"Vacuum advance" on injector rail

I have a car fitted with the Bosch LE3-Jetronic system.

Between injector 2 and 3 on the fuel rail, there is a gadget that
looks like a vacuum advance device, as found on top of the
distributors of certain carb'ed engines.

What is this device for? What does it do?

I don't think that it actually serves to advance timing, but perhaps
it acts as a breather?

On 19 Jan 2004 06:10:39 -0800, (Jason Purcell)
wrote:

>I have a car fitted with the Bosch LE3-Jetronic system.
>
>Between injector 2 and 3 on the fuel rail, there is a gadget that
>looks like a vacuum advance device, as found on top of the
>distributors of certain carb'ed engines.
>
>What is this device for? What does it do?
>
>I don't think that it actually serves to advance timing, but perhaps
>it acts as a breather?


A lot of fuel pressure regulators look like a vacuum advance so that
would be my guess.

In article > ,
(Jason Purcell) wrote:

> I have a car fitted with the Bosch LE3-Jetronic system.
>
> Between injector 2 and 3 on the fuel rail, there is a gadget that
> looks like a vacuum advance device, as found on top of the
> distributors of certain carb'ed engines.
>
> What is this device for? What does it do?
>
> I don't think that it actually serves to advance timing, but perhaps
> it acts as a breather?

Ever heard of a phenomenon called "water-hammer"? Usually, you see it in
houses - Open a tap. Let it run for an arbitrary amount of time. Now
close it, QUICKLY. Chances are good that unless the house plumbing has a
water-hammer prevention device, you're going to hear a "SMACK!" from the
pipes. That "SMACK!" can be enough to literally blow pipes wide open.
It's the inertia of the flowing water hitting what amounts to a brick
wall. Since water can't be compressed, the energy has to go someplace,
and that someplace is either "into the air as noise", or "out through
the freshly busted-out hole in the pipe as a spray of water".

My bet is that your device on the fuel rails is the
gas/diesel/whatever-fuel equivalent of the house's water-hammer
prevention device - A place for the flowing liquid to dissipate the
energy of the flow when the orifice it's flowing thorugh is closed
quickly. If you were to disassemble it, (if that's even possible) I'd
imagine you'd find a diaphragm separating atmosphere from fuel inside an
"expansion chamber" type setup, and a calibrated hole to let the
pressurized air escape, or be sucked back in as the pressure drops.

In a house, the same effect is achieved with a special section of
(usually vertically mounted, typically about 3 feet tall and an inch or
so across) sealed pipe containing a more-or-less permanent air-bubble.

In a way, it *COULD* *KINDA* be thought of as a breather. More accurate
would be to call it a pressure-relief, but even that isn't a perfect
name for it.

--
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I think Don's argument is more plausible.

I have a fuel pressure regulator, and that's not it.

Thanks a lot for the help guys!