This is topic Failed Smog in forum Tech Talk at Northern California Ford Owners .
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Posted by skeletor1987 (Member # 6597) on
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hey guys,
been a while since i posted on here. its finnaly time to sell my 1987 mustang lx hatchback. but when i went to smog it....it failed the NO portion. by almost 200. not too happy about it. i recently converted it from speed denstity to mass air, so the first thing i plan to do is change it back to speed density. then replace the o2 sensors as it suggested in the manual. anyone else have any suggestions?
Posted by CagedBlueGT (Member # 9804) on
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Id say just replace the 02 sensors and try a different stock h-pipe. Seems your cats are bad.
Posted by Adam5.0 (Member # 6995) on
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nox has to do with the egr system. check the egr valve first. if every thing checks out there might be alot carbon build up on the pistons. sea foam it.
Posted by CobraCoupe (Member # 7233) on
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^^^^+100
Posted by triple b (Member # 8763) on
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+1 cats just do two new ones it will pass with flying colors
Posted by bentley mobs a stang (Member # 11119) on
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A quick test to tell if Ur egr flows correctly is to idle the car and push the bottom of the diaphragm upward (be careful no to damage it).The engine should stumble, but not quite die like a Honda or something would. If not then the egr passages in the manifold are clogged. To test cats, I drill a hole before the first cat on each bank and stick a probe in to see what my exhaust readings are, then I compare the readings before and after the cats, if nox doesn't drop a shit ton after going through the cats, then the reduction part of Ur cats isn't doing its job, and need replaced. If u don't have access to an exhaust analyzer at a school or something, any smog and repair shop can and should know this test already, its the only real way to diagnose nox problems. If Ur in the bay area lemme know cause I work for a smog and repair shop, and we could diagnose it for u. One other simple thing to check is ignition timing. If ur timing is too advanced, it can cause high nox due to detonation. Good luck and lemme know what u find out
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