Failed emissions, high HC and NOx.

[GTOger]

QUESTION IS UP-FRONT. Read the story if you'd like to weigh in!

Q: Dear readers, I'm wondering if I need new catalytic converters.

1990 ZR-1 with just over 38,000 miles.

Back in December, I took the car for the routine Texas emissions test, my 3rd since owning the car. For the first time ever, it failed. The HC and NOx were way out of whack.

Readings from 12/21/2012
HC High-speed standard: 148 ppm
HC High-speed tested: 209 ppm

HC Low-speed standard: 152 ppm
HC Low-speed tested: 229 ppm

NOx High-speed standard: 1047 ppm
NOx High-speed tested: 1915 ppm

NOx Low-speed standard: 1149 ppm
NOx Low-speed tested: 2064 ppm

I went back the next day after giving the car a thorough flogging, blowing it out on the highway, and making sure she was good and warm for the test. The result: hydrocarbons were worse, NOx was better, still failed.

HC High-speed standard: 148 ppm
HC High-speed tested: 212 ppm

HC Low-speed standard: 152 ppm
HC Low-speed tested: 244 ppm

NOx High-speed standard: 1047
NOx High-speed tested: 1503 ppm

NOx Low-speed standard: 1149
NOx Low-speed tested: 1793 ppm


The car sat for a couple weeks before we could make a trip to go see Corey at Henderson Performance Technology. Corey thought perhaps the car was running lean. As it turned out, it was a bit fuel-starved and needed a new fuel pump and strainer. Low fuel pressure = bad fuel atomization = bad burn and spitting unburned gas through the exhaust.

After the new fuel pump, the car felt a bit (not a ton) more responsive and wasn't smoking anymore (it had been collecting some black soot on the passenger-side bumper). Unfortunately, since Henderson Performance is not in an "attainment area" (which means they don't have to get emissions inspections there) we did not have a way to check for improvements. The recommendation was take it home, flog it a bit, get re-tested. If it failed, run some "Guaranteed To Pass" through it and try again.

So I did. Took it home, flogged, re-tested. FAIL.

Ran by to pick up a bottle of G2P (guaranteed to help you pass your emissions test or double your money back!). Followed all the instructions (added to a fresh tank of super unleaded, ran the entire tank, filled with fresh gas and re-tested). Went for another test. FAIL.

We're getting closer, but not close enough.

HC High-speed standard: 148 ppm
HC High-speed tested: 206 ppm

HC Low-speed standard: 152 ppm
HC Low-speed tested: 257 ppm

NOx High-speed standard: 1047 ppm
NOx High-speed tested: 892 ppm

NOx Low-speed standard: 1149 ppm
NOx Low-speed tested: 1420 ppm


Based on my poor memory of a discussion I had with Corey, as well as some other reading that I have done around the Interwebtubes, when we have high HC and high NOx that is a good indicator of a lean mixture or bad cats.

My working theory at this point is since we absolutely did have a fuel mixture problem, and we were likely spitting unburned gas into the exhaust, we've destroyed the cats.

But I'm just a dumb guy with a car. I'd love to hear either some confirmation or some other suggestions.