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  #1  
Old 06-25-2014, 11:06 PM
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Do I need a new fuel pressure regulator (W124, M103)

RE: 1987 260E

Made the mistake of pulling on the vacuum line that runs from the valve cover gasket breather hose to fuel pressure regulator, and inadvertently pulled the mushroom shaped rubber fitting out of the end of the fuel pressure regulator.

Secured a new rubber fitting, but am not able to force it into the very small hole in the fuel pressure regulator.

The fitting is just way too big for that little hole.

Obviously, since the FPR is big $$$, I don't want to replace it just because of the rubber fitting issue.

Any advice?
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  #2  
Old 06-26-2014, 07:20 AM
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The vacuum line acts as a signal to the pressure regulator.
The amount of vacuum present will affect the actual rail pressure.

Low vacuum raises the pressure, which equates to more fuel going into the cylinder.

Something doesn't jibe WRT your description. It shouldn't be that diffucult to install the line on the regulator.


Jim
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  #3  
Old 06-26-2014, 10:23 AM
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On my W126, that hose is not a vacuum hose, rather it is a "vent" hose for the back side of the regulator.

There is a piston like thing which slides back and forth inside the regulator to adjust fuel pressure. And the back side of that needs to be open to the air so the piston can slide freely. Thus the "vent" hole.

The only thing is, a fuel regulator might at some point in its life leak. And if that happens, it would not be very good if it leaked fuel onto a hot engine. Thus the vent is connected to the engine crankcase via that hose.

(Measure the vacuum - none on mine! Because it goes to the crankcase.)

I would get a new fuel pressure regulator if necessary. Sort of like an insurance policy against a potential engine fire. Also that hose may keep dust and dirt from entering the pressure regulator (as it sucks in air).
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  #4  
Old 06-26-2014, 10:37 AM
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Thank you for both of your replies.

The rubber fitting that the local MB dealer spec'd for me was P/N 000-078-02-81.

One possibility is that the hole size in the pressure regulator changed during it's production life, and the parts guy at the dealer didn't make that distinction.

Until I have the problem sorted, I made an adapter and used silicon glue to hold the vacumm line in place in the fuel pressure regulator hole.

I am going to call my indi german parts guys when they open to see what a new Bosch fuel pressure regulator costs.
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Old 06-26-2014, 06:23 PM
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Found out the answer from the indi mb tech: the purpose of that vacuum line on the fuel pressure regulator is only to do one thing: vent gas into engine in event diaphragm ever breaks (just as Elektri said).

Went to Pick and Pull to pull a fuel pressure regulator. Guess what: it had the vac. hose glued into the hole in the fuel pressure regulator, just like mine is now.
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  #6  
Old 06-26-2014, 06:26 PM
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My bad.

For some reason I was thinking about the M119 in the 400E, not the CIS you have.

Jim
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