Date: Mon, 29 Sep 2003 18:45:51 -0600
Reply-To: tom ring <taring@TARING.ORG>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: tom ring <taring@TARING.ORG>
Organization: Tippen Ringware
Subject: Re: The "Other" Vanagon Syndrome, Part II
In-Reply-To: <BB9DC94A.81E5%tornadored@earthlink.net>
Content-type: text/plain; charset=US-ASCII
I am less experienced than many on the list when it comes to the AFM, but I am
experienced in electronic parts wearing out in general.
The AFM doesn't have anything magical in it as far as I can tell. It is a
fairly interesting version of a variable resistor, commonly called a
potentiometer or "pot", with an airflow measuring door and a spring with an
adjustable preload. Add the temp sensor to the mix and that's it.
The pot is probably the only thing that wears significantly in any of them. It
has two connection points on the pickup, which presumably the designers did to
make it more reliable. It probably doesn't, as both points will wear at the
same rates.
The problem with all these pot based systems is that we tend to run the engine
at just a few airflow rates for most of our driving, which causes most of the
wear to occur at just a few fairly narrow points on the range of pot. For the
type of driving vanagons drivers do, mostly at one or two speed points, I'd
bet.
When visually inspected, the pot may look good, but can really have very small
dropout points within the most used areas. I think, personal guess here, that
one thing the capacitor fix does is allow the AFM to hit a bad spot, have the
engine start to drop rpm a bit, and hit a good spot, then maybe overshoot a
bit, without a huge change in the voltage fed to the control unit. Which
allows it to recover, and do the cycle again. The illusion of a good AFM, when
in fact it has a small problem. From the few measurements I've made on my 2
old and 1 new AFMs, this may be the case.
Just my guesses.
tom
On 29 Sep 2003 at 11:34, James V wrote:
> Coincidentally... I just returned from a trip to Yellowstone (from so cal)
> as well, and had a similar experience.
>
> On the way there, the van ran fine for the first 300 mi. Then, north of
> Vegas the bucking began. Slowly progressing until it died on the highway.
> Turning it off, then on would cure it for a time. Having left my brand new
> spare AFM at home (!), I had similar thoughts of bad gas and such and dumped
> a bottle of fuel cleaner in and poked the engine at the next gas station.
> No dice, of course.
>
> Got to Yellowstone and drove all over the park - a few hundred miles - No
> problems at all. I thought the problem was somehow fixed, and was expecting
> a leisure ride home.
>
> But just towards the end of the first day of the return trip (500 mi), the
> problem returned. The thing that I noticed and from what I've read, the
> problem manifests after a long period of cruising, (I'd usually have the
> cruise control on).
>
> So, on the second day of the return trip, I varied my speed, usually between
> 65 and 75 the entire way home. I'd still use the cruise, but I'd cancel it
> every 15 min or so and change speed and/or let off the gas completely and/or
> de-clutch to drop the revs for a couple of seconds. I didn't experience the
> problem at all that day - 500 mi of straight highway driving. Now that I'm
> back home to city/fwy driving, it's been fine.
>
> I'm fairly certain my problem is AFM related - I don't have the capacitor
> fix. Which brings me to my questions:
>
> Is the vanagon syndrome caused by a non-capacitor-fixed AFM or simply a bad
> AFM, or either, or both? Had I swapped out my AFM for the new one, would I
> be just as likely to experience the problem, since it wasn't "fixed"? And
> what exactly is happening that makes the AFM go nutty???!
>
> Thanks,
>
> James
> 90 Carat
>
>
> On 9/28/03 16:48, "Harald Rust" <harald_nancy_vw@YAHOO.COM> wrote:
>
> > From http://autos.groups.yahoo.com/group/vw-camping/
> > After spending many days touring the Yellowstone
> > geysers, wildlife viewing, photographing the Grand
> > Tetons, and driving hundreds of miles in the parks at
> > 8,000 feet, it's time to go back home to Washington.
> > In the parks, the vanagon runs perfect, and
> > our confidence has returned.
> > We exit Yellowstone at the north entrance, and
> > proceed on to Livingston, Montana, and there top
> > off with Exxon premium and get back on I-90 west.
> > After 50 miles on the highway, it starts all over
> > again, bucking, backfiring, loss of power, as
> > if someone back in the engine compartment cut
> > the fuel supply off.
> > We are 800 miles from home, and there are some big
> > mountain passes in front of us, and it's
> > becoming very nerve-wracking.
> > We pull over once again, move all the things onto
> > the camper floor, and open up the engine compartment.
> > Start up the waterboxer, and now it confounds us
> > by idling really nicely again.
> > Back on the freeway, after another 60 miles or so,
> > it starts stumbling again. After a very long day
> > of slow driving, we limp into Butte, Montana
> > with 35 mph and the emergency flashers blinking.
> > Camp at the KOA. In the morning we buy a new fuel
> > filter at a store, and replace the old one
> > at the KOA.
> > (for good measure, also put in the spare coil.)
> > I cut open the old fuel filter, which
> > is also fairly new. Hardly any dirt in it.
> > The paper element looks just fine.
> > There are a few water droplets in the fuel,
> > but nothing that should make the vanagon stop running.
> > People blame a lot of problems on bad gas.
> > I was always skeptical of that, because the other
> > cars seem to run ok on the same gas.
> > The vanagon isn't that different, or is it?
> > So if it's not bad gas, what is it then?
> > The symptoms are always a leaning out of the fuel.
> > So finally we realize it could be clogged fuel
> > injectors. Maybe clogged or worn fuel injectors
> > are more sensitive to reformulated gas containing
> > ethanol(?)
> > Maybe that's the reason some vanagons seem to
> > run better on certain brands of gas.
> > In Western Washington our vanagon always
> > ran great on the cheapest regular gas.
> > Maybe the heat of all-day freeway driving makes the
> > varnish deposits in the fuel injectors stick(?)
> > Stuck fuel injectors is something that we hadn't
> > thought of up until that point.
> > Our injectors have been replaced once, but are
> > about 9 years old with 110,000 miles on them.
> > Never really added much detergent to clean them
> > on a regular basis.
> > So we drive down to the gas station mart, and
> > stock up on 5 bottles of Techron additive.
> > The guy behind the counter comments on how
> > expensive the stuff is, and that's why he rides
> > a bicycle.
> > So we start by pouring 2 bottles of Techron in
> > the fuel tank. Get back on the freeway, a little
> > later the vanagon starts bucking once again.
> > Another 100 miles later, the bucking becomes
> > less severe, and sometimes I'm even able to
> > keep up with traffic on a uphill grade.
> > At the next fill up, add more Techron.
> > By the time we reach Idaho, the vanagon runs
> > really great again, and the stumbling totally
> > disappears. We drive all the way back home
> > without any problems.
> > Still with all this, we don't consider the
> > problem fixed. It's probably time to replace
> > the fuel injectors, or at least, take them out,
> > and send them in for ultrasound cleaning or something.
> > Some research shows that European car fuel injectors
> > are more sensitive to sticking than domestic.
> > So it looks like we'll be replacing the fuel
> > injectors soon, even though the vanagon is
> > running really well again right now.
> > Harald
> > '90 westy
> >
> >
> > __________________________________
> > Do you Yahoo!?
> > The New Yahoo! Shopping - with improved product search
> > http://shopping.yahoo.com
>
------
Tom Ring K0TAR, ex-WA2PHW EN34hx
85 Westphalia GL Albert
96 Jetta GL The Intimidator
taring@taring.org
"It is better to go into a turn slow, and come out fast, than to go into a turn fast
and come out dead." Stirling Moss
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