Re: E30 320i fuel pump replacement

This is really sounding very much like my experience except that mine only
took several months to evolve into something that I could diagnose instead
of several years like yours. It will all make perfect sense once you see
the inside of the pressure regulator.

I will try to describe the innards of the regulator.
Imagine a vertical piece of 3/16" ID metal pipe -- this is the overflow back
to the gas tank out the bottom and the top is covered by a round flat disc
that blocks the exit. This disc is attached to a rubber diaphragm that will
lift the disc off the end of the overflow pipe when the correct pressure is
reached. The outside diameter of the rubber diaphragm is sealed between the
two chambers of the housing. In the upper chamber of the housing is a
compression coil spring that preloads the disc onto the end of the overflow
pipe. The lower chamber of the housing is connected to the fuel rail and is
full of fuel at the regulated pressure. The upper chamber has a port that
is plumbed to manifold vacuum so as to subtract the manifold vacuum from the
spring pressure. As fuel is pumped into the system the pressure rises until
it is enough to overcome the spring preload and raise the disc up off the
overflow pipe thereby sending excess fuel back to the tank.

The peculiar behavior of this malfunction occurs because the way the
regulator disc is attached to the rubber diaphragm allows it to become
disconnected when the fuel pressure is high and then to reattach itself when
the engine is turned off and the spring pushes the diaphragm back down onto
the disc. The disc has a small sphere the size of a bb welded onto it's
upper surface. This ball is held to the diaphragm by a thin sheet metal
inverted cone that is part of the diaphragm. The cone has slits on all four
sides as a way to form it around the ball after the ball is welded to the
disc so the 'leaves' of the cone are springy. After many years wear of the
ball and the leaves of the cone make it possible for the fuel pressure to
pull the ball out of the cone so that the regulator no longer works and the
pressure goes sky high. After the engine is turned off, the pressure goes
away, the spring pushes the diaphragm back down, and the ball snaps back
into the cone -- perhaps at a little different clocking so it may stay
attached for some time.

In the beginning my car would only stall at idle once every week or so and
would always start right back up and be fine for another week. At the end
it would run OK for 15 minutes in the morning and stall at every stop after
that. I finally put a fuel pressure gage on it and ran it for 15 minutes so
I got to see the pressure shoot up to over 100 and my fuel hoses all try to
straighten out.




"Al" <alnews67@xxxxxxxxxxx> wrote in message
news:Xns999FBBEE1CA1Balnews67hotmailcom@xxxxxxxxxxxxxx
This sounds like a failure of the fuel pressure regulator.

Exactly what I thought, but disconnecting the return hose shows a healthy
flow of returning fuel. Maybe it's not enough - Difficult to tell.

A bit of history - A had the same fault (same car) a few years ago. Local
garage (non BMW) declared the fuel rail pressure to be around 32-34psi,
i.e. normal. The fault just went away after a while and the car ran
perfectly for a couple of years!

I had this happen on
my '84 318i a few years ago. Leaks started showing up at every hose
clamp

This time the leak was at the bulkhead end of the fuel rail - A very nice
spray that went everywhere :-( Remade the connection, moved the hose clip
up a little and promptly blew apart the coupling from the fuel filter to
the fuel rail :-)

and the engine would barely run at low throttle settings --
wouldn't run at all at idle.

Seems to be the same problem. I work around it by putting a resistor in
parallel with the temperature sensor, which fools the ECU into giving
shorter injector pulses and the engine runs fine (apart from being
difficult to start of course).

Maybe I'll just take a chance and fit a new FPR - It will cost more than
the car is worth though ... ;-)

Cheers,

Al.


.

Relevant Pages

  • Re: weedeater carburetor: how does it work?
    ... the needle valve diaphram is only connected to the primer bulb. ... diaphragm and spring arrangement is a pressure ... From there the fuel flows ...
    (rec.autos.tech)
  • Re: Solenoid Valve
    ... pressure and "controlled leaks" to operate the valve. ... a fuel cell system, for example. ... Direct acting *diaphragm* solenoid valves do not exist. ...
    (sci.engr.mech)
  • Re: 92 Explorer floods and backfires
    ... Fuel injectors are designed (rather, physics has made them design fuel ... injectors) to work at a specific pressure drop across the injector nozzle... ...
    (rec.autos.makers.ford.explorer)
  • Re: Hotsy Pressure washer questions
    ... Beware the pressure side-an old machine may be weak and have corrosion or fatigue damage...don't want to hot-wash your face... ... A fuel oil burner has a VERY narrow A/F range, and atomization, turbulence, temperature of the combustion chamber, and the character of the blower air flow all affect combustion. ...
    (rec.crafts.metalworking)
  • Re: Further on "Rockets not carrying fuel."
    ... > possibility of piping the fuel up to a rocket during ascent rather than ... > carrying the entire fuel load from the beginning of the trip. ... > density low at high pressure by making the temperature high. ... > need the high efficiency that a liquid hydrogen/liquid oxygen engine ...
    (sci.astro)