Help - failed smog test - Nox too high

[87mk1gold]

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]

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]

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]

I always wondered how seafoam worked.

[tstoney82]

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

[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.

[tstoney82]

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]

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]

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?

[Tin_le004]

bump

[bassman54]

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.

i've used it with good results as well. i did not get a check engine light.

the thing is, in cali, no smog check , no registration, and if seafoam gets you to pass smog it's a good use for it.

to recap, as tstoney82 stated above, seafoam is a good fix for carbon build up inside the cilynders. this causes elevated combustion temperatures, which increases nox. egr is used for this reason, because it lowers combustion temps.

again, this is from experience, not theory.

[marazaii]

bump for ppl with carbon build-up.

[David]

Originally Posted by Tin_le004

bump

What was the point?

[marazaii]

^

[Mr2Trey]

I had this problem, swapped my O2 sensors, and it passed just fine.

[Tin_le004]

Originally Posted by David

What was the point?

I currently have NOx problem, wanted to refresh the post again for some idea on how to fix it...since last time anythin was said was in 09.. .. Bump ^^

[Bigbacon]

we just went through this pretty much about 10 threads down on page one.

Smog Check Fail

sister thread at the other forum

MR2 Owners Club Message Board

confirm your timing, confirm your O2 sensor works, confirm your ERG works. Probably have to replace your CAT as well.

[David]

I do have a perfect fix. You don't even have to pick up a wrench or get your hands dirty.



























Move to a state that isn't california.

[dirocyn]

I'd have to pick up all my wrenches to move, though!

Nox emissions usually mean the EGR isn't working. Make sure the vac hose to the EGR valve actually gets vacuum--it could be a hose loose or clogged, or a VSV not opening. Get out the Mity-vac to make sure the EGR valve will move if you apply vacuum. If this doesn't fix it, try Seafoam through the manifold and then replace the spark plugs with new plugs in the proper heat range, with the right gap setting.

[Zarek]

check your EGR modulator. Its that round brown thing on the driver side of your engine. Disconnect it from the hoses and open it up. if the thig is really dirty try cleaning it by blowing it out gently, or replace it. I replaced mine for 25 bucks.