I have a 2008 Mercedes E350 that won't start.checked relay it's fine.I don't hear fuel pump coming on.can it be the emergency shutoff switch and if so where is the location

It could be fuel pompe problem or electro-valve don't work correctly

Are you hearing the pump run when you turn the key to ON? If not, you may need to reset the emergency fuel shutoff button. OR it might be a fuse or relay .
If you hear it run,it should prime right away. don-ohio (:^)

Well there is no shutoff relay, but there is a fuel pump relay that powers the pump.
I would check it first. The computer grounds the relay for 3 seconds when you crank the engine to boost fuel pressure. Once the engine starts the pump is powered only if you have oil pressure.

most likely you have a bad crank sensor or fuel problem you need to check fuel pressure ,if you have enough pressure ,most likely you need crank position sensor,if you don`t have fuel pressure ,it might be your fuel pump relay or the pump, i would start with the relay first very unexpensive. you can also hear the pump if it`s working by cranking the engine and listening rear of the car for a humming sound .
good luck

No noise from fuel pump when you turn over the car .First thing get voltage at fuel pump relay checked, is there 12 volt to the relay.If no, then problem is again the relay.--------- To reconfirm the problem, try other test, that is remove the relay and by pass the relay terminals with a jumper wire .Then with 12 volt external battery give power to fuel pump connector and see, if the fuel pump starts, then its clear that fuel pump relay is faulty.----------- Also other problem can be fuel pump inertia switch.If the inertia switch is faulty then also fuel pump will not start.-------- The fuel pump relay on a 1995 Ford Explorer is in the power distribution
box, in the engine compartment, driver's side near the firewall.----------
The fuel pump inertia switch is in the right front passenger area
it is below the dash but above the carpet in the right hand corner.--------
Its a push button type inertia switch.
--------
Fuel Pump Activation
When ignition switch is turned to START position, PCM operates fuel pump relay to provide fuel for starting engine. PCM senses engine speed and shuts off fuel pump by opening ground circuit to fuel pump relay when engine stops or engine speed drops to less than 120 RPM. When ignition switch is in ON position, EEC power relay is energized (contacts closed). Power is provided to fuel pump relay and timer in PCM. Fuel pump receives power through fuel pump relay contacts.
Inertia Fuel Shutoff (IFS) Switch
All models use an electrical interrupt switch in fuel system. During a collision or vehicle rollover, electrical contacts within inertia switch open, shutting off fuel supply to electric fuel pump. Fuel supply is interrupted even when engine is running.
A reset button is located on switch assembly. If electrical circuit trips, vehicle will not restart until switch is reset. Fuel system should be inspected before resetting switch.
IFS switch is located under instrument panel, near right side of transmission hump. ----------- If the fuel pump relay, the inertia switch and fuel pump all checked ok, and fuel pump is working with direct 12 volt source to fuel pump.Then problem relates to computer.The computer (power control module, PCM) is faulty and has to be replaced.--------- This will help.Thanks.Helpmech.

Could be a number of things. Start with the fuel pump relay. When your key is in the start/crank pos. it overides the relay as soon as you release the key to run possition the relay has to stay ingaged or the fuel pump will shut off. Also look in your owners manuel for impact or emergency fuel shut off switch reset.

Is the fuel pump inside the fuel tank? If, so, you could try disconnecting the wire harness at the tank, and hot-wiring the fuel pump directly to a 12 volt source, in the correct polarity of course! If the pump runs, your problem may be a fuel pump relay, or a wire problem or connector problem. If the pump does NOT run, post that info. There may be a way around the problem!

fuel shutoff switch is actually a fuel pump relay in the relay box under the hood, but it is not unusual for a fuel pump to work on and off before it finally dies. but it is a good idea to check the relay first.

try swapping it with the horn relay (if the horn works). pay attention to the direction the relay is in. on GM's, it's possible to put them in backward or even miss the connectors completely.

you also want to check for proper power and ground in the relay socket.

something is killing the relays poss fuel pump drawing to much amperage check pump with amp probe is pump noisey?

If you have the ignition in the on position remeber the fuel pump only runs for a couple of seconds unless the car is activley being started