Join the community and post your question. Use our Ask-A-Tech for free now! ASE experts standing by.

Forum > General Smog Check > Question

Toyota Corolla High Mileage Failed NOx

I own a 1994 Toyota Corolla DX that has 292000 miles on it. I tried to smog check my car and it failed the smog check. The mechanic then checked the EGR system and replaced the EGR valve. He smog tested it again and it passed everything accept the 15 mph per hour part of the emission test and was still a gross polluter at 15 mph. It passed the 25 mph portion. Can it be my Toyota Corolla catalytic convertor that is bad? Is that why it's a gross polluter?

Answer:

Before condemning your Toyota Corolla's catalytic converter we'd recommend checking two things closely. One is engine cylinder compression, and the second is air/fuel ratio. Your Toyota has quite a few miles on it and over the years probably built up a good amount of carbon on the piston and valve heads. Carbon build up leads to high cylinder compression and high cylinder compression leads to high engine temperatures. Since NO is created when engine temperature rise above 2500f, on vehicles with high mileage, carbon build up and high cylinder compression should not be ignored when diagnosing NOx problems. The second thing to make sure is not causing your Toyota Corolla to produce high NO is a lean fuel mixture. A lean fuel mixture is when the engine receives less fuel then is necessary to obtain efficient combustion. Lean fuel mixtures may be due to vacuum leaks or defective fuel metering components. Vacuum leaks will allow the suction of additional and un-metered air into the combustion mixture or exhaust (depending on where the vacuum leak is located) disturbing pre/post fuel combustion and increasing NOx emissions. We recommend replacing the catalytic converter only after all other emission systems have been diagnosed and no faults found. posted by SmogTips Support

Related questions and answers you might find useful:

How Do I Get a Smog Check Waiver? by Margaret

Do I Need a Smog Check This Year? by Joy

Mini Cooper DMV Registration Due in 5 Day Won't Pass Smog by anne

2001 Jeep Grand Cherokee Laredo with K&N Air Filter by David

1995 BMW M3 Gross Polluter High HC & NO @ 15MPH by Jared

View SmogTips.com in: Desktop / Mobile