Date: Fri, 4 Jun 2010 12:48:12 -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: Upstream Fuel Filter dissection results
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hmmmm...
EFI fuel mixture is determined by how long the injectors are held open, and
the fuel pressure behind them.
So I suppose, in that sense low fuel pressure will affect mixture.
If the oxygen sensor is working and it's in closed loop, there is some
mixture correction feedback of course.
low fuel flow itself won't affect mixture per se, too much I don't think.
You'd have low power if you had low fuel delivery rate.
my hunch is the inner diameter of the smallest part of the fuel supply
circuit does not have to be too big.
There are two sizses of fuel outlet on the 2WD vanagon fuel tanks...
some are the size a 5/16th ID hose fits on.
Others...like an 87 2WD van have a larger outlet, like 7/16th inch.
sometimes when you get an aftermarket tank, and you had the bigger outlet
before, now you have the smaller one.
I built a 97 DOHC 2.5 Subaru engine conversion, and at first we had a clear
cut off at 4,200 rpm ...
and we wondered if it was the smaller fuel outlet on the tank, cause that's
what it had, rather than the bigger one.
that turned out to be lack of a good Vehicle Speed Signal,
so there was that 165 hp, 6,200 rpm engine, running just fine off the
smaller fuel outlet at the tank ...
my point is,.....that small size is enough for good engine power and proper
mixture..
and mixture is more related to fuel pressure, than to fuel delivery volume.
Scott
www.turbovans.com
----- Original Message -----
From: "Don Hanson" <dhanson928@GMAIL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Friday, June 04, 2010 7:04 AM
Subject: Re: Upstream Fuel Filter dissection results
> I don''t have any measurements or real numbers on flow rate or diameter
> on
> my installed Moto fuel filter..but it is substantially big, compared to
> most
> aftermarket filters you see listed in cats or at the FLAPs.
> My thinking, and I may be "old school" for thinking this way, is that if
> your standard Bosch filter was dirty and the output restricted, the engine
> might be forced into running lean, which is not so good for motors.
> However, with Electronic Fuel Injection, maybe the "brain' would know
> enough
> and compensate the mixture if the fuel source got restricted, and you
> would
> get an 'error' message.. I know it doesn't take long to seriously damage
> an
> engine running lean, so I would hope the EFI Brain would be 'on top of'
> telling you your fuel filter was partly clogged.
>
> With a carburetor motor you would have to rely on your instruments to
> detect
> a lean condition.
> Anyway, I can usually hear the FP in my van and I make a point to listen
> when I start up. I listen to see if it sounds normal. Probably would not
> sound right if it were sucking air.
>
> Don Hanson
>
> On Thu, Jun 3, 2010 at 10:46 PM, Peter DiFalco
> <peter.difalco@gmail.com>wrote:
>
>> As I recently learned on the list when I opined in a similar vein,
>> insufficient fuel flow to the pump due to an upstream filter, perhaps a
>> clogged filter, causes cavitation in the pump and may ultimately harm it.
>> So
>> maybe VW thought it was better that a few things flowed through the pump
>> than that the pump work so hard to pull fuel through the filter. I'd be
>> interested to hear how it goes with the extra upstream filter you and Max
>> have installed.
>>
>> -Peter
>>
>> On Thu, Jun 3, 2010 at 10:07 PM, Don Hanson <dhanson928@gmail.com> wrote:
>>
>> > I just did my 'maintainence' under the van, too. I added an inline
>> metal
>> > filter, from a Triumph MC actually, between the tank and the pump inlet
>> > because I had it and because the fuel pumps are costly to replace and
>> > the
>> > filter isn't...I think maybe $15 or so...probably much cheaper if it
>> didn't
>> > say "Triumph" on it... I didn't cut open my bosch filter but I did put
>> > about 120 psi of air into the outlet and blow it onto a white paper
>> > towel....no chunks no grit came out.
>> > I checked all my one year old fuel line and it looked perfect still.
>> > I
>> > didn't replace my (jetta 1.8l inline) fuel rail with the metal one I
>> > have
>> > waiting, yet.
>> > I dunno why VW put the filter down stream of the fuel pump in the
>> > first
>> > place...but I bet someone will tell us.
>> >
>> > Don Hanson
>> >
>> > On Thu, Jun 3, 2010 at 7:08 PM, Max Wellhouse <dimwittedmoose@cfu.net
>> > >wrote:
>> >
>> > > I've been using a 1/2" gas valve shutoff upstream of my upstream fuel
>> > > filter for several years now to make th upstream and downstream
>> > > filter changing a little less of a hassle. It also makes a decent
>> > > cheapy theft deterrent if you park in nasty neighborhoods.
>> > >
>> > > Last night I pulled the upstream filter and the downstream filter for
>> > > annual replacement and decided to see what they had caught in a
>> > > year's
>> > > time.
>> > >
>> > > The downstream filter was made in Poland and I think I bought it at
>> > > an AutoZone or Advanced Auto, so I doubt that it was a Bosch. It had
>> > > an aluminum housing as opposed to steel. It had it's share of dark
>> > > colored stuff, but no chunks of rusty gas tank or anything like that
>> > > further supporting my theory that an upstream filter is the best
>> > > protection you can give your fuel pump other than keeping from
>> > > running the tank dry trying to make the next gas station.
>> > >
>> > > Since my 90 GL: didn't have an upstream filter in it to begin with, I
>> > > put a metal in line filter from WIX in there that had male 1/2" barbs
>> > > on each end. Current part number is 33248. There's a 5 in front of
>> > > those 5 numbers, but the local parts guy told me that the first
>> > > number simply denotes where the filter was made. They make a plastic
>> > > one too in the same configuration, but I don't have that number
>> > > handy. Paid like $11 for the metal one and the replacement Bosch
>> > > filter for the downstream side is likely the spare I got from Bus
>> > > Depot some time ago.
>> > >
>> > > Cut the Wix apart first as my 2 wheeled pipe cutter jaws were just
>> > > slightly too small to open it up that way. I unfolded the filter
>> > > media and to my surprise there were no rusty chunks of gas tank in
>> > > there. What was curious though, was all the dried grit stuck to the
>> > > circumference of the inner metal walls. Sure glad all that didn't go
>> > > through my fuel pump.
>> > >
>> > > Those contemplating doing this mod, there is plenty of horizontal
>> > > room for the valve and the Wix filter between the tank and the pump,
>> > > but I might need to research just how important it is to have
>> > > unrestricted flow from the tank to the pump as the valve body opening
>> > > diameter might not be equal to the diamter of the hose, and as the
>> > > upstream filter clogs up, that could I guess cause stress to the
>> > > pump. The van's been getting like 5k a year drive time, so longer
>> > > driving might need more frequent filter changing.
>> > >
>> > > YMMV
>> > >
>> > > DM&FS
>> > >
>> >
>>
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