I've been having a very hard time starting my 1989 190e 2.6. Takes a long time to start and when it finally starts it sounds like it wants to die (very rough idle). Pressing the accelerator causes it to die or move very very slowly and then die.

I have replaced the fuel pump relay with a brand new OEM one and the problem is still there. Checked amperage thru fuel pump relay which stays about 8.5A (it starts at 10A then slowly falls) for both fuel pumps.

The MB CD manual says that fuel pump nominal minimum voltage is 11.5V, I tested both fuel pumps (by pulling off fuel pump relay and shorting jacks 7 & 8): one is at 11.17V and the other is at 11.26V. They both make a loud buzzing sound when running.

I don't know much about cars and have very little experience with this, so I don't know if the 11.26V and 11.17V is close enough to 11.5V.

Before I buy 2 new fuel pumps, I want to know if these values are close enough or if the pumps really are bad (or about to die). Also, I have a fuel pressure tester but don't know how to use it (don't know if I need to do a pressure test as well and the voltage test).

So are the pump voltages good? Thanks.

I forgot to add that I tested the voltage directly across the terminal posts of each fuel pump; so my measurements do not take any wiring into account. Not sure if that matters...

Those values seem fine. I'm pretty sure you need a very special fuel pressure tester to test that car.

i did ran a 12v wire all the way to the fuel pump and see if it will actually run.
u should fuse it too, so u dont start afire, have extinguisher handy, u never know.
or have a friend stand by with F Ex ready.