I have a 1997 E320 Mercedes Benz that idles very rough and sometimes backfire when first starting for about 5 minutes. At times the will not run faster than 20 mph and is very sluggish on take off. I replaced the fuel pressure regulator and ran a pressure test on the fuel line, which was at 45 pounds, is that within spec? After installing the new pressure regulator the car cranks and dies within 3 seconds. Is there a fuel pump relay on this car and if so where is it located or could the problem be within the cat converter.

I need help please advise.