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93 Altima Emissions fail on high Nox and HC

For details click on "More Details" at Aircare.ca "Inspection Info" -> "Test Results" VIN is 1N4BU31C1PC166601

Mileage is in km's Passing values are: HC .5 CO 9.3 Nox 1.24 Last test: 0.70 4.07 2.96

Last pass in 2007 was accomplished by installing a new aftermarket cat. The last test was after cleaning blocked EGR exhaust passage and replacing a split vac hose to the transducer. I still don't think the EGR is working right as there is almost no visual movement of the valve at approx 2-3000 rpm but there is a spike in vacuum at the hose connected to the valve, then it drops off right away while maintaining 2-3000 rpm. The valve itself holds vacuum and the engine stalls at idle if I manually open it. Should there not be a steady high vacuum at higher rpm's thereby keeping the valve open?

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mark
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Here's a graph of the last 2 fails and last pass: ctl + to enlarge

formatting link

Reply to
mark

if you're getting a spike in applied vacuum and the valve diaphragm holds, but there's poor activation, then there has to be a leak in the hose system somewhere. at which end are you measuring the vacuum? and don't forget that in neutral, you're no load, so operation won't be the same as on the dyno where the vacuum regime will be completely different.

as for the results, high HC and low CO are typically ignition problems. but only if the cat is failing - you wouldn't get the high HC if the cat was good.

aftermarket cats just don't last - that's why they're cheap. 2007 is plenty old for those things.

Reply to
jim beam

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