Help - failed smog test - Nox too high

87mk1gold · 08-04-2009, 02:16 PM

Passed every part but the oxides of nitrogen was just over the limit. The rest was well within limits. The engine runs so great it is hard to believe there is anything major wrong. Pulls hard all the way to redline, so I wouldn't think there is a fuel supply shortage.

I checked all the cooling fans, the timing, and the egr function. All seems to be good. The engine has a lot of miles on it, so it could be carboned up, but what could I do about that?

Only thing I can think of is the catalytic converter. It is a three way so it is supposed to control Nox as well, but replacing it isn't cheap, and I'm not convinced that's the problem. The other tested values were good.

What else is there?

David · 08-04-2009, 02:25 PM

You could always move to Florida.

No tests! I'm not sure of any way to clean the carbon from inside the engine short of a rebuild, but that's not really worth it on a good engine.

tstoney82 · 08-04-2009, 02:31 PM

here in NC we used to do those test a lot and i used to have to fix these types of issues so here is my 2 cents........

a good fix for carbon build-up is seafoam. go to the parts store and get two cans. (i think they are about 16 or 20 oz) put a full can in the gas tank with a full tank of gas and with the other do the following:

1. disconnect one side of one of the vacuum lines going into the intake manifold. make sure you dont disconnect the side that is connected to the manifold, but the other side.
2. let the vacuum from the line suck the contents of the second bottle out. you will also have to keep the engine revving about 2000 rpm to keep it running. dont let it suck too much at one time or else it will create problems.....just let it take in a little bit.
3. there will be smoke.....thats normal. the check engine light may even come on.....again normal....
4. when its done, reconnect the vacuum line and drive the car for about 30-40 miles to "purge the system". if you notice large smoke clouds its ok....its gonna happen. its just carbon being burned. make sure you rev it high a few times while driving to allow it to clean good.
5. after that is all said and done and the CEL (if it came on) is off, go get your test done again.

might cost a total of 15-20 bucks.

David · 08-04-2009, 02:34 PM

I always wondered how seafoam worked.

tstoney82 · 08-04-2009, 02:35 PM

its good stuff. ive used it several times and ive never had any problems with it. it will also increase your mpg slightly.

Medusa · 08-04-2009, 04:47 PM

I'm not saying I don't believe you, because I know nothing about Seafoam, but the whole "check engine light may come on, you have to rev the engine to keep it running" sounds sketchy to me. And I have also heard of probably three or four different ways to use seafoam.

Again, I'm not saying you are wrong or anything, it's always just seemed sketchy to me. But I've never seen it used or used it myself so I wouldn't know.

tstoney82 · 08-04-2009, 04:56 PM

Quote:

Originally Posted by Medusa

I'm not saying I don't believe you, because I know nothing about Seafoam, but the whole "check engine light may come on, you have to rev the engine to keep it running" sounds sketchy to me. And I have also heard of probably three or four different ways to use seafoam.

Again, I'm not saying you are wrong or anything, it's always just seemed sketchy to me. But I've never seen it used or used it myself so I wouldn't know.

the check engine light may come on due to the air/fuel reading it gets when the burned seafoam goes through the exhaust and past the o2 sensor. i guarantee if you where to check the code afterward it would be an o2 sensor code. the good thing is, the o2 sensor gets cleaned too.

the engine has to be reved up because if its not, it will essentially flood the engine with seafoam. any company that does fuel injection cleaning services will keep the rpm's steady at 2g's just for this reason.

i wouldnt recommend something i wouldnt do myself. i know you arent saying im wrong or anything, but i believe you should try it. you might be surprised with the end result.

TomsMR2 · 08-04-2009, 06:00 PM

your o2 doesnt get cleaned.. it gets badly contaminated by the seafoam. your plugs too. seafoam works, and i believe its pretty good stuff.. but plan on changing your plugs and at least burning your o2 sensor clean. mr2 o2's only last about 30-50k anyway, chances are its a good time to just replace that too.. but still, that unrelated to the NOx problem.

your EGR valve is plugged. its a common problem. you need to remove it and scrape it clean. also clean the manifold holes.

87mk1gold · 08-04-2009, 07:46 PM

Tom - That was what I thought too - but I took the EGR off, and checked it and the tubes into it and out of it, and it wasn't clogged. I ran some wire through everything just for good measure, but I've seen clogged EGR's before and it wasn't.

I used my shop manual to do all the tests they described on the EGR system, and it passed.

Next idea?

08-04-2009, 02:16 PM	#1 (permalink)
87mk1gold Ex Cortina Driver Join Date: Jan 2008 Posts: 9 Thanks: 0 Thanked 1 Time in 1 Post iTrader Rating: (0/0% )	Help - failed smog test - Nox too high Passed every part but the oxides of nitrogen was just over the limit. The rest was well within limits. The engine runs so great it is hard to believe there is anything major wrong. Pulls hard all the way to redline, so I wouldn't think there is a fuel supply shortage. I checked all the cooling fans, the timing, and the egr function. All seems to be good. The engine has a lot of miles on it, so it could be carboned up, but what could I do about that? Only thing I can think of is the catalytic converter. It is a three way so it is supposed to control Nox as well, but replacing it isn't cheap, and I'm not convinced that's the problem. The other tested values were good. What else is there?

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08-04-2009, 02:25 PM	#2 (permalink)
David Take a picture trick! Join Date: Jun 2007 Location: Tampa, Fl. Posts: 1,303 Thanks: 111 Thanked 25 Times in 25 Posts My Google Map iTrader Rating: (4/100% )	You could always move to Florida. No tests! I'm not sure of any way to clean the carbon from inside the engine short of a rebuild, but that's not really worth it on a good engine.

08-04-2009, 02:31 PM	#3 (permalink)
tstoney82 shop bitch Join Date: May 2009 Location: clayton nc Posts: 395 Thanks: 11 Thanked 7 Times in 7 Posts iTrader Rating: (3/100% )	here in NC we used to do those test a lot and i used to have to fix these types of issues so here is my 2 cents........ a good fix for carbon build-up is seafoam. go to the parts store and get two cans. (i think they are about 16 or 20 oz) put a full can in the gas tank with a full tank of gas and with the other do the following: 1. disconnect one side of one of the vacuum lines going into the intake manifold. make sure you dont disconnect the side that is connected to the manifold, but the other side. 2. let the vacuum from the line suck the contents of the second bottle out. you will also have to keep the engine revving about 2000 rpm to keep it running. dont let it suck too much at one time or else it will create problems.....just let it take in a little bit. 3. there will be smoke.....thats normal. the check engine light may even come on.....again normal.... 4. when its done, reconnect the vacuum line and drive the car for about 30-40 miles to "purge the system". if you notice large smoke clouds its ok....its gonna happen. its just carbon being burned. make sure you rev it high a few times while driving to allow it to clean good. 5. after that is all said and done and the CEL (if it came on) is off, go get your test done again. might cost a total of 15-20 bucks.

08-04-2009, 02:34 PM	#4 (permalink)
David Take a picture trick! Join Date: Jun 2007 Location: Tampa, Fl. Posts: 1,303 Thanks: 111 Thanked 25 Times in 25 Posts My Google Map iTrader Rating: (4/100% )	I always wondered how seafoam worked.

08-04-2009, 02:35 PM	#5 (permalink)
tstoney82 shop bitch Join Date: May 2009 Location: clayton nc Posts: 395 Thanks: 11 Thanked 7 Times in 7 Posts iTrader Rating: (3/100% )	its good stuff. ive used it several times and ive never had any problems with it. it will also increase your mpg slightly.

08-04-2009, 04:47 PM	#6 (permalink)
Medusa Cage Fighter Join Date: Sep 2008 Location: Reno, NV Posts: 630 Thanks: 9 Thanked 10 Times in 10 Posts iTrader Rating: (0/0% )	I'm not saying I don't believe you, because I know nothing about Seafoam, but the whole "check engine light may come on, you have to rev the engine to keep it running" sounds sketchy to me. And I have also heard of probably three or four different ways to use seafoam. Again, I'm not saying you are wrong or anything, it's always just seemed sketchy to me. But I've never seen it used or used it myself so I wouldn't know.

08-04-2009, 06:00 PM	#8 (permalink)
TomsMR2 Formerly Tom Brokaw Join Date: Feb 2005 Location: Bay Area Posts: 2,497 Thanks: 8 Thanked 233 Times in 168 Posts Blog Entries: 1 iTrader Rating: (0/0% )	your o2 doesnt get cleaned.. it gets badly contaminated by the seafoam. your plugs too. seafoam works, and i believe its pretty good stuff.. but plan on changing your plugs and at least burning your o2 sensor clean. mr2 o2's only last about 30-50k anyway, chances are its a good time to just replace that too.. but still, that unrelated to the NOx problem. your EGR valve is plugged. its a common problem. you need to remove it and scrape it clean. also clean the manifold holes.

08-04-2009, 07:46 PM	#9 (permalink)
87mk1gold Ex Cortina Driver Join Date: Jan 2008 Posts: 9 Thanks: 0 Thanked 1 Time in 1 Post iTrader Rating: (0/0% )	Tom - That was what I thought too - but I took the EGR off, and checked it and the tubes into it and out of it, and it wasn't clogged. I ran some wire through everything just for good measure, but I've seen clogged EGR's before and it wasn't. I used my shop manual to do all the tests they described on the EGR system, and it passed. Next idea?