Trying to figure out what causes to fail the NO (ppm) test on my kid's TOYOTA 1987 MR2

%CO 14.6 & 14.7
%O2 0.3 & 0.2
HC (ppm) 33 & 25
CO (%) 0.01 & 0.03
NO (ppm) 1115 & 735 max 825 & 764
failed the 15 mph test and barely passed the 25 mph test.

I also was told that the timing was of by 10 degrees, retarded I think but not positive.

Don't know what causes the NO emmisions, the cat was repalced two years ago, the car uses a quart of oil every 1k miles.

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Thanks, Juan

Check to make sure the EGR system is working. My guess would be a leaking EGR vavle.

I'll check that, anything else???

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Thanks, Juan

The oil consumption has probably killed the catalyst. The phosphorus in the oil (antiwear additive) is a permanent poison. 1qt/1000 miles is a LOT of oil consumption for that small engine.

You MIGHT try a high speed/high load 'burn-off' attempt on the catalyst before changing it. Also be sure the timing is right on, the EGR valve, plumbing, and passages are clean and working properly.

High NOx readings mean combustion temps are too high. EGR reduces combustion temps so start with that. If the spark timing was 10-degrees too advanced that might contribute to high combustion temps as well.

The folks at www.club4ag.com might have specific information.

Sixto
95 S420
87 300SDL

Thanks for your replies, what do you mean by high speed high load burn off? 1 hour drive or longer?

The cat was replaced 2 years ago but I see what you mean.

I will take apart the EGR system and inspect it well.

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Thanks, Juan

If the engine has EGR check the valve function and control system.

Also, properly check and understand what the timing is relative to spec. You may have to short a couple of leads on the diagnostic connector to get a true initial timing value. Look on the emission control decal or get a shop manual. The timing is supposed to be measured as part of the test and recorded on the report.

Retarding the timing will reduce NOx since it reduces peak combustion temperature, and the CA inspection places no limit on how much the timing can be retarded from OE spec.

I doubt if there is anything wrong with the catalyst given the low HC and very low CO.

Duke

%CO2 14.6 & 14.7
%O2 0.3 & 0.2
HC (ppm) 33 & 25
CO (%) 0.01 & 0.03
NO (ppm) 1115 & 735 max 825 & 764

CO2 is relatively low comparing to a very good engine, EFFICIENT AND COMPLETE COMBUSTION (15.2 TO MAX 15.6).

O2 is high and CO is very low indicates lean mixture. Low CO may also leads to low catalyst converter efficiency. Air leak past the air metering stage?

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Shane83SD

great information, thank's.
Now what to do about it?

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Thanks, Juan

Check the spark plug. If the insulator is white and/or blistering (normal is light tan), the engine is running lean and hot.

Possibilities:
Air duct leaking from air metering device to the intake manifold.
Leaking intake manifold gasket.
Throttle plate shaft leaking (loose).
etc., etc

Search the archive for leak detection techniques.

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Shane83SD

Ok, I will start by looking at the EGR valve and plugs.

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Thanks, Juan

egr valve and tubing good and clear, plugs white deposits.
running lean.

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Thanks, Juan

Juan,
I concur with all the above comments and advive so no sense repeating. EGR is the major contributer to reducing nitrous oxides and nitrogen dioxides, so be sure the system is funtioning. Apply vacuum to the valve at idle and make the engine run rough or die. Then hook it all up and observe that the EGR needle moves as you race the engine. You can tweak CO up a bit and that will also help. If you have an air pump, it plays a minor part, so make sure it works. Also be sure you are using the grade of fuel the car calls for. If the car calls for premium, combustion temps will increase with faster burning lower grades. All in all I thought those readings were good across the board and NOX isn't that far off. In fact I had a 90 300SEL in the same boat last month and tweaking the CO up got it through.

Good luck,
Peter

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Auto Zentral Ltd.

Thanks Peter, the car does not have an air pump. I will check the timing which I should have done before I took the EGR system apart.
How do you adjust the CO?

I will also fill up with higher grade gas. I have the "cheap stuff" in it right now. No such thing in the Bay Area as you know.

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Thanks, Juan

Sorry Juan,
I know nothing about Toyotas. We pay more for gas than anyone in the country. When they were doing live reporting on that DC serial sniper, I wasn't paying any attention to the reporter. My eyes were fixed on the Shell station behind her with the rediculously low prices.

Peter

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Auto Zentral Ltd.