Just wondering where I should be looking if my emissions testing showed that my nitrogen oxide (NO) content was too high. I've been told to check the cat and the EGR system (including BPT etc). The rest of my emissions were clean, typically 1/6th of the max value for both carbon monoxide and hydrocarbons, so the problem is just with the nitrogen oxide content. Any ideas?
note: this is in CA with the new ehanced emissions test aka dynameter testing at 15 and 25mph.
rpm measured at 15mph was 1765rpm, %c02 = 14.7, %o2 = 0.3%, hydrocarbons was 20ppm with max allowed 118ppm and the average being 31ppm, co2 = 0.09% out of 0.75% max, with average being 0.10, and NO was 1248ppm out of 799ppm max with the average being 237ppm.
rpm measured at 25mph was 1757rpm, %c02 = 14.7, %o2 = 0.3%, hydrocarbons was 10ppm out of 93ppm with average 20ppm, co2 = 0.04% out of 0.63% max, with average being 0.09, and NO was 1218ppm out of 738ppm max with the average being 199ppm.
emissions testing showed NO too high.
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- Car: 1998 Nissan Altima (modded)
2003 Audi A6 2.7T (stock) - Contact:
no your egr isnt opening. the other readings are 2 good to be the cat they are well within the average of other 1989 240sx's you need to check the BPT hose below the bpt valve. also while the car is idleing push up on the diaphram in the egr from underneath the car should stumble or die if it does you know you have egr flow. check your vacum supply to the bpt make sure you have vaccum to it while holding throttle at 2000rpms. I suspect it is either the BPT hose under it has a hole burnt in it. or it has become so soft it is collapsed.
remember I am under the watchful eye of the california smog nazi's...lol Had to go through a semester of smog training in a state smog class and have 3 ase's including L1. IF I dont know what I am doing and they pop me for even repairing a car wrong I have to pay a hefty fine. and possibly be refferred for reschooling And I dont want that!:D
right on thanks Nistech. I was gonna have a poke around my egr and my bpt in the morning. just really bummed about it today to get around to it. Oh i took your rec and bent some of my injector plugs back into place (from way back) after I scraped off the crazy corrosion that happened to be on both the plugs and on the injectors which stabilized my idle very well. Now just this damn emissions thing I gotta wrestle with. Dammit.
hey Nistech, I've tested the egr by pushing up on the diaphram and yes the engine stumbled to nearly the point of death (thank god too, otherwise it'd be a total pain to get out). I've done a visual inspection on the hose that runs under the bpt, it looks fine from a distance, but I'll need to go at it a little closer. As a precautionary measure, I've taken the BPT from a pulled motor (my buddy did his sr swap already and left his 24E lying around) and gotten a new vacuum hose for the underside. Any recommendations on what to do to that bpt while it's out, like should I run any type of cleaners through it, replace the little vacuum hoses that run on the top side of the bpt, etc? Thanks again, I really appreciate the help.
oops forgot to tell you that when I race the engine, yes the EGR does go up, but only slightly and feels like it's just a brief amount of time that it's open also. Is there a rpm that I'm supposed to test it at? From your above post, I'm guessing I should have a look at the hose in the 2k rpm range to test the bpt and also to have a look to make sure that the egr is opening sufficently at that range probably at the same time? What would be a sufficent amount of valve movement for the EGR?
thanks again
thanks again
with the car at a stand still the egr will hardly move. even at 2000 rpms there is not enough flow in the exhaust to create enough back pressure to continuously operate the egr. you can sometimes substitute back pressure by clamping a 1 3/16 inch socket in your tail pipe then throttle it and see if the egr comes open and holds somewhat ,it will flutter a bit due to pulses in the exhuast. you need to confirm the egr valve is opening while driving since it is done on the dyno.
ah ok I see. Well I've got a pretty big exhaust on my car now, do you suggest putting in the silencer to close up the opening of the exhaust to 1.5 inch versus the 3 inch it's at now? Only other thing I can think of is to swap the license plate and the dash with a buddy who's got a completely stock s13 just that he's got a champagne colored coupe versus my red fastback. But yeah seriously I need to pass this smog check.
Alrighty Nistech, I got back from the smog check test again, and again it showed that my NOx content was still too high, this time around 900. I did have a slight problem with my egr, but that was fixed with new vacuum hoses (that dropped the NOx by ~300 points) and the silencer (reduced the opening to 1.5" with the silencer vs. 3"). The tech told me that the problem now probably lies with the AIV or the cat. That the AIV isn't letting air through to the cat or that the cat has just gotten too old (my car has 174k miles). I was then told that the AIV wouldn't be functioning if the reeds were not closed all the way, that they would not open at negative back pressure if the reeds were open enough to let a piece of paper through.
Now rewind a few months back, I did clean out the AIV reeds with castrol superclean and I forget if the reeds were slightly parted, but there's a good chance of it as I remember the reeds being black before, but were partially silver as a result of the cleaning. I do have access to another AIV though so I'm not too concerned about that part. However, if it does turn out to be the cat, would you recommend getting a catco high flow cat for CA emissions or should I just go to a regular muffler shop to get a replacement cat?
Now rewind a few months back, I did clean out the AIV reeds with castrol superclean and I forget if the reeds were slightly parted, but there's a good chance of it as I remember the reeds being black before, but were partially silver as a result of the cleaning. I do have access to another AIV though so I'm not too concerned about that part. However, if it does turn out to be the cat, would you recommend getting a catco high flow cat for CA emissions or should I just go to a regular muffler shop to get a replacement cat?
what did your readings all look like on your recent test? I kinda want to see if they changed with the egr repair.
Little back ground on how nox is formed and hopefully it will help you understand why your AIV would really not have and effect on NOx if it were not working. Since the air we breath is 78% nitrogen,21%oxygen,and 1 % other gases. the mix of gases enter the combustion chamber as part of the air/fuel mixture. NOx is created in the combustion chamber(typically) and is a result of pressure and heat exceeding 2500 degrees. What NOx is; oxides of nitrogen, multiple oxygen molocules combined with nitrogen molocules, what happens is when the combustion chambers temp is extreamly high and the piston comes up on its compression stroke at the moment of detination the oxygen molocules are fused to the nitrogen molocules. Then they are pumped out the exhuast .this is where the cat convertor comes in to play. if you have a single cat on your car then it is a TWC(three way cat) the front half of the cat is composed of a precious medal, rhodium,in this portion a chemical reactin takes place which seperates the oxygen from the nitrogen and sends the 2 into the next stage of the cat. the oxygen is used in that stage to combine with the HC and CO to create H2O and CO2 (harmless gases). The nitrogen is sent on down through the exaust at this point(unless the cat over heats and recombines the nitrogen to the excessive oxygen). now the cat is your post combustion NOx emissions eguipment. Your pre combustion equipment is your egr. the EGR(exhuast gas recirculation) this device is primarily used to cool the combustion chamber since the already burnt exhuast does not have any burning properties. there are few other things that can effect NOx but primarily it is a heat related gas so you need to address and issues that would cause you combustion chamber to exceed the 2500 degree threshold(sp?)
Timing as you asked before can cause high combustion temps but would have to be extreemly advanced. retarding it will bring it down but you cant exceed 3 degrees on either side of your timing spec.
Another condition could be engine temp. i.e. t-stat sticking,cooling fan clutch not locking up, restricted flow in radiator,ect... these would usually be seen in your temp gauge as running slightly hot.
high compression in your cyl's can also cause the problem which can indicate heavy carbon deposits on the cyl head and valves. what happens with these deposits is 1 it raises compression in the cyl but the other problem is carbon gets heated up during the detination process . Once it gets hot it does not cool down fast enough for the next firing sequince therefore raising cyl temp.
with that info it should explain how the AIV system not working would actually help NOx since it is not pumping air into the system. And it has no value in reducing NOx that system is to inject air into the oxidizing portion of the system(second portion of the TWC) now if the system was injecting air upstream all the time this may effect the first part of the cat since the first part is there to remove oxygen from the NOx molocules.
Little back ground on how nox is formed and hopefully it will help you understand why your AIV would really not have and effect on NOx if it were not working. Since the air we breath is 78% nitrogen,21%oxygen,and 1 % other gases. the mix of gases enter the combustion chamber as part of the air/fuel mixture. NOx is created in the combustion chamber(typically) and is a result of pressure and heat exceeding 2500 degrees. What NOx is; oxides of nitrogen, multiple oxygen molocules combined with nitrogen molocules, what happens is when the combustion chambers temp is extreamly high and the piston comes up on its compression stroke at the moment of detination the oxygen molocules are fused to the nitrogen molocules. Then they are pumped out the exhuast .this is where the cat convertor comes in to play. if you have a single cat on your car then it is a TWC(three way cat) the front half of the cat is composed of a precious medal, rhodium,in this portion a chemical reactin takes place which seperates the oxygen from the nitrogen and sends the 2 into the next stage of the cat. the oxygen is used in that stage to combine with the HC and CO to create H2O and CO2 (harmless gases). The nitrogen is sent on down through the exaust at this point(unless the cat over heats and recombines the nitrogen to the excessive oxygen). now the cat is your post combustion NOx emissions eguipment. Your pre combustion equipment is your egr. the EGR(exhuast gas recirculation) this device is primarily used to cool the combustion chamber since the already burnt exhuast does not have any burning properties. there are few other things that can effect NOx but primarily it is a heat related gas so you need to address and issues that would cause you combustion chamber to exceed the 2500 degree threshold(sp?)
Timing as you asked before can cause high combustion temps but would have to be extreemly advanced. retarding it will bring it down but you cant exceed 3 degrees on either side of your timing spec.
Another condition could be engine temp. i.e. t-stat sticking,cooling fan clutch not locking up, restricted flow in radiator,ect... these would usually be seen in your temp gauge as running slightly hot.
high compression in your cyl's can also cause the problem which can indicate heavy carbon deposits on the cyl head and valves. what happens with these deposits is 1 it raises compression in the cyl but the other problem is carbon gets heated up during the detination process . Once it gets hot it does not cool down fast enough for the next firing sequince therefore raising cyl temp.
with that info it should explain how the AIV system not working would actually help NOx since it is not pumping air into the system. And it has no value in reducing NOx that system is to inject air into the oxidizing portion of the system(second portion of the TWC) now if the system was injecting air upstream all the time this may effect the first part of the cat since the first part is there to remove oxygen from the NOx molocules.
Thanks for the write up on possibilties on my situation. I think I know what's causing it. I did lean down the engine a bit using my S-AFCII, I think I should richen up the mix by returning the values below 2500rpm back to ecu set levels instead of the leaner condition that was setup.
I wasn't told the other numbers when the mechanic at Ellis Brooks Nissan had a look at my car, but I was told that the NO was dropped down to about 900 after changing the vacuum hoses that ran the EGR system (from what I could see) and doing "all that he could" although I'm not too sure what that means.
Only other thing I can possibly think of is maybe cleaning my egr of it's carbon deposits and swapping out my AIV with a friends, richen back up the system, and then put the car back on the dyno. I've already taken SeaFoam into my car before, but perhaps I'll try that again since my vac lines were in bad shape.
I wasn't told the other numbers when the mechanic at Ellis Brooks Nissan had a look at my car, but I was told that the NO was dropped down to about 900 after changing the vacuum hoses that ran the EGR system (from what I could see) and doing "all that he could" although I'm not too sure what that means.
Only other thing I can possibly think of is maybe cleaning my egr of it's carbon deposits and swapping out my AIV with a friends, richen back up the system, and then put the car back on the dyno. I've already taken SeaFoam into my car before, but perhaps I'll try that again since my vac lines were in bad shape.
Im in the same boat! I bought a new cat, o2 sensor, plugs, fuel filter, checked operation of the egr, and set timing to 18 degrees btc. failed with 1400 nox! 200 more then before i changed the cat! Only other thing that I have been told to do is clean the carbon from the combustion chamber. I pulled the egr and noticed the hose on the bottom of the transducer was a little kinked. If it fails again after the combustion chamber cleaning im just going to go buy a safc and cheat! Is there any way to richen fuel with stock componets? Also any advise is welcome!
well im back again, I fixed everything but still no go.... nox is 1200 at 15 mph and 1400 at 25. I even disconnected a vacum line that has a higher vacum pressure then the one at the egr soleniod to hopefully make the egr open more. still 1200 at 15 and 1000 at 25mph. maybe the vacum source is weak?? What exactly creates the vacum for the egr system and where is it? Also I just read about cleaning the maf maybe that is the solution. Im goin to go call the previous owner and request that she pays for half of the repairs or take the car back. she lied to me when i was buying the car and said that she didnt smog it, when i went to go smog it the day after I bought it the tech said that it was smogged the day before! she lies!! SO I have this RB20det sitting in my garage waiting to go in as soon as i pass smog... what a beach. at this point it dosnt matter if i start all over again with another car, I just want to finish my swap!!:help
crxcess, do you have the most recent printout on your car?if so give me the numbers off it. all of them.
also if you give me your lic plate number I can run it through the state data base and see exactly how many times it failed over the last 2 yrs. the data base only tells me where it was smogged and weather it passed ,failed,or gross polluted. If you dont wanna post your plate on the boards shoot it to me through the email link in my profile. Any other info though like your test results post here in the thread. All technical info on your sitution should be posted in the thread for search reasons.
also if you give me your lic plate number I can run it through the state data base and see exactly how many times it failed over the last 2 yrs. the data base only tells me where it was smogged and weather it passed ,failed,or gross polluted. If you dont wanna post your plate on the boards shoot it to me through the email link in my profile. Any other info though like your test results post here in the thread. All technical info on your sitution should be posted in the thread for search reasons.
Nah not yet. Just got a stock muffler on my car not too long ago and got the registration extension till the end of feb. Got my parts aiv reeds and new 3" catco cat but the cat needs to get the flanges welded on and I've yet to go to the muffler shop to get that done since I'm waiting for the gaskets to arrive. Richened up my mixture a bit more too. Hopefully all that will get my nox count down enough for me to pass smog.