After having passed the California smog check for 2 tests (4 years) in a
row, my stock '94 Del Sol ("S" model with 1.5L engine) failed today. :-(
It's the first time I've ever had any car fail the Smog Check, in 20 years
of living in California.

I have never made any modifications to the engine, and I take it in for
regular maintenance according to the maintenance schedule. It has been
about 6500 miles since its last oil change, and I don't use any pour-in fuel
additives. It is running normally with no noticeable engine problems.

Here in California the DMV has recently made the Smog Check test more
sophisticated, using a 'dynamometer' (treadmill) to test the car under load.
They test the car at a simulated 15mph and at 25mph. They also added a NOX
(nitrous oxide) emissions check, and that's the one that my car failed, but
only at 15mph.

As for my other emissions test results, my Del Sol had extremely low CO2,
O2, HC and CO emissions at both 15mph and 25mph, but failed the Nitrous
Oxide (NOX) test at 15mph. In fact, the NOX emission was about 3 times
higher at 15mph than at 25mph, which seems counter-intuitive. I had driven
the car at least 15 miles before arriving at the test facility, so it was
well warmed-up.

Has anyone else seen this kind of failure with an older Honda Civic or Del
Sol? If so, what was the culprit? I'm trying to get an idea how much it's
going to cost to have it fixed.

Thanks for any ideas, feedback, or sympathy. :-)

-DK