Sounds like you already checked for spark and it passed, if you have pressure gauges I would check the pressure at the fuel distributor, that would tell you where/if the fuel is losing pressure somewhere in the line. If your car has dual fuel pumps (I'm not sure on the w126, I know on the w124 they switched around 1990) perhaps one of them has gone out and the other is still working, giving enough pressure to start but not enough to sustain the engine running, and you would hear the system kick in still from the one pump. I caution you, that is just me thinking off the top of my head - I would still perform a pressure test.

If your fuel filter hasn't been changed in recent memory (say 15-20k miles), its probably a good idea to put in a new one anyway, since it is niether expensive nor difficult and is a maintenance procedure.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth