Date: Sat, 21 Jul 2007 05:17:54 -0400
Reply-To: Sam Payne <bungeegull@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Sam Payne <bungeegull@HOTMAIL.COM>
Subject: Re: fuel pump relief valve?
Mssr. Foss wrote:
<<I don't know why anyone would do this 'test' that you did. The fuel pump
was
just responding like it should.
In the over all scheme of taking care of your vanagon, I don't think this
was a wise thing to do, unless you intentionally are checking for
weakness.....like a hose clamp not tight enough or something like that, or
a
hose about to fail.
It just does not seem like a kosher, or safe, or wise thing to do, to go
pinching off fuel lines on a running engine. You could cause a problem
were
there wasn't one in the first place at all.
< btw, this is why I had to bail on this list a few years ago - I see some
of the most amateurish, uninformed things here. It IS very educational
though, thanks for that ! ....learning what people 'make up' in their minds
to do on vanagons - and I don't mean to be harsh, but it is scary at
times !
)
smiles, Scott
www.turbovans.com >>
Scott,
That's done it, you've wounded my amateur, uninformed pride!
I did the pressure relief test on the basis of two books:
1.) The Bentley shop manual for a Saab 900, because the pulsed Bosch
Jetronic 2.4 FI system I'm running my engine with came from a Saab. The
Saab Bentley manual is much, much, much more complete than the Vanagon
Bentley, and lists the pressure relief test as a standard test. The '86-
'88 fuel pumps were roller type, like the vanagon, but were mounted in the
top of the tank (i.e. usually not submerged in fuel) and fed by a small
supply pump. This difference made me hestitate and look at another book...
2.) How to Understand, Service and Modify Bosch Fuel Injection Systems,
by Charles Probst, SAE. It's an excellent book, very clearly written,
covers pulsed and continuous FI systems, including the Digifant system.
The 'Pulsed Injection--Theory' section has a couple of good drawings
of Bosch roller-type fuel pumps, complete with a description of their
operation. The relief valve is shown, as is the check valve which holds
pressure in the system after the pump shuts off. No pumps without relief
and check valves are mentioned for any kind of Bosch FI system, including
continuous systems. The text: "The pressure limiter opens and directs fuel
back to the tank if fuel pressure in the lines goes over a limit. High
pressure fuel is delivered through a check valve, which closes when the
fuel pump stops to hold pressure in the lines."
And a quote from the Saab manual: "The fuel pump contains a bypass
valve to prevent high pressure from damaging the system if there is a
kinked or blocked fuel line. Also, there is a check valve at the pump
outlet to hold pressure in the system after the pump is turned off."
I did the pressure relief test because I had poor fuel delivery, it's
specified in the Saab manual and the valve itself is described as standard
equipment for all pulsed Bosch systems, including Digifant. Since I have
often found that the Vanagon Bentley is incomplete (no residual fuel
pressure test specified in mine, for example), I didn't worry that the
test wasn't specified there. I jumped the pump relay so the engine wasn't
running, and used a c-clamp to pinch off the return line so it closed
gradually. I meant to release the pump at 83 psi as specified in the Saab
bentley, But by the time I got my thumbs working together it hit 100 psi.
No leaks found afterwards.
One more note: the diagrams of the relief valve in the Probst book
show it inside the pump housing (with the check valve). As I understand
it, when the relief valve opens it allows the fuel being pressurized by
the roller cells to escape back into the supply (tank side) line, so the
pump just sits and spins in a bath of fuel until the valve closes again.
This is why no separate line is needed to vent fuel from the check valve
back to the tank.
I don't know for sure if the vanagon pump has a relief valve, but I'd
bet it does. Without one, if a return line got kinked or plugged and
pressure blew hoses off or burst them fuel would spray all over. Bad
Juju!! Joel Walker's post suggested the max pressure might be 120 psi,
and he added some good links. Testing to 100 psi is good enough for me
since I only need 83 max, so I'm done testing (and quite comfortable and
happy to have done it!), but I'm still curious. Anyone know? Check valve??
Sam
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