Smog test fail, Catalytic convertor or what?? Options

[bigredcelica]

Hi,
I have 1994 St202 Celi with a 3S GE injun with 90K miles. I have recently got a NCT test (Irish road worthiness test) which includes a similar test to the smog emmissions test. My low idle (1000 revs) showed fine but my high idle (2750 revs) came in over spec. The standard is 0.3 where my results were 0.4 These are ppm results, or a multiple of, for CO or Carbon Monoxide.

I brought this to a garage where the emmissions showed results of 0.005 for high idle but as soon as the revs were dropped the result shot up massively for a few seconds. He tells me that the cat is gone (nine lives my ass). Is he right? I wouldn't be very trustworthy of his business and need verification before buying. I don't partiucularly want to go down the road of adding Ethynol or such like to the fuel just to pass - I would rather get the car as it should be.

Any thoughts?

[GeEkBoY]

90K on the clock is not much for a cat, unless your car had problems in the past. The O2 sensor measures the Oxygen levels in the exhaust after the cat. The ECU tries to keep minimal levels of O2 in the exhaust. If there is too much O2, you will have N0x and CO, if there is too little O2, then you will have high hydrocarbons. The sensor could be reading levels off so there is not enough O2 in the mixture, or it could be slow to pick up changes when the inflow of air changes. O2 sensors are easy to change and less costly than a cat. If the one you have from the MR2 cat is the same switch it out and see if that changes the readings.

The next most likely cause is part of the cat has gone, cats have 2-3 different sections (this may have changed recently) there is a section for converting hydrocarbons into water and CO2. and other for NOx and CO. One of the sections of the cat could be gone while the other is still good. This is less likely a cause but still possible.

The other possibility is in the measurement of airflow into the engine. The sensor could be giving bad reading and the engine mixes up the flow of air into the engine.

You are pretty close to passing, so using the above mentioned additives to help you pass would be a good idea.

good luck and let us know what happens.