Questions and Answers
200-SX Failed Inspection
Q. Hi, I have a 1987 Nissan 200SX that has failed the enhanced emissions test three times now. This is the 2.0 liter 4 cylinder known as the CA20E motor with a manual transmission. Mileage is 338,000 although the engine probably has somewhat less than that as it is not the original engine.
Car runs extremely well. Starts instantly, idles fairly well, slight "hiccup" every few seconds, pulls strongly especially at highway speeds from 65 to 85, smooth, etc. Only mechanical deficiency that I am aware of is that the coil for the exhaust side bank of plugs (8 plugs, 2 coil system) is not firing and has not worked in 5+ years. Replacement power transistor only available from Nissan and, with coil, is well over $200.00. As the car runs so well without it I have resisted replacing it.
Catalytic converter is original as is everything else, EGR, etc. Temperature gauge barely registers so I plan to test thermostat and probably replace it. Could this affect emissions? I have not checked for any computer codes but plan to do that next. Car failed initially for HC and CO. Replaced spark plugs, O2 sensor, PCV and hose, air filter. Re-tested and car now passes for HC and CO but fails for Nox. Readings for oxides of nitrogen jumped from 1151 and 1278 to 2505. The standard is 1323. HC improved from 187 and 241 to 159 with the standard being 173. CO improved from 2.21 and 3.31 to .44 with standard being .98.
I was quite surprised to have fixed several things and have such an improvement in HC and CO but have Nox jump up so much. Any pointers? The inspector suggested the EGR valve and most of the advice on the web seems to be the EGR and replacing the catalytic converter. Thanks for any advice that you can offer. This is a low budget operation so anything that I can do to avoid unnecessary repairs is a big plus!
A. The reason Nissan used an eight plug, two coil system was to reduce exhaust emissions. At idle or under low loads, the exhaust coil fires the exhaust side plugs. Under hard acceleration, the exhaust side of the ignition system shuts off to prevent pinging. Since it is part of the emissions system, replacing it will lower your emissions. You don't have to buy a new one, you can get a used coil assembly from a junkyard for much less than a new one.
The Nox is most likely due to a bad EGR or clogged EGR passage. At idle, hook up a hand vacuum pump to the EGR valve and apply vacuum to open the valve. If the engine stumbles badly or dies, the passages are clear and the valve is working. If it is, check the vacuum switches for the EGR system.
Additional Information provided courtesy of ALLDATA
