Jumper the fuel pump relay and see if it persists. If not, replace the relay (behind the passenger side kick panel, top one in column of three, front side, I think). Variable fuel pump sounds is probably intermittant operation from bad electrical supply OR a bad ground -- chase down the ground wire and make sure it's not corroded.

Have you run a bottle of Techron through it yet? These systems are notorious for getting sticky from old fuel, the injectors could be cutting out.

I'd also pull the cap and check the points for crud, they tend to get dirty fairly easily. Clean with some linen paper of a new dollar bill by opening by hand, inserting paper, pulling about a quarter inch or so, then opening again to remove paper. If you just pull it out, you tend to pull shreds off the sides and hold the points open. Carb or brake parts cleaner works, too.

If that doesn't fix it, it's an intermittant electrical connection or the trigger points in the bottom of the distributor, pull dizzy and points and clean with brake parts cleaner (make sure it doesn't contaim methylene chloride, that will melt the plastcs!).

I would also check the tank for crud -- its' possible that the screen is plugging.

Fuel pressure in the main (before the regulator) should be 29.5 psi.

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!