Matching You with a Pre-Screened Smog Check Center You will Love
Free Online Smog Check Diagnosis
$500 Free Consumer Repair Assistance
Failed Emissions Test
How to Pass the Test
Who Else Wants To Pass the Smog Check
Miles: 
Which Type Should I Choose?
 
            
    Forum > Failed Smog Test > Question

Join the community and post your questions. Ask-A-Tech right now!
 
 



Failed Smog Test
 

Why did my 1987 Buick Regal Fail for High NOx?

My Buick Regal just failed the NOx portion of the smog test . It measured 920 ppm. All other emissions passed. My Buick Regal also passed 2 years ago without a problem. The Catalytic Converter and Oxygen Sensor only have approximately 10,000 miles or less on them, so I know they are ok. The only major change I did was I added a billet throttle body which is approximately 25% larger than the stock throttle body. I'm wondering if this would dramatically raise NOx? Should I try a new O2 sensor?




Answer:  

The first component we'd suggest looking into would be your Buick Regal's EGR system. The EGR valve is the number one component used for NOx reduction. Second would be fuel control (oxygen sensor and MAP). If you have the engine running lean your going to come across high NOx issues. The larger throttle body is definitely not helping as well. Technically your Buick Regal's manifold pressure sensor should pickup on the difference of vacuum due to the greater amount of air entering the engine, however your Buick's ECU calibration may not allow the extended range.

We'd recommend ensuring the EGR system works, the EGR passages are free and clear of any carbon build-up. Second make sure your Buick Regal is in proper fuel control. This means the oxygen sensor is sending the correct signals to the ECU and the ECU is commanding the proper amount of fuel to the combustion chambers. And finally (if possible) replace the throttle body with the stock one.


posted by SmogTips Support 06-13-2013 08:56 AM
Get Your DMV Registration Sticker Quicker!
Covid 19 Impact - Option for DMV service without delay.
NeedTags - OL #89953. California authorized online vehicle registration service provider.


Related questions and answers you might find useful:

Chevy k10 1984 with a 1990 crate engine from out of state by Jonny on 06-20-2021 10:36 AM

1976 Jeep CJ7 with 304 V8 & AT components by Derek on 06-18-2021 03:59 PM

My question is in regards to something my neighbor told about having my 2004 GMC Sierra SLT Smog Checked! by Richard on 06-18-2021 01:46 PM

Jeep Wrangler Sport DMV Registration Is Due In 7 Days by Irack on 10-02-2020 04:18 PM

Do I Have to Smog a Vehicle I Want to Make a Non Op? by Natali on 03-28-2020 09:05 AM