Date:         Mon, 22 Oct 2007 11:04:12 -0400
Reply-To:     "Eastman, Cecil @ ELM" <Eastman.C@ATWOODMOBILE.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "Eastman, Cecil @ ELM" <Eastman.C@ATWOODMOBILE.COM>
Subject:      Throttle Valve Switch - Lesson Learned
Content-Type: text/plain

For folks who haven't traipsed this path, allow me to guide you a little.

I've been having problems with fuel flow/injection/etc.  For starters, the
Throttle Valve Switch on my late '85 was dysfunctional on account of it
being missing.  Some DPO decided they could live without it, I guess.  So,
without having an example present to use as a model, I had to figure out
what in blazes the Bentley was trying to tell me.

Beginning in late '85, the Digijet TVS is one unit that sits under the
throttle body, upside down.  (Prior to mid-'85, there were two separate
units that performed the same functions.)  There is a metal spring that
works like a telegraph key.  When the key is depressed, opens a circuit and
tells the ECU to minimize the fuel supply when you take your foot off the
gas.  You can hear it click when it activates.  Without this gizmo, you get
the bucking sensation as the engine is alternately starved and fed gas.  You
get the same problem if the TVS isn't adjusted properly.  The keys: the
position of the TVS relative to the cam on the under-side of the throttle
body, and the shape of the metal key.

Positioning:  the TVS must be positioned so that the switch is activated
when your foot is off the gas.  Technically, it should activate within .002"
- .004" from complete throttle close, but I found that to be such a tight
tolerance that it didn't make much sense because your foot can't control the
gas pedal that closely.  To position, loosen the left clamping bolt, then
turn the right bolt, which is an off-center cam.  Caution: the allen head of
the cam on my bus was pretty weak and I managed to easily strip out the hex.
The only way I can adjust it now is to fiddle with it manually.  Using a
multi-meter, the reading should be zero ohms when the throttle is closed.
Using your ears, you should hear a click as the switch is engaged when the
throttle is completely shut.  This brings us to step 2.

Metal Key:  I found that my TVS wasn't activating at any setting because the
key was set too short.  It wasn't even contacting the cam at any position.
So I bent the key into a taller shape so that it would depress enough to
activate the switch when in contact with the cam.  Then I re-positioned the
TVS so that the activation came at the right moment, and voila, done deal.

Hope this helps someone.

Cecil
'85 Westy Wolfsburg "Der BrotKasten"