JRWalton

1989 CRX Si, 129K miles, Timing belt replaced at ~ 102K

Numbers from Emission Test
RPM %CO2 %O2 HC %CO NOx
15 mph 1811 14.9 0.0 82 0.35 283
25 mph 2051 15.1 0.0 30 0.03 877

The HC value at 15 mph is acceptable but on the high side, which indicates unburned fuel I believe. The NOx value at 25 mph exceeds the limits; the NOx value at 15 is lower than the 'AVE'.

It appears that high NOx (the failure) results from high combustion temperatures. Neither the 15 or 25 mph HC values suggest a lean mixture which could cause high combustion temperatures.

Since the vehicle does not have EGR, the likely components causing the results are the O2 sensor or the catalytic converter.

Thought??

4drEF

Has the o2 sensor ever been replaced? that would be my fist guess assuming you don't have anythign else going on like exhaust leaks or cooling system issues.

Might be worth your while to run Seafoam or similar product to decarbonize (before chaning O2).

JRWalton

Thanks for your response. Since the failure, I have changed the O2 sensor. I have not yet had the car retested. I was not certain that a defective O2 sensor would cause the engine to indicate too rich a mixture at low rpm and too lean a mixture at higher rpm.

I thought I would run some Sea Foam through it, and give it a good long run to decarbonize the cylinders to the extent possible.

acmoc

hydrocarbon unburnt fuel

NOX high temps
Exhaust leak causing lean running condition resulting in high combustion chamber temps and catalyst not heating sufficiently to burn up the unburnt fuel
Your o2 numbers are higher in the fail 25 mph run, indicating a leak.
Leak can also bring in air

What's the timing?

arries289

High HCs are indeed a fuel/timing issue. The high CO can be a cat converter issue. How old is the cat? What I would do is 1) verify the timing is dead at a proper idle rpm. 2) replace your spark plugs if they have more than 5K miles and make sure they are OE type. I run E3 plugs and have seen better emission results 3) run some seafoam (or similar) through the gas at highway speeds. 4) retest

If your timing has to be adjusted make sure you reset your ecu.