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High NO at 15mph - everything else is normal on Acura

Acura Integra 2000
15mph 467 67 693
25mph 754 62 8

The 693 failed my car smog. It was run for a total of 12miles that day, 4 miles average x 3 trips.

Is it just wasn’t warmed up properly?
Any tips to resolve this issue?

Yeah, 4 miles at a time isn’t enough to warm the engine up. That could fail it, but I’m curious as to why the smog testing shop even conducted the test on a car that wasn’t up to temperature.

High NOx is caused by elevated combustion temperatures.

Some of things that can cause high NOx readings are, a malfunctioning EGR system, an engine that’s running too hot, an engine that’s running too lean, high carbon deposits in the combustion chambers, and a defective catalytic converter.


I am going to use

Also, is it better to use 91 Gasoline than 87 I usually use?

Maryland tells us to drive for at least 20 minutes continuously on a highway before getting the emissions test. You might try that and see if it helps. As for octane rating, what doesn’t Honda tell you to use? Is premium recommended or required, or is regular recommended?

As per manual, 87

Using higher octane gasoline will have no beneficial effect.

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What were you HC readings? What’s weird is that you have really high NO at 15 mph, but hardly any at 25mph. That has to be some kind of important clue. Suggest to use a timing light to verify the ignition timing vs rpm curve is working to spec. Your idle advance may be too much.

Speed HC(ppm) NO(PPM)
15mph | 61 9 10 | 467 67 693
25mph | 45 6 7 | 754 62 8

Last smog test, 2 yrs ago - NO readings were (barely passed at 15 mph):
15mph 462
25mph 34

What is going on to my car? All the readings were much lower this time around except NO.

I went and checked the records all the way to 2013. This has has high NOx at 15mph - but this time, it exceeded the pass limit! I am puzzled.

I did valve adjustments recently - changed the O2 sensor as a precaution.
It has 130k miles on it

Your HC levels are excellent. The only problem is that pesky 15 mph high NO reading. Could be a faulty cat, but it seems like if it were the cat it would show up more at 25 mph, not 15 mph, as the cat would have to process more volume flow of exhaust gasses at 25 mph.

Idea 1: If you think the engine isn’t any hotter at 15 mph vs 25 mph, I’m thinking then there’s a problem with the EGR or the EGR modulator function. The EGR valve is commanded to open a varying and precise amount depending on the operating condition. On my Corolla there’s a thermistor on the EGR valve that is used to estimate the amount EGR flow, so the computer can turn on the CEL if the EGR valve isn’t opening as much as it is being commanded to. Perhaps that is what is happening to your car, the EGR valve isn’t opening enough at 15 mph, but at 25mph is opening the exact amount it should. Maybe your engine has no way to know the actual EGR flow. This sort of makes sense, the valve opens ok when it opens wide, but isn’t able to open a small amount accurately, maybe b/c it is sticking.

Idea 2: Ignition timing at 15 mph is overly advanced for some reason. Double check that.

@George_San_Jose1 and others:
I checked the historical records on SMOG.

2005 @15mph, NOx 126 @40k miles
– no records
2011 @15mph, NOx 246 @77k miles
– 2011 timing belt was done @80k miles- m/c said he tuned it then
2013 @15mph, NOx 442 @91k miles

Does the tuning needs to be redone? Or Sparks (NGK platinum was put in prob at 65k).

A basic tune-up always makes sense whenever there’s an emissions problem to solve. may not help, but couldn’t hurt. On your car – assuming there are no diagnostics codes – that would probably include

  • new spark plugs
  • new engine air filter
  • check/adjust valve clearances

Since fuel injection, tune-up is a mystery for me - I know they also use timing gun - timing was also checked in California SMOG test - it says

  • “Ignition timeing - Pass”

Just came back replacing the air filter which was in fact dirty.

spark plugs is what remaining - I remember the m/c told me that SP that was replaced with Platinum was good and asked me to keep it - seems to last 60,000 miles?

But if sparks are bad, then all or most reading would be bad, right?

I think they only check the base timing (timing at idle rpm). If there was a timing problem at the rpm corresponding to 15 mph they might not be looking for that during an emissions test. I can’t speak to your spark plug issue b/c I use conventional ngk spark plugs (i.e. not platinum) which only cost $2-$3 each and are very easy to change. So I always replace them before an emissions test as a matter of standard practice. I did find that a particular version of the ngk plug seems to work better for me at emissions time, they call it the “v-power” version, and that’s what I use now.

Have you checked that all EGR ports and passages are clear?
And that the EGR valve is clear and moving smoothly?

I do not where it is!

It does not seems to have an EGR (from factory)!,2000,integra,1.8l+l4,1366488,exhaust+&+emission,egr+valve,4968