new fuel pump & relay & car still won't run

I put a remanufactured fuel pump in and then I wasn't getting any power to it. So I went to the junk yard and found a fuel relay from another 300e, but it was a superseeded part number.
Now the pump kicks on but when I'm driving it stumbles every time you try and give it gas.
Could this be because of the fuel relay being an earlier superseeded part number than the one that was in the car.
Any suggestions, I'm stumped and still have a car that won't run