Date: Sun, 13 Jun 1999 19:35:06 -0700
Reply-To: Coby Smolens <cobys@WELL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Coby Smolens <cobys@WELL.COM>
Subject: Re: hiccuping
In-Reply-To: <199906131501_MC2-793F-215B@compuserve.com>
Content-Type: text/plain; charset="iso-8859-1"
The first thing that comes to mind is "Airflow meter..." - it's the classic
cause of this type of symptom. Our first action (after a visual inspection
of the engine compartment, harness connections, etc.)would be to replace the
AF meter with a known good one for testing. If you can't come up with one,
you can do an electrical test:
Hook up a voltmeter to the output terminal of the AF meter. This is either
terminal 1 or 2 - I always have to hook up the thing to find out - it's one
of the many things I can no longer keep handy in my memory bank. At any
rate, one of the two left hand terminals (viewed from the top with the part
in situ) gives a variable voltage signal back to the ECU after having passed
through the potentiometer. Your mission, should you choose to accept it, is
to figure out which it is and then monitor its signal throughout the range
of its operation.
This voltage variance is due to the position of the sweep arm across the
face of the resistor plate in the meter. Since your engine spends a larger
percentage of its time running at certain RPM (I don't use an "s" after RPM
on purpose - since the acronym is for revolutions per minute it would be
redundant. Sorry - just an anal thing about the language left over from 7th
grade), it's natural that the sweep arm tends to wear out those sections of
the resistor plate first. Anyway, what you're looking for is a "dropout" - a
momentary sag or cutting out in the voltage signal being fed back to the
ECU. I use a DMM with min-max recording capability, as that allows me to
hook the thing up and drive knowing that if there's a glitch it will be
remembered by the machine without my having to watch the whole time. It's
also possible for the glitch to occur faster than a voltmeter can register
it on its gauge. In that case the record feature (which isn't worried about
display) will catch it for later viewing. (These things have become very
inexpensive. I think you can pick one up at Sears or Radio Shack for $20-30.
It's a VERY handy piece of equipment for the owner of a fuel injected
automobile who likes to tinker!)
In other words, once you've got the thing connected, start the engine and
turn the min-max record feature on. Raise the RPM to 2500 and let it fall
back to idle. You should be able to see the voltage rise and fall,
fluctuating between some value greater than zero and some value closer to
12V, as you operate the throttle. Then, if the recorder comes up with a zero
when you check the min and max readings you KNOW the AF meter is bad.
For all that, I still like installing a known good unit for testing. Not as
mad-scientific but very quick and very effective. Good luck!
Coby
Valley Wagonworks
"Intimately acquainted with VW Vans since 1959"
Volkswagen Bus, Vanagon, Westfalia and Eurovan
Repair and Service Specialists
1535 Sir Francis Drake Blvd., San Anselmo, CA 94933
Voice:(415) 457-5628
Fax: (415) 457-0967
http://wagonworks.com
mailto:contact@wagonworks.com
> -----Original Message-----
> From: Woody Halsey [mailto:WoodyHalsey@compuserve.com]
> Sent: Sunday, June 13, 1999 12:01 PM
> To: Coby Smolens
> Subject: Re: hiccuping
>
>
> Dear Coby,
>
> My 83 watercooled Vanagon hiccups at 30 MPH in third and at 50MPH in
> fourth. Given the many times I have come home on the back of a tow truck,
> these incidents, though passing, make me worry. Recently I have had the
> trnasmission replaced and engine rebuilt. Any thoughts?
>
> Thanks.
>
> Woody Halsey
> '64 Beetle
> '89 Diesel Jetta
> '83 Vanagon
>
