Legacy Posted December 13, 2003 Share Posted December 13, 2003 I am once again calling on the collective experience of the group here. I recently attempted an emissions test with my 91 Legacy 2.2 (naturally aspirated). Surprisingly, given its mileage (210,000 km) it passed the hydrocarbon and carbon monoxide tests with flying colours, even at idle. The results were no where near the limits. However, for NOx, it failed miserably. My limit was 777 ppm and I got 1275 ppm. The mechanic said this high NOx reading is usually caused by high temperatures. He further suggested it could be because of a faulty O2 sensor running lean or the catalytic converter being shot. I happen to know that the car has no cat (the rear one was removed by the previous owner). I wanted to get some advice on what would cause the high NOx. I currently have no codes, having recently replaced the purge solenoid and cleared the code that it was causing. Thanks for any help Quote Link to comment Share on other sites More sharing options...
northguy Posted December 13, 2003 Share Posted December 13, 2003 Use the search function on this as there are numerous threads about this problem. In fact, edrach has written a couple himself which are about as good of a guarantee as you can get. Quote Link to comment Share on other sites More sharing options...
Legacy777 Posted December 13, 2003 Share Posted December 13, 2003 subaru uses a two stage cat converter. So if the previous owner removed the second cat and left the front one, the catalyst system is not complete and not properly doing its job. You could put a generic one on in place of the second one, and that should work fine. The guy was right, NOx is high heat, and the possible causes he suggested are on the money. You might be able to run some special cleaner through which would help you pass. Quote Link to comment Share on other sites More sharing options...
Legacy Posted December 16, 2003 Author Share Posted December 16, 2003 Turns out the front converter is the actual converter. The second one (back) is a resonator. The mechanic called the dealership and gave them VIN to confirm. (there may be differences in the US and Canadian systems) He has since done a diagnostic and gave me two options: the converter or removal of carbon build-up. The converter is quite expensive (over $300) on its own, but if I let him remove the carbon and it fails the retest, changing the converter would put me over the Repair Cost Limit, so I will get a conditional pass. This conditional pass is good for 2 years (when the next test is due). After that I can either fix whatever is required or sell the car and pass the problem on to someone who wants to deal with it or someone who lives outside of the emissions-test areas. If I can get 2 more years out of this car I wil be happy. Quote Link to comment Share on other sites More sharing options...
outback_97 Posted December 16, 2003 Share Posted December 16, 2003 Disclaimer: I have little knowledge of the emissions systems but this sounds a LOT like a situation we had and subsequently resolved. edit: removed lengthy EGR problem description per Legacy777's statement on the lack of EGR valve on these MY's. Sorry folks, it just sounded too similar to the problem we had with our '89 and NOx. Steve Quote Link to comment Share on other sites More sharing options...
Legacy777 Posted December 16, 2003 Share Posted December 16, 2003 I honestly doubt they are different from the US & canadian models. Everything I have read says it's a two part cat system....regardless what the dealer says. I'd probably do what you suggested and go with the carbon clean up even though it probably won't do much. The 90-94 legacies did not have egr valves btw.... Quote Link to comment Share on other sites More sharing options...
Supaglu Posted December 16, 2003 Share Posted December 16, 2003 Hi, Subaru's in the Uk use "three way" catalysts - and consist of two cats, the front one I believe is the two way cat and the second one is a "one way"cat. If the US subie's are the same and I believe they probably are then if you have the rear cat missing on your vehicle then the catalyst system is not removing all harmful gases. Regards Dave H Quote Link to comment Share on other sites More sharing options...
Legacy Posted December 17, 2003 Author Share Posted December 17, 2003 Did the carbon cleanup, brought the NOx down and squeaked by. Good for another 2 years. Quote Link to comment Share on other sites More sharing options...
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