Date:         Sat, 21 Dec 1996 16:15:13 -0800 (PST)
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         Beth Young <young@sherlock.sims.berkeley.edu>
Subject:      Air Flow Meter/'81 Van/Failed smog


 First, thanks for the replies to my previous post regarding the
 inability to adjust my idle mixture "lean" enough due to an
 apparently faulty air sensor.

 To revisit that thread for a moment: I had broken down and gone to
 VWofA to get my idle mixture adjusted.  Tech said that although he
 had adjusted mixture screw all the way out, he couldn't get CO down
 low enough and said that the air vane wasn't moving enough in
 response to changes in air "push" caused by changes in position of
 the screw.  I was frankly dubious about this explanation since it
 seem to me that adjustment of the screw acted as a pure bypass,
 allowing more or less unmetered air into the engine.  All respondents
 to my question about this agreed.

 Guess what?  He's right!  I popped the cover of my air sensor and,
 with the engine running, adjusted the screw all the way in and all
 the way out.  The air vane (as indicated by the "sweep" arm I could
 see) definitely moved in response to my adjustments!  I guess just
 because the shop coveralls say "VWofA" doesn't mean that everything
 they say is wrong!  (It doesn't make it all right, either.)

 Anyway, I found Dan Houg's post in the archives about adjusting the
 air meter.  After a personal reply from Dan regarding a question I
 had (Thank you, Dan) I went out this morning and started adjusting.
 Monitoring my progress with my ohm meter attached to the O2 sensor, I
 got volts fluctuating just around .5, exactly as specified!!
 The engine was definitely running better, so I hopped into the car to
 get it smogged.

 And it failed again!!  As before, idle CO was OK, idle HC was a bit
 too high.  This tech said that I had a leak in my exhaust (O2 reading
 was around 11% - isn't this kind of low?) and told me to get it
 fixed.

 Now, I put this engine in about 1,500 miles ago, used all new
 gaskets, torqued bolts properly, etc. and I don't think I have an
 exhaust leak EXCEPT FOR WHERE THE MUFFLER MEETS THE X-OVER PIPE (this
 is a California van).  But as I understand the theory behind exhaust
 leaks and rich running, the problem is that the O2 sensor gets fooled
 by the excess oxygen, and richens the fuel mixture.  Since the leak
 is downstream of the O2 sensor, I wouldn't think this would matter.

 Questions:

      1) is 11% O2 out the pipe really too high?

      2) will an exhaust leak such as I described, i.e., downstream of
         the O2 meter, give false readings?

 Thanks everyone.

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Tom Young               young@sherlock.SIMS.Berkeley.EDU
Lafayette, CA  94549    '81 Vanagon
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