The car:
1981 500SLC 107.026 with 117.960 "Euro" spec (standard K-Jet without lambda O2 sensor).

History:
Has been in storage since it moved from Europe to Australia around 7 years ago. I purchased it late last year and have been preparing it as a club car with a view to having it attend its first event next weekend.

The problem:
With low fuel level in tank (around 15 to 20 litres remaining - not low enough for reserve light) it suffers fuel starvation symptoms when driven. Will perform well including strong full-throttle accelaration but will suffer intermittent power loss (stumbling or even stalling) after braking or cornering.

What I have checked:
Drained and flushed fuel tank. Cleaned strainer in bottom of tank. Tried another fuel pump (used one from my 190E parts car). Replaced fuel filter. Checked small strainer at inlet to fuel dsitributor. Temporarily replaced fuel pump relay with jumper wire. Checked fuel pressures in line between fuel distributor and warm-up regulator (1 bar at cold start rising to 3.6 bar at normal operating temperature. Around 5.5 bar with line closed between fuel distributor and warm-up regulator). Checked distributor cap, rotor and ignition timing all OK.

Other observations:
Both original fuel pump and replacement become noisy after about 10 minutes operation (yet both reach pressures listed above). Engine runs fine until car is driven. Vigorous shaking of car (whilst stationary) can cause engine to stumble (or stall) and hot fuel pressure to momentarily drop back to 2.5 - 2.8 bar. Listening through tank filler it is possible to hear a sound like air being drawn into a vortex when this occurs suggesting air being drawn into strainer and pump. This is worse with less fuel in tank and can only be prevented with fuel gauge showing tank more than 1/4 full (at least 25 litres in tank). If fuel level is reduced to the point where reserve light illuminates (less than 15 litres) car becomes undriveable due to engine stumbling and stalling. I have also noticed an intermittent sound like a relay clicking in the passenger's footwell near fuse box (where all relays are located), although I believe I still heard this sound with the fuel pump relay removed and replaced with a jumper wire.

Any suggestions as to where I go from here? I am considering purchasing a new fuel pump due to those I have both being noisy even though they show good pressures. This will eliminate any doubts about the pump.

Thanks,
Greg

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107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.