Thank you, 97 SL320.

So, is it possible that one of the fuel pumps is working enough to cause an audible fuel swishing sound at the fuel distributor....but, because the OTHER (2nd) fuel pump is not working and therefore not building up enough pressure (100 psi) to reach the proper psi to fire the injectors?
I get a small squirt of fuel when the fuel-line fitting is cracked, after presurization, but not much.

I guess that might mean that at least the accumulator is working then?

And maybe one fuel pump is bad? ...then...,one pump is good, which is why it sounds like it's working? I can test them individually,now that they are out of the car. I will wait until some of the fuel fumes clear before sparking up the battery charger. Stale fuel really stinks!

I can see now how each post on the pump is marked pos. and neg.

So, 12 volts to the pos. post.?

Does that fuel distributor need to be at a constant pressurization to work, then? Is that right? I don't know?

Does the accumulator keep the pressure constant during the pulsing from the injectors constantly firing off some of the pressure?

Then would the fuel pressure regulator keep certain that only 100psi goes to the distributor?

Is the f.p regulator the small can (similar to the accumulator, but smaller) up next to the fuel distributor itself?

I was also reading about these check-valves located at each end of the pumps....I wonder what would happen, if one of those check valves stuck closed? How are they tested?

What is the purpose of the check-valves at the fuel pumps?

Is there suppossed to be 2 of those c\valves then?

I can see how they are piggybacking one pump, to the other, "supercharging the psi, as you said above". It is obvious the way they are plumbed, makes sense, now that you mentioned it.

What are the insides of these fuel pumps made of? Could we bench test them and run some marvel mystery oil through to wash the varnishy fuel out of them?