fuel pumps kep running 300te w124

ig_Al_300te

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Hi People,

Just a quickie ;)...should my fuel pumps keep on running with the ignition on or should they just prime and shut off?:confused:

Its just that I can hear that they dont shut off just keep on running and it is quite hard to start not on the button as you would expect from a fine german piece of engineering:)

Thanks
Alex.
 

jibcl500

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They should prime and **** off , Would guess the fuel pump relay to be at fault.

jib
 

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They should not run all of the time,, has the relay been removed and the pins bridged
 
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ig_Al_300te

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none of the above....

FPR changed two months ago when i had another problem no pins bridged..someone said it COULD be the accumulator but don't like changing parts willy nilly

thanks for the quick reply's guys!

Alex.
 

Mercedes 190E

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none of the above....

FPR changed two months ago when i had another problem no pins bridged..someone said it COULD be the accumulator but don't like changing parts willy nilly

thanks for the quick reply's guys!

Alex.

Pretty sure it isnt the accumulator if it's running constantly. A faulty accumulator would just run it for a bit longer than usual....
 

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What year is the car please
 

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The pressure reducer just returns the surplus fuel,back to the tank,, what happens if you pull the relay out,,if it stops or will not run, then the relay must be short circuit
 

kth286

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I was thinking that the fuel must just be running full circle back to tank and not holding pressure in the system, hence difficult start.

Fuel pressure regulator has a spring loaded diaphragm for controlling pressure and excess is returned to tank; and it has a check valve that works in conjunction with the accumulator to maintain fuel pressure for starting.

So, in conclusion check the fuel pressure regulator is fully OK and also the accumulator.
 

Alex Crow

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that would not explain the pumps running constantly, it is most likely to be the fpr. it should run briefly to prime with ignition on, run constantly with starter energised, and run constantly with >300rpm or so. all this is controlled by the fpr.
 

Number_Cruncher

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I fully agree with AP's post.

There's no pressure sensing* of the fuel acting as feedback to switch the pumps on or off, so the accumulator and primary pressure regulator make absolutely no difference to how long the pump runs for.

* There's no fuel pressure sensor anywhere in the system.
 

Alex Crow

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nor on any newer petrol systems that i have worked with so far...
 

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I have already asked him to remove the relay to see if the pump still runs,, its possible that someone before him bridged the pins
 
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ig_Al_300te

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Well that is strange..

like you guys suggested to remove the FPR the car continued to run and would re-start without the FPR in place?????????

Looks like Im gonna have to do some digging around her to see what has gone on as the current situation is dangerous in a crash situation ( Not that I intend to stuff her mind!)

Thanks
Alex.
 

Number_Cruncher

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I have already asked him to remove the relay to see if the pump still runs,, its possible that someone before him bridged the pins

Yes, that's a seriously dangerous modification, and if this bodge is found, the relay should be repaired properly.

By cutting the supply to the fuel pump if no ignition pulses are detected, the relay prevents fuel being sprayed about in the event of an accident, and thus performs a vital safety function.
 
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ig_Al_300te

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Thinking on......

I'm wondering if the LPG conversion has had something to do with this????
 
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ig_Al_300te

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Yes, that's a seriously dangerous modification, and if this bodge is found, the relay should be repaired properly.

By cutting the supply to the fuel pump if no ignition pulses are detected, the relay prevents fuel being sprayed about in the event of an accident, and thus performs a vital safety function.

Yeah I dont like the idea of it either!!:confused:

Thanks for the quick reply N-C:)

Alex.
 
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ig_Al_300te

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I have already asked him to remove the relay to see if the pump still runs,, its possible that someone before him bridged the pins

Hi Malcom,

Deffo no bridged pins as i had the FPR and socket out the other month when the FPR and metering head had a wobble and the wiring was untouched there so will have to have a look in the fuse box to see if the bodge-a-McCall-it is there.

Thanks
Alex.
 


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