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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