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SMOG on a Honda - "NO" issue

87 Integra

Car was taken for Test only

It failed on “NO” at 25mph - passed at 15mph

Instead of NO coming down with speed, it went up.

Other than NO, all measurements were perfect.

Any tips to get this fixed?

Have your codes read. It will probably turn out to be a bad 02 sensor. There can be other causes but it sure sounds like a bad 02.

Check and make sure the EGR circuit is functioning correctly. If it’s not, it’ll result in high NOx readings.


Tester, there is no knocking on the car

Does it mean no issue with the EGR?

Listen to tester, he’s right. The knock sensor keeps it from knocking.

Sounds like an EGR problem to me. You cannot use a blanket statement of no knocking to cover all cars or even all cars of the same make, model, and engine.

Variations can even be due to improper ignition timing since this car should have a distributor. Any improper adjustment of the timing and timing alterations during a timing belt change can throw things off.

Whenever oxides of nitrogen are concerned, we think EGR system. EGR was invented for that specific reason, lowering oxides of nitrogen.

These are the readings:
Max values are in parenthesis.

15mph 656 (760)
25mph 678 (542)

2 yrs ago it was
15mph 825 (835)
25mph 365 (774)

HC/Co #s are good, which are at 15 & 25 mph
22 & 11 for HC
.06 & .01 for CO

A mechanic (w/o testing the car) said cat
Integra forum said Cat

I am not a mechanic _ never had such issue before either!
In line with EGR, it does idle rough - its been doing it for a while - yet passed SMOG in the past.

Does an Integra even have a EGR valve? I see EICV (electronic idle control) valve?

I checked the manual - its the first place to look for!

A reliable source tells me faulty O2 sensor would give high HC readings too - which is not the case.

So now I am going for EGR valve - trying to clean it.

In the past, it BARELY passed NOx testing levels. So, in the past, the EGR system has been marginal. The EGR system needs testing and repair. The EGR system is the problem.

Does an Integra even have a EGR valve? I see EICV (electronic idle control) valve?

Probably. My 1979 Mazda GLC and 1984 Ford Fairlane both had EGR (and I had to fix it on both of them at about 70,000 miles).

Another reason to suspect EGR is stuck off (or that the passages are plugged) is that the car passes NO at 15mph when the EGR valve would probably be closed anyway.

Can’t locate the EGR - no parts shop has it but a gasket.
Not sure if the Cat is a 3 way and therefore no need for a separate EGR

Does Not have EGR valve.
Does not appear to have a 3 way Cat either.

Seems O2 sensor or the Cat.

Took the car to a Gold station for repair.
They did the pre-smog and it passed Nox: 752 & 515 (HC: 85/36 & CO: .27/.04)

So no repairs were done - they did the smog and gave me the certification: Nox 759/468

This car only does 2k miles/year - perhaps it wasn’t warmed up last time!

The CA BAR offers $400 to SMOG failed cars - I was asked about trying to improve the emission - I did decline as it already passed. Any thoughts?

My only thoughts are that I’m glad you passed and I suspect that if you keep the '87 for a few more years you’ll want to save for a new catalytic converter.

Cat converters reduce NOx levels by putting the molecules in direct contact with hot platinum-paladium (in the family rhodium). That weakens the bonds and allows the molecules to seperate into nitrogen and oxygen again, as they are in the air we breath. The platinum-palladium is coated over a honeycomb shaped ceramic substrate through which the exhaust gasses pass. All engines produce som elevels of NOx, especially when the cylinders get hot.

Over the years, carbon in the exhaust stream can accumulate on the surface of the magic metal and reduce its ability to perform its function by reducing the direct contact it has with the NOx molecules. I suspect that erosion of the magic metal occurs too, although I’ve never read this anywhere.

In cars model years 1996 and newer, there’s a second oxygen sensor after the converter the signal of which can be compared to the oxygen sensor in front of the converter and degradation of the converter’s function can be (and is) monitored by conparing the signals. Your '87 doesn’t have this ability, so there’s really no way to measure the efficieny of the converter.

In all honesty, in an '87, high NOx readings on a good running engine would send me straight to the converter.

Thanks MountainBike;
During the next 2 yrs, if I can get an all-electric conversion kit, I would convert it - it would beat Nissan leaf - Electric Integra!

Any key businesses that are doing such conversion (not necessarily for an Integra) that anyone can recommend to me?