1991 240sx: Can you pass emissions without the PAIR (AIV) valve?

[vancouverbc]

Mechanic said I needed a new AIV to pass emissions. I've always heard it had close to zero effect on the emissions? I took the test with it totally disconnected.

[OldmanPurdy]

Mechanic said I needed a new AIV to pass emissions. I've always heard it had close to zero effect on the emissions? I took the test with it totally disconnected.

I was told the purpose of the AIV was to make the cat heat up faster similar to what the pre-cats do on modern cars, so it shouldn't make any difference once the vechicle is at operating temp. Prehaps its a visual inspection fail?

[vancouverbc]

There is no visual inspection. We do have an idle test. Maybe other areas dont have idle tests. I did fine in the driving test. Failed the idle only.

[OldmanPurdy]

Did the mechanic know it was disconnected? If so there could be another problem with the emission system causing you to fail and he's just assuming its the AIV because it wasn't working?

[vancouverbc]

Did the mechanic know it was disconnected? If so there could be another problem with the emission system causing you to fail and he's just assuming its the AIV because it wasn't working?

Yeah, that was my first impression which really pissed me off. I talked to the owner today and he was at least polite and knew something. He said the 240sx was the worst car for emissions and that some need the AIV to pass. Im thinking these guys might just be parts changers.

They did say that when they plugged the AIV in that it did get emissions under control intermittently. That might have been an illusion. I did pass last year with this AIV and then stored in my house until I put it on to take to mechanic.

[vancouverbc]

Here is somebody saying that the aiv was needed on the 91-93 models to burn fuel spray from injectors during idle.

I pulled up the following from a Google search for "PAIR valve." It's pasted from an article by Dan Thompson on SE-R.net:

> 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.

[OldmanPurdy]

Well that all makes sense I didn't know the AIV/PAIR was used after the car warmed up, either way your best bet would be to find a working PAIR or clean out the one you have. Since most S13 "modderz" ditch them even if they work you might have a good chance of getting one cheap, if not you can clean the one you have....If I recall correctly the issue with them is dirt buildup on the reed valves inside the unit that cause them to be stuck open/closed.

[vancouverbc]

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.
Modified by vancouverbc at 6:05 PM 4/8/2008

[vancouverbc]

Well that all makes sense I didn't know the AIV/PAIR was used after the car warmed up, either way your best bet would be to find a working PAIR or clean out the one you have. Since most S13 "modderz" ditch them even if they work you might have a good chance of getting one cheap, if not you can clean the one you have....If I recall correctly the issue with them is dirt buildup on the reed valves inside the unit that cause them to be stuck open/closed.

YOu are right about getting the aiv cheap. SHould be lots around. The mechanic mentioned that the plastic coating comes off the reeds and they curl after awhile. Thanks for the intelligent input.

[Rucca]

Just passed Delaware emissions with no PAIR, no EGR, PCV, swirl control.. basically I just have a cat and I passed no problem. 2 speed idle test

[vancouverbc]

Just passed Delaware emissions with no PAIR, no EGR, PCV, swirl control.. basically I just have a cat and I passed no problem. 2 speed idle test

How can an idle test have a speed? are you sure it is not a driving test at different speeds? i realize the car is stationary but the wheels are moving on rollers.