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

Forum > Failed Smog Test > Question

BMW 318is Failed Smog Test for High HC and NO

I have a 1997 BMW 318is and it failed the smog inspection with high HC and High NO, at low speed.

Here are the results at 15 mph: RPM: 2070 %CO2: 14.7 %O2: 0.8 HC: 116 CO: 0.22 NO: 1255 Max HC is 60, and max NO is 459. So my BMW failed the HC and NOx.

The results at 25 mph were well under max allowance: RPM: 2192 %CO2: 15.0 %O2: 0.4 HC: 28 CO: 0.03 NO: 245

Do you have any ideas why I would fail both HC and NO, and both only at low speed? Where should I start checking and how? Thank you.

Answer:

Your BMW 318is is a non-EGR valve equipped vehicle. NO reduction is primarily controlled by proper air/fuel mixture and the catalytic converter. Once all other emissions components are inspected, and either fixed or found to be functioning properly, we may suspect a damaged CAT (Catalytic Converter)… possibly plugged up. Your BMS 318's CAT may have become plugged up if it has suffered a substrate breakdown. This may have happened due high exhaust temperatures and a rich fuel mixture. After first inspecting the fuel and ignition systems, an intrusive CAT test and Back Pressure/Vacuum test may be performed. These tests will determine whether the CAT is operational. The important thing to remember is if in fact the CAT is damaged, you have to ensure a pre-existing problem is not the culprit. You do not want to install a new CAT only to damage it after a few months. As mentioned a CAT melt down usually occurs due to high CO (Rich Fuel), old age, and extreme heat. It is recommend to suspect your BMW's CAT is damaged only after a complete emissions systems diagnostics has been completed. Although your BMW did not fail for high CO, CO amounts greater than 0.1 is considered high and a rich fuel condition may exist. 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