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View Full Version : 1991 240sx: Mechanic says I need new AIV to pass emissions


grachman
04-02-2008, 06:02 PM
Anything i have read says that aiv has neglible effect on emissions?

BoostinGST
04-02-2008, 06:04 PM
i dont understand.

nastjuid
04-02-2008, 06:07 PM
The AIV (PAIR) I assume you mean. Was actually removed in the S14s because all they did was cause problems. The valve gets stuck open, and the sensor element in the MAF gets coated and you start having problems that don't diagnose a like MAF misread.

Or something along those lines. Anyway, Someone chime in here and correct me if I'm wrong, but you should be able to pop the AIV off and clean it. Might search the usual forums for a writeup on that before you go and replace it. And it's extremely easy to get to :)

Edit: er, we're talking about the box and valve that connect to the intake filter housing, just before the MAF.. right? Other end connects to the exhaust? And is this just something the mechanic said, or did you take it to get smogged and fail? It does reduce emissions, but only by a c**t hair.

grachman
04-02-2008, 06:50 PM
Yep, the PAIR valve. I took it to a mechanic and he is saying I need a new one to pass. I've already looked at it and it is beyond repair. All the studies I have seen says it has negligible effect on emissions. Pretty sure it was not working or disconnected in past years and it passed with it disconnected.

DarkPhoenix
04-02-2008, 07:19 PM
It is a part of the emissions system, and by Federal law, needs to be in place for it to be smog legal. I am pretty sure Canadian Laws mirror US emission laws in the aspect. If it was OEM Emissions, it is needed to pass the Visual Emissions.

Is it there and not connected? Or just missing altogether?

nastjuid
04-02-2008, 07:22 PM
Well if that's the case, and I'm just saying this is just what I would do, and I make no recommendation. I'd do 1/3 a bottle of seafoam via brake booster line, (feed, let sit, fire up and burn off), then do about
1/3 bottle through the gas tank on at least 9 gallons of gas, then give it a go.

The only time I actually pull the filter out and connect the PAIR to the intake box is when I have to go to get it smogged. I don't know if the valve is stuck open and I don't really care. I've passed every year, and I'm in California of all places.

Dark's right on that all the way. Leave it on for emissions, even with it stuck open, if you seafoam that mug, you should pass. If it's negligible to have it off, then it's negligible to have it on. If you were going to fail with it on, you were probably going to fail with it off, too :P

grachman
04-02-2008, 08:38 PM
I have the PAIR valve. I just know it send exhaust into my filter box. Its possilbe that I have had the PAIR valve connected for the times I have passed. There is no visual inspection in british columbia.

I have been told over and over(on the internet) that it makes almost no difference to emissions when it is disconnected.

Titan
04-02-2008, 11:01 PM
The AIV doesn't send exhaust into the airbox, it delivers air to the header in order to warm up the catalytic converter faster.

The EGR is what sends exhaust into the intake manifold.

The reason the AIV has negligable impact on emissions is because the cat is already hot when you go to test.


That being said, I removed both my AIV and EGR on my 89 sohc and I passed with flying colors in Ontario, Canada.

Hell, after I went KA-T I still passed, but not as well.

racepar1
04-02-2008, 11:05 PM
The AIV valve (the one by the airbox) has absolutely no affect at all on emissions. Mine passed clean as hell without it.

grachman
04-03-2008, 12:47 AM
Thanks for the replies. I get the new aiv on friday so i will find out.

grachman
04-03-2008, 12:43 PM
Do you guys have idle tests? I only failed the idle test. I did fine during the driving test. My province might be the only area in north america that does an idle test which would explain this discrepancy.

Dream240
04-03-2008, 02:39 PM
Thanks for the replies. I get the new aiv on friday so i will find out.

Wait, so after everyone telling you that you don't need it to pass smog you bought one anyway? WTF? Why bother coming on here and asking for advice if you're not going to take it? Sheesh......

As far as the idle test goes, certain things are checked at idle in CA, but for the rest of the continent I'm not sure.

What part of the test are you failing exactly? Which gases? hydrocarbons? The tech should have told or you should have gotten a print out. If not and you're just taking his word for it, he's ripping you off.....trust me.

In case this isn't obvious, I'm asking cause I'm trying to help you.

nastjuid
04-03-2008, 02:57 PM
AH-HA! I thought I knew this thread from somewhere, Mr. BC! *wave*

To add to my previous post, since titan pointed out that it sounded like I was saying it sends exhaust into the airbox (it doesn't), at least it's not supposed to.

The PAIR valve sends air to the exhaust manifold using a vacuum created by exhaust pulsation. When the exhaust has negative pressure, it sends air to the exhaust manifold. When the exhaust has positive pressure (above atmospheric pressure), the reed valves prevent air being sent back into the air cleaner.

The reason they aren't in the S14, is because that reed valve gets stuck, and when there's positive pressure and it's stuck open, exhaust ends up in the air cleaner.

If the iav was stuck open, i don't think it would be a big deal, since at negative pressure, the reed would be open, and at positive pressure, you'd be recycling exhaust gases just like EGR does. You might sputter a bit, but you shouldn't fail emissions just from that I wouldn't think...

In that case, I'd have to go with Dream240 on what exactly you failed on.

bo2o
04-03-2008, 02:57 PM
is canada that strict?

there a bunch of dooches. haha.
you can pass with out it if you plug it all up is more a visual part then a working part. i would say cap it off from both ends and leave it in and tell him to see what gas your failing by.

grachman
04-03-2008, 03:02 PM
Wait, so after everyone telling you that you don't need it to pass smog you bought one anyway? WTF? Why bother coming on here and asking for advice if you're not going to take it? Sheesh......

As far as the idle test goes, certain things are checked at idle in CA, but for the rest of the continent I'm not sure.

What part of the test are you failing exactly? Which gases? hydrocarbons? The tech should have told or you should have gotten a print out. If not and you're just taking his word for it, he's ripping you off.....trust me.

In case this isn't obvious, I'm asking cause I'm trying to help you.

Im failing hydrocarbons and carbon monoxide at idle. The government does the testing in Canada. I take it to mechanic to have repaired if it fails. I then go back to government for retesting. I pass automatically as long as mechanic is certified. I had the aiv completely disconnected this year when I
did the government test. Im assuming this is why I failed.

nastjuid
04-03-2008, 03:09 PM
wow, are you shitting me? so if this mechanic puts in the new IAV, and you're still failing on hydrocarbons and carbon monoxide, you still pass? Or do they not even test you again?

Dream240
04-03-2008, 03:57 PM
Im failing hydrocarbons and carbon monoxide at idle. The government does the testing in Canada. I take it to mechanic to have repaired if it fails. I then go back to government for retesting. I pass automatically as long as mechanic is certified. I had the aiv completely disconnected this year when I
did the government test. Im assuming this is why I failed.

Sounds like your running too rich. How's your timing? Also what maintenance have you done to the vehicle? Have you replaced the CAT? O2 sensor? Ran intake cleaner? Cleaned MAF? Pulled EGR and cleaned the shit out of it? Spark plugs & wires? fuel pressure test? Injectors running good?

There's tons of things that you can do first to help those pollutants. I doubt it's your PAIR, even if it's sticking, replacing it will most likely still fail emissions. Even if they aren't re-running the emissions on the 2nd time around, doing these simple maintenance items will net you better performance and MPG.

grachman
04-03-2008, 09:30 PM
wow, are you shitting me? so if this mechanic puts in the new IAV, and you're still failing on hydrocarbons and carbon monoxide, you still pass? Or do they not even test you again?

yeah, you get passed.

grachman
04-05-2008, 02:29 AM
Part was not in today. Found a source on net that says that aiv is needed for 91-93 240sx to burn off fuel spray from injectors during idle. This might explain my rich idle.

I pulled up the following from a Google search for "PAIR valve." (http://www.google.com/search?hl=en&q=%22PAIR+valve%22&btnG=Google+Search) It's pasted from an article by Dan Thompson on SE-R.net (http://www.se-r.net/header_exhaust/pair_valve.html):

> What is the PAIR?

Pulsed Air Induction Reed Valve - for all intents and purposes, it's the smog pump. Its job is to introduce fresh air into the exhaust upstream of the cat/con during deceleration and extended periods of idle to help keep the cat "lit off" (at operational temperatures). The PAIRV disappeared from the engine in '94, with Nissan citing engine improvements being responsible for no longer needing it.

The '91 thru '93 high-port engine had problems with "port wall wetting" (not to be confused with "bed wetting", though it's worse in the ARB's eyes), where the injector was far enough from the intake valve that some fuel was sprayed onto the intake port walls. When the throttle was snapped shut, the increase in port vacuum sucked this extra fuel into the combustion chamber and caused hydrocarbon emissions to skyrocket. In addition, low intake port velocity at idle also caused an increase in port wall wetting, leading to a similar condition. The PAIRV was there to introduce enough fresh air into the exhaust for the cat/con to burn off the excessive hydrocarbons.

The '94 and newer low-port engine moved the injectors closer to the intake valve and increased intake port velocity at low engine speeds. These changes were enough to allow for the elimination of the PAIRV. They were also responsible for the improvement in the engine's low-end power.

I don't think removing the PAIRV would cause any physical problems such as melting the cat/con, as it would actually cause converter temperatures to drop. Then again, it would offer no performance advantage, aside from maybe a small reduction in weight. In addition, it would increase tailpipe emissions, possibly to the point of failing a smog check. Personally, I left mine intact and functional.

Dream240
04-05-2008, 06:12 PM
You still haven't answered my questions.

And if you're so convinced that this is your problem, then why did you start this thread? I assumed that you started it to find out if we thought that the PAIR is your problem.

There could be many reasons for you running rich at idle. If you're not going to take our advice then why post? Seriously?

On a side note, I had a 91' KADE and I actually replaced the PAIR valve with a new OEM one just because the diaphragm was shot and I don't like having broken parts on my car. When I did the replacement, I completely disassembled the whole PAIR system and cleaned the shit out of it, reeds and all, and replaced the rubber hose with some vacuum line. Just to make sure I was getting the most efficiency from the system as I could. The point of this story is, the PAIR was shot for years, and I passed smog just fine, with a new CAT and O2.......

grachman
04-05-2008, 07:32 PM
You still haven't answered my questions.

And if you're so convinced that this is your problem, then why did you start this thread? I assumed that you started it to find out if we thought that the PAIR is your problem.

There could be many reasons for you running rich at idle. If you're not going to take our advice then why post? Seriously?

On a side note, I had a 91' KADE and I actually replaced the PAIR valve with a new OEM one just because the diaphragm was shot and I don't like having broken parts on my car. When I did the replacement, I completely disassembled the whole PAIR system and cleaned the shit out of it, reeds and all, and replaced the rubber hose with some vacuum line. Just to make sure I was getting the most efficiency from the system as I could. The point of this story is, the PAIR was shot for years, and I passed smog just fine, with a new CAT and O2.......


Do you have a smog idle test in California? I have written tutorials on the AIV saying it did not affect emissions. Im now thinking it does affect emissions. Even if you dont have port wall wetting , the idle on the 240sx tends to be rich so the AIV is going to help a lot of different conditions ie leaking fuel injectors. Some people can pass without it but it doesnt mean that it isnt useful for everyone. It seems that every last person posting on this subject for past few years was 100 percent wrong. And that pisses me off!!!

Z U L8R
04-06-2008, 12:43 AM
get a Datsun and don't worry about emissions ever again weeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

Dave =]

Dream240
04-07-2008, 08:19 AM
Do you have a smog idle test in California? I have written tutorials on the AIV saying it did not affect emissions. Im now thinking it does affect emissions. Even if you dont have port wall wetting , the idle on the 240sx tends to be rich so the AIV is going to help a lot of different conditions ie leaking fuel injectors. Some people can pass without it but it doesnt mean that it isnt useful for everyone. It seems that every last person posting on this subject for past few years was 100 percent wrong. And that pisses me off!!!

ugh...nevermind...you fail at answering posts. Later.

grachman
04-07-2008, 03:15 PM
re.: 1991-1993 240sx
Figured this out. You definitely need the AIV to pass aircare in British Columbia. You dont need it in California(you only need it for visual inspection) because California ECU's are different. YOu stay in closed loop during idle. ie the O2 sensor controls mixture at idle. British Columbia may be the only place in the world that needs the AIV to pass emissions. If you have an idle test and you live outside California, it is likely that you do need the AIV to pass, however.
non-california 240sx's will be rich at idle. the aiv supplies air to cat so it can burn off the extra fuel. if you measure richness at the o2 sensor you will be rich with or without the aiv.

miklos
05-18-2009, 12:01 AM
The AIV valve (the one by the airbox) has absolutely no affect at all on emissions. Mine passed clean as hell without it.How do you pass the visual without it? Did you remove the pipe from the exhaust manifold?