If the primary pressure regulator were defective, could that be a potential blocking point?

Also FWIW (for what its worth) if you drop gas down the pipe (air flow sensor) it fires right up. Not the lumpy bad gas, fouled injectors, crap plugs kind of a mine field, but the firing on all eight ignition that tells me that this car will run well if it gets some fuel.

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1981 300TD
2005 C55
2004 E500
1999 ML430
1992 400E
1998 C43
2001 SL500
1988 300SEL
1986 190E 16V
1991 190E 2.6