Date: Sun, 10 Mar 2013 10:18:51 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: Throttle stop switch? Stumbles on resume throttle..
In-Reply-To: <CAHTkEuLF2dtr9TyG=KEd=pEqTb6Ds7w+wrtU9Qfudh4NypLA4A@mail.gmail.com>
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The same switch contacts are used for both closed and open throttle with the
combination of RPM and AFM position being used to tell the difference. The
switch should be closed (0 ohms) at full or closed throttle. It needs to
open fairly quickly when the throttle is opened. Some of the behavior you
noticed is normal. When the throttle is closed and the engine is being
overrun the fuel injectors actually turn off. The causes a number of things
to happen including the cylinders going cold during extended closed throttle
operation. Now for the tricky part. As the throttle is opened or the overrun
goes away and the injectors resume operation the O2 sensor is ignored for
some time. This is where correct baseline settings are so important. If the
mixture is off and the system relying on O2 sensor trim all the time there
will be an additional delay before things work right. Of course if traveling
and changing altitudes the correct mixture at sea level will not be the same
at 8,000 feet so O2 sensor trim will be used much more. Also keep in mind
that at 8,000 feet your engine has lost 24% of its available horsepower
Dennis
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-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Don Hanson
Sent: Sunday, March 10, 2013 9:44 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Throttle stop switch? Stumbles on resume throttle..
I have a Digifant ignition on a 93 Jetta inline gas powered van.. When
I coast down a long grade at higher RPMs (highway speeds) there is often a
slight hesitation as I resume pushing on the gas pedal...This hesitation can
be more pronounced at high altitude, I think. Recently, at over 8000'
elevation I felt an almost "engine off" delay of perhaps a full second when
I reached the bottom of a slope and put my foot back on the pedal. If I
keep a very slight amount of throttle open, there is no hesitation.
Another diagnostic symptom (could be exacerbated by a small crack in my
exhaust downpipe) is that rarely, my exhaust will "Pop!" loudly a single
time when I drop throttle at lower rpms. This 'delayed throttle response'
was particularly un-nerving as I was descending a very slick and windy
snow-covered pass recently..."exciting moments" as the engine resumed drive
after descending slowly in a lower gear...
I have a switch that looks somewhat thin and flat, with a
leaf-spring/bent lever looking prong that is activated by a small post in
the linkage near my throttle body. I assume that is the throttle stop
switch. It seems to activate (mechanically) properly...it "click" when
you just crack the throttle and 're-clicks' when you release the throttle...
I can't decipher my 2 Bentlys (Vanagon and Cabriolet) well enough to even
figure out which switch I have and how to go about testing it. There
seems to be a couple of very different ones used on various Digifant
systems. Can someone guide me as to how to test this part? Does anyone
have any other ideas as to what might be causing this somewhat troublesome
delayed throttle response?
Don Hanson
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