92 240 need advise for emissions

[Wisconsin 240SX]

I flunked my emissions test today. I have a '92 240SX SE HB, 152K, all original including the exhaust and cat converter. It runs and idles perfectly, no problems at all. Did the Dyno test here in WI, NOX failed was 3.555 g/mile, limit is 2.0. HC passed at .2193, limit is .80.CO passed at 2.8, limit is 15.It had new Nissan parts 7K ago = wires, plugs, cap, rotor, etc.Any ideas ? Where can you get a less costly Nissan cat converter ?Thanks

[Q45tech]

NOx is primarily an EGR [dirty reduced flow] related problem if the HC and CO/O are low. HC/CO number says the cats are working somewhat considering their age/miles.

[Wisconsin 240SX]

Thanks for the reply. I did remove and clean the AIV valve afew months ago. It was very clean, no gunk, just a light dusting of black carbon. Any tricks in getting the EGR valve off ? It looks like it's in the back pretty tight ? I'll try and get it off and clean it or replace it.Sounds like replacing the cat may not help much.Any other ideas ?

[jacob360]

EGR problems are the most common causes of high NOx, but a lean air fuel mixture, overly advanced ignition timing, carbon buildup on pistons/combustion chamber, and running hotter than normal can all cause NOx emissions to elevate.

Open the EGR valve at idle with your figners or a hand held vacuum pump. There should be a significant drop in RPMs, maybe even stalling. If that doesn't happen, your EGR passages are clogged.

Watch the EGR pintle with a mirror and flashlight, or tee a vacuum gauge into the EGR vacuum hose. Rev the engine, the EGR should open, or you should get a vacuum signal. If it's a backpressure EGR (I have a 240sx, but haven't looked at my EGR yet), you might have to restrict the exaust to make it work. Use a big socket wrapped in a shop rag or a piece of wood.

[NISTECH]

you can clamp a inch and a quater socket into your tail pipe with vise grips to create back pressure. but when removing it use a doubled up rag cause it will be hot. if you have the hand help vac pump that has 2 ports on it you can also apply pressure to the bottom of the bpt to acheive the same effect. it takes about 2 psi to close the bpt.that aint much so a short quick squeeze from the pump is all you need. This wont tell you if there is not enough back pressure in your exhuast by doing it this way. best way to test for accurate back pressure is to drive the car with a vaccum gauge tee'd into your vac line between the bpt and egr. prop the gauge on your windsheild so you can moniter it during light to moderate accel it should climb to around 5 to 10 in of vaccumm.

[Wisconsin 240SX]

Where would be a good place to purchase the EGR and BPT ?I might as well replace them both and see if it sniff's any better.Thanks forthe help.I'm going to test the EGR tonight.

[Wisconsin 240SX]

I had a shop inspect the car and they found that the EGR solenoid was not working, replaced it, EGR working well, all pipes clean and not clogged. Took it back to re-sniff/ re-test the emmissions and it failed again with NOX about the same.Any ideas ? Would a new Cat converter help ?Thanks

[Wisconsin 240SX]

I had a shop inspect the car and they found that the EGR solenoid was not working, replaced it, EGR working well, all pipes clean and not clogged. Took it back to re-sniff/ re-test the emmissions and it failed again with NOX about the same or 2.35, just over the limit.Any ideas ? Would a new Cat converter help ?Thanks

[NISTECH]

what happen to your HC and CO readings also is there an O2 reading on the print out?

[Wisconsin 240SX]

No O2 reading on print out.HC= .3672 max is .80 g/mileCO=2.8998 max is 15.0 g/ mileNOx= 2.3382, max is 2.00 g/mileSo the NOx came down but not good enough.

[NISTECH]

check your timing. all other readings indicate everything else seems ok. also do a compression test on the engine if the compression is higher then spec this could also cause NOx. if these tests come out ok and your engine is not running hot. My best guess would be the precat is bad. the pre cat is what breaks down NOx the most. the second cat is just a back up. and this is providing you have a precat. some fed cars didnt.

[Wisconsin 240SX]

Thanks for the help. Can you retard the timeing and helpt the NOx ? I assume if compresion is high it would have carbon build-up, any way to remove wothout taking the head off ?The engine seems to run great, that is not hot, it runs very well with no problems at any speed even cruise every day for the last 7,000 miles at 70-80 mph.I dont think I have a pre-cat but only one cat converter, it's a '92

[NISTECH]

do you have purge air on your car?

you can have a decarb done at most dealers maybe even independants have the kits. but if your compression is ok it would indicate you dont have excessive build up in the cyl's. timing wont effect it that much unless it was overly advanced. here in cal timing is checked on the smog test. dont they do it there as well?

[Wisconsin 240SX]

Original owner had trouble passing emissions Feb. 2003, failed three times after spending $500 at dealer for tune-up. He then took it to a state run emissions dispute center where thet said timing was set at 28 deg......re-set to 20 deg which is spec and it passed fine.I have not tested timing, dont think it changed.I dont think I have a purge valve, it's a '92 non- Cal car.I'll fool with it later when it warms up, probably April.No in Wisconsin they do not look under the hood or even look for a cat converter but run the car on a dyno at slow spped then for some time at 50 mph......pretty strict test and probably as bad as Cal test.Thanks

[NISTECH]

actually the dyno test is about the same here in cal,but we also do functional tests and complete emissions visual inspections. if the timing is off more then 3 degress either way I have to fail it. if the check engine light even flickers while doing the test at any stage I have to fail it. if the fuel cap doesnt pass a pressure test I have to fail it. california test standards are extremely strict. right now they just implemented dyno testing in the bay area(san fransico area) and tons of people are failing for nox emissions since their cars were never tested for nox before. that is the additional pollutant mesured by a dyno test.