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[Doctor Gollum]

Have previously had the occasional starting issue with fuel pump not priming. Has happened three times over the last six months. Always started OK with a slap of the tank whilst cranking. Happened again on Sunday, restarted OK, but struggled under load, eventually stalling. Wouldn't restart to better position it on the drive. Conclusion being that the fuel pump finally rolled over. Ripped it all apart, (including draining the couple of gallons in the tank) to liberate the fuel pump with a view to swapping out the actual pump with an used replacement.

Obviously hit an immediate snag

The pump, housing and plumbing are completely different. Current one is a VDO unit and replacement is Pierburg, (sold as spares unit due to a busted external spigot).

Tested original pump off the car and it spins up just fine, reconnected it electrically as it should be and tried ten times. It dry primed every time. Doesn't mean the fuel pump isn't weak to the point of cutting out.

So, to the conundrum...

Do I:

1. Throw it all back together and hope it works properly.
2. Obtain a replacement fuel pump assembly with the delay that entails.
3. Take the £150 and run.

[Viral_Jim]

4. Pick up a generic electric in-line pump and wire it to a switched live?

[Doctor Gollum]

4. Pick up a generic electric in-line pump and wire it to a switched live?

Which would involve pulling the fuel through the original pump... I should add that the current pump is an in tank one and is integral to the sender unit.

[dave the builder]

no way of getting just the pump(replacement) to fit into your old housing 
I've had fuel pumps spin up fine on the bench but stall and moan when put back to work
had a Fuel Pump relay bypass switch fitted to prime a pump on a car that sat un-used ,(switch on for a dew seconds to prime ,then off to allow to relay to do it's job )
many cars fuel pump won't run without crank signal ,not good when the battery is being raped by the starter .
a generic pump is also an option ,done that a few times ,walbro or summat off ebay about £35 (check spec to match what's needed)
hope you get it sorted DG

[Kevin Wood]

Yep, likely the pump is still fubar. Once the internals get worn they will spin happily but struggle to maintain full pressure.

[Doctor Gollum]

Apparently Bosch do a direct replacement pump with housing, part numbers cross match with both Mercedes and VDO numbers on the original pump. Cheaper than a complete pattern pump/sender assembly, and two Omegas less than Mercedes want for a pump

Fingers crossed it turns up on Saturday so that I don't have to catch the train to work next week