Date: Mon, 21 Jul 2008 18:10:23 -0700
Reply-To: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Subject: Re: 2.1 WBX stumbles after hot restart; vapor lock?
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hi,
yes, almost all fuel injection systems have the fuel traveling in a loop ,
to the engine and back to the tank, and the engine takes off what it needs.
This keeps the fuel from absorbing a lot of heat while it's near the engine,
and returning it to the tank has somewhat of a cooling affect, or
temp-stabilizing affect.
it also operates in the 30 to 34 or psi range, so that helps prevent vapor
lock.
When the engine is off of course, the fuel sitting in the fuel lines on the
engine can pick up heat, if things are hot, as there's no circulation then.
I saw the guy's post suggesting that perhaps water has gotten in the fuel by
condensation and low fuel level. That's possible, especially in high humitdy
areas, though not likely, but it is on the list of things that must be
considered.
People, even shops, seldom ever consider the fuel itself.
And water in the fuel falls udner that. I sort of have this rule to always
empty out the fuel filter backwards and see what's in there.
Comparable to always checking the fuses first for *any* electrical problem.
I use 'substitue and bypass' a lot for a diagnostic strategy. If I think
the fuel tank itself is a factor - restricted pick up say .........
I just rig up anohter aux. fuel tank quickly. I keep a marine tank and
hoses around just for that. That allows me to test with a differnt fuel
source, and different fuel than what's in the tank. I recongize it's not
that easy from most home technicians to rig up though.
as for 'something to go on' ............that's why I suggested rigging up a
fuel pressure guage temporily. I had a vanagon last winter that would just
do into 'will only go 10 mph' mode, and only sometimes. . We rigged a fuel
press. guage - sure enough , when it acted up, fuel pressure was low.
So that gave us the info it was fuel supply and fuel pressure related, and
not the electronic fuel injection or ignition systems.
and the fuel filter, even if it's been on there only say two
weeks..........it's still a valuable diagnostic thing - to see what's in
there.
There is a tendency to think 'it can't be that, that's new' .............
I go the other way - "something's been worked on ? - that's where I look
first ! "
it would be nice if you found water droplets in the fuel from the filter -
that would offer a good explanation for the symptom you're having.
we always love it when we find an 'ah ha, this is IT !" ......so nice when
that happens.
Diesel fuel filters are designed so water will collect in the bottom of
them - there's even a drain on the bottom of them, and they are mounted
vertically.
not so in gasoline. Water and gasoline don't mix very well. One way to
treat gasoline that you know or think has water in it is to add a
water-absorbing fuel filter , which is alcohol............'isopropl' I want
to say. Alcohol mixes with water in ANY ratio...........and quite
well...........and the idea there is that it picks up the water in the fuel
and keeps it mixed in the gas so it can get burnt in the combustion process.
I'm not convinced at all that this is a fuel problem.........I think it
started with you asking if it could be vapor lock.......and water condensed
in the fuel has been suggested - I woudl say 'those fit the
symptom'.........but that is not a diagnosis, just something to consider and
test for, for sure.
it's a nasty struggle, but it's possible to repair or replace that vent line
with the tank in place.
very early ones - the larger line across the tank, are metal too. Metal
gives way to plastic as cars evolve. I'm sure they are working on the
plastic engine. They already have plastic vavle covers and intake
manifolds.
let's us know what you find.
about aux tank for testing.......
well, I was gonna tell ya how to rig up a gas can to run the engine off of
..........but it's messy, and the pump sort of needs to have a
prime...........and fuel hose sizes are odd at the input to the pump
...........but that would be a intersting test- to see if it does it off a
completley indepedent fuel source.
I find that sort of 'substitute and bypass' startegy to be VERY effective in
nailing down what is always............
really.............."just a blockage or leakage of fluids or electrons."
( and I don't think all people relize that 'fluids' also mean air, exhaust,
vaccuum etc. , not just liquids. )
scott
turbovans
eager to hear your good progress.
----- Original Message -----
From: "Allan Streib" <streib@cs.indiana.edu>
To: "Scott Daniel - Turbovans" <scottdaniel@turbovans.com>
Cc: <vanagon@GERRY.VANAGON.COM>
Sent: Monday, July 21, 2008 5:13 PM
Subject: Re: 2.1 WBX stumbles after hot restart; vapor lock?
> "Scott Daniel - Turbovans" <scottdaniel@turbovans.com> writes:
>
>> how much junk was in the old filter when it was changed ? you can
>> get very useful information checking the contents of a fuel filter
>> when you change it. empty it out backwards on a clean dish or
>> something similar.
>
> Tossed it. Didn't think to perform an autopsy on it.
>
> I was just looking at the procedure to remove the tank, and for the
> Digifant it seems there is a return line which indicates that the fuel
> system is a loop -- therefore vapor lock should not happen? I suppose
> there could be some vaporization in the lines in the engine
> compartment, which could cause some hesitation for a minute or two?
> Sound plausible? Or is something else going on?
>
> Someone suggested a bit of water in the fuel. Again possible, it's
> been sitting with a low fuel level for a while. But wouldn't the
> filter grab that?
>
> Allan
> --
> 1991 Vanagon GL
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