The fuel pump in my 98 Mercedes ML 320 died last summer. I replaced it then, but now it's having issues. When I turn the key slowly, I can hear the pump kick in, but when the starter kicks in it shuts back off. The engine will start for 4-5 seconds, then stop. I've put my multimeter on the electrical lines, and it reads 5v on the gauge lines and 12 volts on the power lines... but only for those same 4-5 seconds. I've checked the relay and fuse and both look good.
Where else can I look?