Turbo sedan. Failed NOX. Here's the data.

1st column: Test; 2nd column: Reading, 3rd column: Limit


40 km/h

HC ppm 44 66
CO % 0.20 0.37
NO ppm 641 505

idle

HC ppm 24 200
CO % 0.06 1


Can one conclude anything in particular, based on the fact that HC and CO are well under the limit, but NO is above? For example, can I say one way or the other if I do or don't need a catalytic convertor? I'm surprised that the idle tests have laxer limits, yet my car performs better on them.

I know that high NOX relates to lean mixture / high combustion temperatures. Does high octane gas likely make for hotter or colder combustion temperatures? I put 1/4 tank of high octane in, just before the test.

Another thought. My tank pump isn't working. Is it likely that this would cause a lean mixture, hence NOX?

I usually do an oil change before the test. Didn't have time this time, but I guess with HC results passing, lack of an oil change is not a factor.

I believe that my peak turbo pressure is about normal. Given that this intake air system seems to sustain pressure, I guess that means that at least this portion doesn't have vacuum leaks. I suppose that any connections through check valves though could.

Anyway, unless someone thinks otherwise, my plan was to replace the catalytic convertor and hope for the best. Would hate to do this, however, and not have it cure the issue.

Thanks,
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David Armstrong - '86 240(350k km?), '93 940T(270k km), '89 240(parts source for others) near Toronto