Do I need a new fuel pressure regulator? - PeachParts Mercedes-Benz Forum

tinypanzer · #1 03-30-2009, 10:59 PM

While working on my car this weekend, I broke the brittle vacuum line going to the fuel pressure regulator.

When I fit a new hose in there, I decided to suck on it to see if it was sealing well. It wasn't. Depending on how I wiggled the nipple, it would intermittently leak air. Here's the lame part. I tasted fuel vapor.

Is a small amount of fuel vapor here normal, or is my diaphragm going south? Also, can I just replace the rubber nipple or do I need a whole new regulator?

1990 300SE (M103)

Thanks!!

Ivanerrol · #2 03-31-2009, 02:48 AM

That vacuum line coming from the fuel regulator is not a vacuum line per se. That line goes to the hose that extends from the valve cover gasket to the air cleaner.
The purpose of that tube is to overflow fuel to the air intake in case the regulator diaphragm goes faulty. (Fire preventative.)

I don't know if sucking on that tube would have been such a good idea.

If the diaphragm has had it you need a new regulator. (New one $$$)

hey_allen · #3 03-31-2009, 05:42 AM

Huh. I would have thought that a "pressure" nipple on a pressure regulator would be to manifold pressure reference the fuel pressure, adjusting for engine load.

Many makes do that, but MB is often different, just for the sake of doing it differently!

Ferdman · #4 03-31-2009, 06:50 AM

tp, from my experience there is no way to replace the rubber vent line on a fuel pressure regulator, and the plastic vent line will not fit into the remaining stub. A new Bosch FPR is around $375 online.

syljua · #5 03-31-2009, 09:29 AM

Quote:

Originally Posted by Ivanerrol

That vacuum line coming from the fuel regulator is not a vacuum line per se. That line goes to the hose that extends from the valve cover gasket to the air cleaner.
The purpose of that tube is to overflow fuel to the air intake in case the regulator diaphragm goes faulty. (Fire preventative.)

The line is there to regulate the fuel pressure in the rail
so that the pressure is at a constant level above pressure in the intake
(so that a set opening time of the injector will give the same
amount of fuel regardless of intake pressure). If the diaphragm goes
south, yes the fuel will be drawn to the intake, but thats secondary.

I made a video on checking the FPR last summer;
http://www.pvv.org/~syljua/merc/FuelPressureME.mov

This is for a M119, and I see now, that maybe the M103 FPR functions
differently?

br,
syljua

tinypanzer · #6 04-01-2009, 06:25 PM

I think it probably does act differently. By the way, nice video.

For one thing, the M103 is using CIS, not electronic injection. For another, the vacuum line goes to the breather hose between the valve cover and the air filter housing. As such, it doesn't get a signal that is representative of manifold pressure.

Ivanerrol said "I don't know if sucking on that tube would have been such a good idea."

I didn't suck very hard, just enough to see if there was a seal or not. There wasn't. It's not like I put a mityvac on it and sucked it down to nothing.

Upon examining it further, it seems like the rubber nipple is no longer sealing to the metal housing. It appears to pop in there much like a tire valve stem. I wonder if I can seal it up with some RTV or some other goop. Perhaps even rubber cement would work, or glue from a tire patch kit. At $400, it's worth a shot!

pawoSD · #7 04-01-2009, 08:02 PM

When I was working on our 300E a few months back I damaged that rubber nipple thing too....I just jammed it back in the hole as best I could.....seems to be fine....although it'd probably drool fuel if the diaphragm fails....but I have a whole spare fuel pressure regulator....with an intact rubber piece....so I should be ok.

pawoSD · #8 04-01-2009, 08:18 PM

Quote:

Originally Posted by syljua

The line is there to regulate the fuel pressure in the rail
so that the pressure is at a constant level above pressure in the intake
(so that a set opening time of the injector will give the same
amount of fuel regardless of intake pressure). If the diaphragm goes
south, yes the fuel will be drawn to the intake, but thats secondary.

I made a video on checking the FPR last summer;
http://www.pvv.org/~syljua/merc/FuelPressureME.mov

This is for a M119, and I see now, that maybe the M103 FPR functions
differently?

br,
syljua

What a beautiful video! I felt love and emotion for that engine!

The power of music.....wshew.

Well done.