Failed Then Passed Smog
 

Hello all, thought I should make a post that might help someone else having similar smog test issues (California smog specifically in my case). Backstory on the car, it has been sitting since 2015 or 2016 after overheating issues. Found a crack in the cylinder head which was finally replaced a couple months ago. Smog failed twice because of high NO numbers, then passed on the 3rd try.


Here’s the breakdown on each test attempt:


1st Test:
After being repaired the car was only driven around the block a couple of times, still had the old fuel in it. It was driven straight to the smog test station about 5 miles away:

15 MPH:
HC (PPM):
MAX: 59
MEAS: 48
CO (%):
MAX: 0.34
MEAS: 0.14
NO (PPM):
MAX: 486
MEAS: 775

25 MPH:
HC (PPM):
MAX: 35
MEAS: 12
CO (%):
MAX: 0.33
MEAS: 0.01
NO (PPM):
MAX: 502
MEAS: 673


2nd Test a week later:
Drove until the gas was down to near empty
Put in a bottle of Techron (non concentrate), plus 6 gallons of 91 Chevron
Drove around 30 miles before going to the test station
Car sat for around 10 minutes before test

15 MPH:
HC (PPM):
MAX: 59
MEAS: 13
CO (%):
MAX: 0.34
MEAS: 0.04
NO (PPM):
MAX: 486
MEAS: 565

25 MPH:
HC (PPM):
MAX: 35
MEAS: 4
CO (%):
MAX: 0.33
MEAS: 0.01
NO (PPM):
MAX: 502
MEAS: 694


3rd Test a week later:
Changed some parts:
Oxygen sensor (Bosch 13231)
Fuel filter (Mahle KL66)
Spark plugs (NGK 3199, replaced new NGK 7092 plugs that were installed when the cylinder head was replaced)

Drove until the gas was down to about 1/4
Put in 1/2 bottle of Red Line SI-1, plus 6 gallons of 89 chevron
Drove around 20 miles

The next day, day of the test:
Cleaned the MAF with CRC MAF cleaner
Drove around 60 miles before going to the test station
Car sat about 5-10 minutes before test

15 MPH:
HC (PPM):
MAX: 59
MEAS: 39
CO (%):
MAX: 0.34
MEAS: 0.08
NO (PPM):
MAX: 486
MEAS: 130

25 MPH:
HC (PPM):
MAX: 35
MEAS: 15
CO (%):
MAX: 0.33
MEAS: 0.05
NO (PPM):
MAX: 502
MEAS: 27


So the NO numbers changed really drastically. I wish I knew for sure which one of the changes was the main one responsible for the fix, the smog shop said it was likely the O2 sensor. Or was it just the old gas finally getting out of the system? It was having an intermittent 1286 code for Knock Sensor Test Pulse that eventually went away after putting in the first batch of fresh gas.

Hope this is helpful for someone else. I was going to replace the cat next, and was actually looking them up while in the waiting area during the 3rd test lol.

Thanks for the detailed write up. How many miles on the car? I've had similar problems. New o2 sensor helped me in 2019, but almost didn't pass in 2021.

Got 183K miles on it. Now trying to fix up an oil leak and also a power steering leak. It don't stop :biggrin: