[s-cars] my '92 failed smog

[Theodore Chen]

i replaced the O2 sensor with a generic bosch sensor in january 2006, about 30k miles ago.  could the replacement have failed already?  the check engine light isn't on and i haven't seen it go on, but i'll check the codes.

the HC at idle is 211, and at 2500 rpm it's 68.  if it's an ignition problem, wouldn't the HC be higher at 2500 rpm?  also, the engine seems to be running smoothly.

after getting home from work, i left the engine running and checked the exhaust manifold with an infrared pyrometer that has a laser sight.  i took multiple readings of each cylinder runner, about an inch from the head (a bit tricky to do because there's not a lot of space).  all of them read in the 500+ degree range (#3 was the hottest at 570 degrees), except for the #1 cylinder at the front of the engine, which read 460 degrees.  i don't know if this is normal.  any ideas?

vacuum leak is possible, but the oxygen levels are very low.  a vacuum leak would create a lean misfire, and i would expect to see a lot of excess oxygen.  right?

-teddy

----- Original Message ----
From: Kent McLean <kentmclean at comcast.net>
To: s-car-list at audifans.com
Sent: Wednesday, April 9, 2008 4:03:22 AM
Subject: Re: [s-cars] my '92 failed smog

Theodore Chen wrote:
> here are the numbers:
> idle (792 rpm) CO2 14.3% O2 0.70%, HC 211ppm (max 120) CO 0.11% (max 1.00)
> 2512 rpm CO2 14.4% O2 0.40% HC 68ppm (max 140) CO 0.32% (max 1.00)

Googling: emissions "high hc"
yields these links:

http://www.nichols.nu/tip517.htm
http://en.allexperts.com/q/Toyota-Repair-832/Failed-Calif-Emissions-HC.htm
http://autotechrepair.suite101.com/article.cfm/a_question_about_a_question

They seem to agree on incomplete combustion due to a misfire, and to
check everything in the ignition system - plugs, wires, etc., including
the O2 sensor. My Audi specific guess would be a POS starting to fail.

Another point they make is a too-lean mixture caused by a vacuum leak,
so check all your hoses.

Pulling the DTC codes wouldn't hurt, either.

-- 
Kent McLean
'99 A4 Avant, w/ quattro, V6, Tiptronic, :)
'91 200 TQA #1, backup car
gone but not forgotten:
'94 100 S Avant, "Moody", now with new owner
'91 200 TQA #2, up in smoke 2
'89 200 TQ, "Bad Puppy", up in smoke
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