Knukle Head

Forgive the short hand but Im trying to get to the point quickly out of respect.
06 ML500 would not start. Took to the dealer, was told fuel pump is the issue.

• I changed fuel pump but still no start.
• Noticed no sound from new fuel pump
• Went to back and removed /jumped Fuel pump relay (still no pumping from new Fuel pump)
• Took the old fuel pump and put it on battery out side the car (worked)
• Hooked the (drained) old fuel pump up to car but left it out side the tank so I could hear it well if it kicked on.
• While the relay jumper was in place, I added and extra ground to the pump. (still no pumping )
• Took the old pump to the Back of the trucked ran power from the relay slot to the pump (worked)
  
  I employed voltage meter (this is where it gets really weird)
  
• At the fuel pump connector (above gas tank) I get 12 volts
• But as soon as I connect it to a fuel pump (old or new) it drops to 0 volts !!???
• I locate the connector BEHIND THE RIGHT REAR WHEEL to make sure that it is clean/ reconnect (still observe voltage drop when plugging pump in )

My next step is to remove the fuse panel and check for lose/bad connections back there.

Any help/ experience is welcomed/needed.

paulg

Somewhere in the power wire that supplies the pump, there will be a Fuse/Connector/splice which is corroded and gone high-resistance.

If all assodciated fuses are clean, start looking for hidden connectors.

Alternatively, re-wire it to the fuse box and by-pass any problems. Use decenty thick wire...

paulg

Forgot to say you can measure the voltage ACROSS the live wire in the connector (from one side to the other, not to Ground) to see if the voltage is low when powered on. If the connector has gone high-resistance, there will be no voltage across it untill the pump starts taking current, then it will rise (maybe to 12V) which should indicte that you've found the problem.

ml3204me

I would check the fuel rail to see if you have fuel coming up to that point. New pumps may not make any sound when operating (from off to on)

check this video on how to do that: