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My car has stalled an wont start so I replaced the fuel pump

ran good for a day...
My car has stalled an wont start so I replaced the fuel pump ran good for a day or two but today after driving it 4 miles it stalled again and would not start. I jacked it up to change the fuel filter and tried to start and it started. I went ahead and changed the fuel pump anyways. I put a pressure checker on it it has 0 pressure with key on but starts fine and pressure goes up to close to 60psi. Should I have pressure with key on and engine not running
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Answered in 7 minutes by:
10/14/2017
David Craig
David Craig, Auto Mechanic
Category: Mercedes
Satisfied Customers: 4,176
Experience: Owner/Mechanic at 3D Automotive
Verified

Hi Im David, thanks for visiting the site. yes the fuel pump should run for about 5 seconds when the key is turned on

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Customer reply replied 1 month ago
What should the pressure be with the key on and engine off be?

standby please

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right around 48

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Customer reply replied 1 month ago
The fuel pump works fine when runing but no pressure just with key on what could that be then. The car is runing great again it just scares me having 0 pressure when i just turn the key on without starting it. I guess its not priming?
Customer reply replied 1 month ago
but it starts immediatly when I releive the pressure at the schraider valve and restart
Customer reply replied 1 month ago
I just went out let the pressure out down to zero truned the key back on still 0 pressure waited 2 minutes to see if there was a delay still 0. cranked it and it started immediatly pressure shot up to about 58.

very strange. pull the fuel pump relay out. do you have a voltmeter?

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Customer reply replied 1 month ago
Is it possible this car primes upon starting?

no

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pull the relay and check terminal 86 for voltage with the key off.

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Customer reply replied 1 month ago
Not sure Im checking the right slot but one shows 0 and the other reads 12.45 I paid for you to call me not sure if it wenbt through

cant call right now. you wont be charged if I dont call. there should be 4 slots

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should be 30,87,86,85 is the relay numbered on the bottom by the prongs?

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Customer reply replied 1 month ago
That one shows 12.34 which is the first big slot

is the key on?

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Customer reply replied 1 month ago
no

ok, thats position 30 then. now turn the key on and check for voltage in a different slot

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Customer reply replied 1 month ago
None in any other slots. That is with the relay out

correct. with the relay out. you should get 12 volts in another slot with the key on. thats the prime voltage

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Im not sure whats going on here. Let me open this up to the other techs to see if they have any input. please do not reply back or it will take the question off of the board

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Marty
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 54,297
Experience: Bosch Certified Master Tech. Over 35 years experience.
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Hi, perhaps I can help. My name is***** fuel pump on this car only primes one time per start cycle. If you don't start the car the pump will not prime again. Since the car starts and runs you have nothing to worry about. If you want to test the system try starting the car then bleed off some fuel pressure then turn the key on and you should see the pump give an initial prime. If the car continues to stall with the new fuel pump installed I would suggest that you replace the crankshaft position sensor. The sensor is known for causing intermittent stalling on this model.

Let me know if you have any questions.

Marty

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Customer reply replied 1 month ago
I started the car then took key out released the pressure tighten back up and not pressure on on position but fires right up. I have replaced the CPS but that symptom was a little different after stalling it would still kind of start sputter and turn off. This time it just cranked and the car was cold. Not sure if this means anything but when I jacked up the car a little replace fuel filter/regulator I tried to start one more time and it did. I know these cars have a pumpon the passenger side and a float type system on driverside could that have been sticking and when I jacked it up it wiggled it loose? Or am I grasping lol

I think your grasping a bit :-)

Sometimes when the pumps are failing they will not push the fuel from one side of the tank to the other and they will run out of gas on the pump side of the tank. Since you have a new CPS and a new fuel pump I would just drive the car and see if it acts up again.

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Customer reply replied 1 month ago
But it stalled today which was after I installed the CPS and Pump a month ago. So I figured I would change the fuel filter that is the only new thing I did today. Is it possible that the fuel filter regulator was going bad? I replaced it only a year ago when I gave it a tune up
Customer reply replied 1 month ago
The car has less then a 1/4 of a tank and I think last time it happpened when I changed the fuel pump it was close to empty does that help at all
Customer reply replied 1 month ago
Also I remember more now it did start at first until I added more gas to it after I replaced the pump. Maybe the other pump is not pumping it back to the fuel pump side correctly?

It's possible that the regulator was failing but it would be rare. If the lines in the tank are not properly attached or are kinked they can affect the ability of the fuel to transfer from one side of the tank to the other. It would be more of a problem when the tank is low. Rather than pull the pump and sending unit out again I would fill the tank about 3/4's full and see if it still stalls. Keep your fuel pressure connected so you can see if you are losing fuel pressure if it stalls. I have had problems with cheap aftermarket pumps.

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Customer reply replied 1 month ago
Okay I will check the lines its not much trouble pulling the back seet cover and inspect all lines maybe one is failing. How do I pay you?

You just need to click on a rating for my service in order for the website to credit me for helping you today.

Marty
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Category: Mercedes
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