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air box to header tube

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Thats a good point. I just see it as, it was put there for a reason by AMC and i like to get things to how its made to be.


The way it came from the factory was a poor way to do it. Cheap hose, iffy result. Every one I've seen has either been torn off, fallen off or is falling apart. Please note that they're not even there on later models of MJ's & XJ's.


It also limits the exhaust manifolds available since a replacement with the correct O2 and EGR bungs has the funky aluminum shield on it, unless you buy custom headers for $$$.


Anyhoo, mine are gone with no apparent problems

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That hose is there to bring warm air up from by the header while the engine is warming up. If you look inside the air box intake there is a butterfly valve in there that closes when its cold to bring air in through that hole, and it opens when the engine is warm to draw in colder air from behind the front grill. Without a hose leading to the air box, the butterfly valve won't open and air will not be drawn in from behind the grill, this creates an intake restriction that can in theory hinder engine performance.

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  • 1 year later...

My son's 90 XJ came up as a "gross polluter" on the sniffer test due to a faulty O2 sensor.  When it comes up as a gross polluter the smog police send you to a Gold Shield smog station and they look at everything with a much more critical eye.  Anything not stock is flagged.  They insisted that the hose needed to be there for the "electrostatically controlled intake". 


The smog guy charged him $3.00 for the hose and put it in for free (it takes 5 seconds to put it in).  So he did the rest of the inspection/testing and passed it.  Then he told him he could take the hose out whenever he wanted.  Said it's not something you'd fail a regular test for.  Just the Gross Polluter.  In other words the hose doesn't actually MATTER...it's stock though and they have to see it in there...and of course...it's California.

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That hose is a simple throwback to carbureted days. On anyvfuel injected it is not needed.

The idea was as prevoiusly mentioned ... to assist with cold weather warm ups. Any manifold can be coverted as its just a can added to create heat 'stove' a correctly sized section of exhaust pipe withba hose clamp can replace the current fitting to convert any manifold. Should you desire to do so.


Otherwise it jusy funnels warn air up to the air box on cold days ... it is a vacuum motor valve that is thermally controlled (a thermal valve decides the function and engine vacuum does the work). It has absolutely NOTHING to do with emissions. Its just there to spped warm ups. As fo how the motor will function .... fuel, idle and timing are all ecu controlled ... the original intent was to help prevent carburetor freezes in cold climates. These are not a problem with the 4.0 ... especially in the southern states. Mine is removed and the section cut out. Underhood temps will keep the valve open and it will only be restrictive during cold start ... andbat that time it will draw air from the stove nipple ... so there is no restrictions there either.

In Canada no one cares about it since we all know what it is already.

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As Rockfrog stated, the hose is there to feed heat into the intake to help with cold starts. When it's cold enough for it to make a noticeable difference with a fuel injected vehicle, it's also cold enough that any heat will be lost by the thin, poorly insulated pipe.

My MJ no has silly tube, and I've never had any cold-related issues starting. And unlike Rockfrog's left-coast cool, it's actually cold where I live.


I would argue though that it would have a small emissions-related function. It's intended to help reduce the amount of unburnt fuel in the exhaust, and help things warm up faster, which in turn leads to better catalytic converter function. But just cause that's what it's intended to do doesn't mean it does it very well...

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  • 7 years later...
2 hours ago, Rotten Ralphy said:

If I remove the tube, do I need to do anything else (remove vacuum line, cap the header hole, etc)? 


Just remove the vacuum line and cap it off at the source.  You don't need to do anything to the valve, since it's normally closed.

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