Please Help with 88 300E

My 88 300E with 105000 miles developed a serious problem. A few weeks ago it started to stall a few seconds after I would start the car. If I waited a few minutes, it would run for a few miles and then stall again. Now, I am only able to start it and after about 20 seconds the engine stalls and after few seconds after this, the fuel pumps stop. I changed the catalytic converter before the problem developed and fuel pump relay after the problem persisted (did not help). I really do not know what to do... Is there another relay that could go bad? Are the fuel pumps bad (got two inline) or fuel filter or what else? Any advice would be greatly appreciated...