this fuel, but it's not enough to maintain combustion afterwards, so it stumbles and dies, or if there is excess fuel the engine just "bubbles" a bit after startup and then catches on and idles perfectly afterwards. After it initially dies, it usually is a bit harder to start the engine because it has to be cranked for a few seconds and wont start until fuel pressure has once again build up. Remember the fuel pump only runs for a second when you first turn the ignition key, and then only runs continuously on cranking or with a running engine, so it needs those additional seconds of cranking to be able to build up the pressure before the engine fires up once again.

The remedy of course in this case is to change all 6 injectors and seals, and if that was the problem your engine should once again start right off the bat every time and under any conditions with no more then one or maybe two seconds of cranking required.

Hope this info might be useful to someone. Corrections and/or additions are of course welcomed.

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W163 ML230 EURO SPEC 1999
W124 300E 1986