Date: Mon, 21 Nov 94 13:23:09 EST
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: dcarment@ccs.carleton.ca (David Carment)
Subject: Re: Oxygen Sensor / Full Throttle Switch
Lee Wood writes:
>
> I replaced by O2 sensor on my '81 Westphalia last week and used the
> generic replacement part from my FLAPS (Auto Parts Club). It was
> *not quite* identical to the original; different numbers and
> markings of course, slightly fewer slits and heavier gauge metal on
> the part that inserts into the exhaust manifold, but other wise the
> same. The wire (single-wire installation) came with a crimp-on
> connector already installed. All I had to do was cut the old wire,
> strip the end, insert it into the new connector and crimp it.
> Voila! It runs fine. No real performance (term used loosely)
> gains; I guess my fuel mileage will tell if there will be any
> improvement. The best part was that the generic sensor cost about
> $26!
>
> Of course getting the old one out was another story! (details on
> request, but the procedure involved a hammer and some cursing)
>
> New topic...
>
> Yesterday I was out playing in the engine compartment with my
> multimeter and 12V test light and following the fuel injection
> troubleshooting instructions in Haynes. No real problems, just idle
> hands. ;p When I tested the full-throttle switch on top of the
> airflow sensor/throttle plate assembly, I couldn't get any results.
> The ignition switch was on. Haynes said to connect the test light
> between the _uninsulated_ lead to the switch and ground, but both
> leads were insulated. So I tested both ways: the light never came
> on. I can hear the switch click, but nothing happens. Then I
> tested the two leads connected to the switch (both white and the
> same gauge) with the ignition switch on. No power in either of
> them. All fuses are intact. I can't decipher the Haynes wiring
> diagrams (sure, like I could decipher _anybody's_).
>
> My questions:
>
> 1. Am I missing something here? Should one of the two white wire
> leads to/from the switch be hot with the ignition switch on? Which
> one, the front or rear (numbered 52 and 3, if I remember correctly)?
> If so, are there any obvious places I should check for a short or
> break? Is now the time to break down and purchase a Bently manual?
>
> 2. What does the full throttle switch _do_? Do I need to fix it?
> What's the worst that will happen if I don't?
>
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> To: VANAGON@LENTI.MED.UMN.EDU
>
Hey Lee, glad to see SOMEONE thinks along the same as me. I too recently
replaced the O2 sensor on our 82 and found no major gains on fuel economy
fron; but did find that the idle is much steadier and low.
On testing the full throttle switch. This stymied me as well when the
engine was being broken in, since I assumed that the lack of high end power
was due to an ineffective throttle switch.Here is what I did:
Tested the switch as per Hayne's - and like you found the instructions
wanting or unclear-essentially I could not get the test light to go on with
the ignition on and assumed a faulty switch;
Tested the switch off the the intake and it worked fine- hmm switch seems ok;
(this is easily done with a light, leads and the car battery);
Tested the continunity of the leads running to the switch from the left
hand side "black box" and the computer brain. All leads showed continuity;
Was left with the possibility after having removed all other causes that
the black box (between FI switch and igniter) was faulty - replaced black
box at (90 US!). No effect on throttle nor getting the light to go on
during testing hmmm.
Finally when the vehicle was in for emmissons tests, was told by reputable
VW mechanic that the full throttle setup is marginal at best. He said you
could remove the device and would not notice the difference. I tend to
agree with him, at full throttle the difference is negligible; and yes the
switch is properly adjusted to the cam.
Conclusion - still unclear what the full throttle switch is intended to do
: advance the curve, richen the mixture or a combination; believe that is
not crucial but nevertheless a problem.
One solution - glancing through Bentley's at the bookstore; they have
a detailed description of adjusting and testing the full throttle switch
and black box - this would be my next step....
Perhaps some one out there can throw some light on the issue (PhD's not
required).....DC
--
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David Carment
School of International Affairs
Carleton University
Ottawa, Ontario
K1S 5B6
voice - (613) 788-2600-6662
fax - (613) 788-2889
Email address: dcarment@ccs.carleton.ca
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