Date:         Fri, 11 May 2007 05:27:58 -0600
Reply-To:     Martin Jagersand <jag@CS.UALBERTA.CA>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Martin Jagersand <jag@CS.UALBERTA.CA>
Subject:      Solved thanks to list! Re: Jerks/surges when going from coasting
              to acceleration
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

A few days ago I took a third (or was it fourth) look into the
ECU-engine wiring. Indeed, as many on the list (Mark, Kenneth,
Alistar, Dennis...) had suggested, the problem with jerking on
acceleration was an incorrect throttle position signal to the ECU.

At some point someone had swapped two plugs on the wiring,
even adjusted lengths on the cables a bit, and put it back so it
"looked right", but didn't work right. Dennis description below
explains precisely what happens.

The bus had two brief owners before I bought it. I can't help
thinking that they probably brought it with the problem, never got
it fixed and eventually gave up and sold.

With a bit of tactile exploration I pulled out fried wiring from under the
throttle body, where the throttle posisiton switch sits. Right now
I just left the throttle position ECU wire unconnected. Seems to
run just fine this way. Maybe acceleration is a bit slower? I didn't
notice much difference though.

If I get more time I will try to pull the throttle body and get to the
switch
on the underside. Looks like the throttle body is mounted with two phillips
screws. I hope I can get it out without removing too many other parts.
My travel toolkit is a bit limited, and I don't have sockets to fit the
cramped
area.

Martin
- -
Martin Jagersand
University of Alberta
http://www.cs.ualberta.ca/~jag/
On 4/23/07, Dennis <d23haynes57@hotmail.com> wrote:
>
> 12 volts does not go to the throttle switch. That goes to the auxiliary
> air regulator. Since you had the 12 volt connector to the throttle switch,
> it is fried. Now, since the 12 volt connecter is going to the switch, I'll
> assume the other connecter is going to the auxiliary air regulator. Since
> the regulator is just heating coil, the ECU is seeing this as a switch
> that is always closed. Closed at full and open throttle is the
> expectation. So when you accelerate, the ECU thinks the throttle is closed
> so at ~1,300 rpm you go into fuel cut off (Decel) while trying to
> accelerate. Makes for a great ride. Then at some point you go into fooling
> the ECU into en richened full throttle acceleration. Yes, it is confused.
> Swap the connectors and replace the switch.
>
> Dennis
>
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
> Martin Jagersand
> Sent: Monday, April 23, 2007 1:31 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: Jerks/surges when going from coasting to acceleration
>
> Hi,
>
> It's a gas, fuel injected engine. It's actually a re-import to Germany
> from
> the US.
> I suspect it's a 1985, but could be '86 model. (German records show
> re-import date,
> not real year) VIN is WV2ZB0258FH068651
>
> I finally identified the right connector for the throttle body switch.
> Turns out I have the "combined switch" arrangement found in Bentley
> on p. 24.35 and 24.58. (I had previoulsy been confused and probably
> pulled the wrong connector when I didn't find the two usual switches on
> top of the throttle body)
>
> Checked switch:
> Switch always open.
> Checked other end of connector: always 12V.
> I used a high impedance DMM, so not sure what voltage would be
> with an analog meter.
>
> Bentley says voltage should be 5V. So I guess there is a risk that this
> IO port on the computer is broken.
>
> I had thought to try the "cut off test" by shorting the connector,
> but then was afraid I might break something more.
>
> More precisely the jerking/surging symptom that started the investigation
> manifests itself as:
> 1. when slowly poressing the accelerator from idle for a little while
> nothing
> happens, then it surges.
> 2. When coasting with little engine power the bus can get into some kind
> of oscillation behaviour. It surges forward, then retards, surges etc.
>
> Martin
>
> On 4/22/07, Kenneth Lewis <kdlewis@northstate.net> wrote:
> >
> > You weren't quite clear, is it a diesel you are having problems with? If
> > not
> > I would tackle the three throttle body adjustments. Especially the idle
> > position sensor.
> > Ken Lewis
> > http://neksiwel.20m.com/
> > Vanagon mods, tech info and O2 sensor help
> >
> >
>
>
> --
> Martin Jagersand
> University of Alberta
> http://www.cs.ualberta.ca/~jag/
>
>


--
Martin Jagersand
University of Alberta
http://www.cs.ualberta.ca/~jag/