Hey guys,

Took my Q45 (175K) to do the mandatory smog test a few days ago. Failed on NO (PPM). Measured results for my car were 552 at 15mph and 836 at 25mph. The max allowed are 475 at 15mph and 478 at 25mph. I was far from passing the test. Came back, searched NICO and found lots of advice on cleaning EGR and TB. Did that so that EGR and TB crystal clear. Then went back to retake the test. I got 670 at 15mph and 759 at 25mph. What is going on? Cleaning did not help at all. I am really confused. BTW, I ran BG44K about 500 miles ago.

Please advice on what should I do to pass this test.

Thanks,

Andre.

explain exactly how you cleaned the egr.

I took it out, unscrewed the metal hose that is attached to it. Cleaned the hose with a needle like object. Then cleaned the both ports of the EGR with screw driver to remove hard composites and then sprayed TB cleaner until it poured out clean. Then unscrewed the temp sensor and cleaned the passage to the TB with drill bit. It has some composites but it was far from blocked. Then sprayed with TB cleaner. Also took the entire TB out incleaned the part with TPS. Cleaned butterflies and passages with TB cleaner. I am not sure how these tests go but what if I did leave some deposits minor but that do not block the flow, would I still fail this test so badly?

Is it how I was supposed to clean it or have I missed something?

Andre.

What about the CO and HC? Borderline high or well within range? If the CO is high also you should look at the O2 sensors. Any idea if they're functioning properly? Spark plugs been changed lately? Was the engine hot for both tests?

Where in CA?

HC measured 23 at 15mph and 18 and 25mph where the max allowed is 56 at 15mph and 31 at 25mph. CO 0.01 at both 15 and 25mph with max allowed 0.30 and 0.32. No problems there at all. I live in Sunnyvale, south bay. The engine was hot for the test. Spark plugs are very old, I replace them maybe 7 years ago (probably drove 70K since then). Do you think spark plugs may affect this NO (PPM) test?

Andre.

I'm no expert on emissions and am a little nervous about taking my 90Q in next month for its biannual smog. Here's a good site that explains the reasons for failing HC, CO and NOx emissions.

http://www.smogtips.com/failed-emissions-test.cfm

Common causes of high NO are defective EGR, defective Cat, engine overheating and lean fuel mixture. If you haven't had a leaky or dying injector since the last smog inspection I'd rule out bad cats, you've cleaned the EGR system, and didn't mention an oveheating engine. That leaves lean fuel mixture.

Quote from the article- "Lean fuel mixtures cause high NOx. A lean fuel mixture exists when less fuel then required is delivered to the combustion chambers or when more air then necessary is added to the fuel. In either case the lack of gasoline needed to cool the combustion chambers down is not present. Combustion temperatures increase causing high nitrous oxide emissions. A lean fuel condition may be due to a vacuum leaks and/or defective fuel control components, such as the Air Flow Meter, Engine Coolant Temperature Sensor, and O2 sensors."

I'd clean the MAF and probably change O2 sensors if you've never done it. Do you know anyone local with an OBD-1 Consult cable that can check the O2 sensors?

I drove through Sunnyvale last weekend on our way to the Santa Cruz area. I had my laptop and consult cable with me.

I just went back to check the EGR again and noticed that I forgot to tighten the o-ring on the TB when I cleaned it a few days ago. Darn it!!! I think it was leaking air "after" MAF which most likely caused the engine to run lean. It is exactly to your point .

Maybe I should re-test it now ...

Andre.

also make sure your EGR valve is opening. when warm, bring the revs to 1500 and hold your fingers on the underside of the diaphragm, you should feel it pulsing.
the right angle passage for the EGR at the bottom of plenum can be difficult to clean out (you have to go at it from both directions to get clean enough.

as a reference point, my last smog on the 94 in CA (Aug 2008), the NOx was 7ppm. It actually got cleaner each time with more aggressive maintenance. No smog checks in FL, but i'm willing to bet i have the cleanest burning 17yr old V8 in these parts....

I passed the test . What I did was tightening that o-ring and putting another BG44K. With BG44K I drove maybe 20 minutes really aggressive on the highway. I got on NO(PPM) close to 250 on 25mph test and 450 on 15mph test. Which compared to my previous test is almost lower by x2 on the 25mph test and barely under on 15mph test. Not sure which of the two things helped the most (tightening o-ring or BG44K) but glad to be done with it.

Thanks to everyone who contributed to this post.