My 1999 Acura Integra LS with 144k (well maintained) but failed smog twice!.
Car runs perfect and no CEL either. Car was warmed up well.
The upstream O2 sensor was replaced in 2016 - preventive maintenance. See table below for historical NO values:
In 2019 it failed too - just needed new air filter! But I also used CataClean - then NO went up to 646 at 25mph from previous high of 78! Something happened due to CataClean?
When an AC issue happened (IAC valve needed a clean), the shop adjusted the throttle to give more gas - later it was reversed but might not have been to the correct level - I didn’t think it was a big deal since there is a slack on the metal cable - Is the engine still getting more gas at idle causing high NO at 15mph?
Oh, for the re-test I followed Scotty's advice by adding 1 gal of Liquor thinner. I ran the car for 30mins at 2500rpm. Car runs better now and passed at 25mph but failed at 15! I still has about 8 gal of mixed gas in the tank.
It seems your Cat has lack of efficiency. Try this: Use higher octane gas. If the issue stil exists, try to clean the Cat by removing it and put it in dishwasher soap. Scotty has a video on this.
Btw, have you cleaned the MAF sensor? I would also check the sensor function.
Thank you @yaser
My car has a MAP sensor - ie manifold absolute pressure sensor
It was never cleaned. It might be hard to reach - unsure
I got some live stream data while the car was running:
At 2k rpm:
- O2 sensor output voltage-B1S2 = 0.095 - Low?
- O2 sensor output voltage-B1S1 = 0.210 (replaced in 2016)
- Ignition timing advance for #1 cylinder= 33.5 BTDC - high?
At 800 rpm:
- O2 sensor output voltage-B1S2 = 0.015 - Low?
- O2 sensor output voltage-B1S1 = 0.115 (replaced in 2016)
- Ignition timing advance for #1 cylinder= 15 BTDC
manifold absolute pressure sensor = 4.64
Anything obvious?
When I drive, the downstream O2 sensor fluctuate between 0.02 - 0.88 volts!
What should be the Fuel Trim mixture?
Short Term Fuel Trim - Bank1 = 14.8 - 7.0%
Short Term Fuel Trim B1S1 = 12.5- 4.7%
Short Term Fuel Trim B1S2 = 7.8 - 11.7%
Long Term Fuel Trim - Bank1 = 5.47%
I checked for O2 sensor functionality at lean condition.
I disconnected the PCV and O2 voltage stopped fluctuating and fell below 0.1 volt - I didn’t bother checking for Rich condition given its NTK part that was replaced in 2016
< https://dannysengineportal.com/o2-oxygen-sensor-function-failure-symptoms-testing/>
Also cleaned the MAP sensor.
I found a bad PCV valve - its only 2 yrs old!