NOx problem solved

[John A. Heer]

Hi Gang:

Just thought I would report success in tracking down a NOx emissions
problem.

BACKGROUND:  Purchased 1993 SE-R from Curt Shumaker (AKA "shumax") in
September 2003 and failed Ohio emissions test for NOx by a large margin.
The only relevant mod by Curt was a cat-back exhaust.

DIAGNOSIS:  The flanges between the cat and the cat-back (the Thrush
24-inch resonator) did not seat properly, so there was a small leak
there.  Second, the aftermarket muffler did not allow for enough back
pressure.  As a result, the back-pressure transducer was not triggering
the EGR to function at all.

SOLUTION:  First, we installed 2 thick gaskets and bent the cat and
B-pipe flanges so that they would seat more closely (no leaks).  Next,
we ended up disabling the back-pressure transducer so that the EGR would
function almost perfectly.

The reason that the car never failed emissions before is because, even
though Ohio was testing for NOx data before this year (so it might show
on past emissions reports), Ohio only started failing cars for NOx this
year.  I am curious to see what the readings for NOx were before this
year, just to see if the levels were very different from now.  I doubt
it.  My guess is that the car has been operating without a functional
EGR since the cat-back was installed.

John Heer
93 SE-R not stock
98 SE stock