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What is this plastic box on the air cleaner intake for?

1997 Nissan PU, 4x4, king cab, XE. There is a large plastic box thing just inside the engine compartment that is bolted to the fender housing on the driver's side. The air coming from outside the vehicle has to pass through this box before it continues on to the air cleaner housing. I've been wondering about this box for the 7 years I've owned the truck, but always forgot to ask.

The outside air comes through a 3" plastic moulded tube from inside the wheel well. The tube then splits into a "Y" configuration, with a 3" tube going into the upper portion of the box, and a 2" tube going into the lower portion of the box. On the other side of the box, there is a

3" tube that goes to the air cleaner. I have taken this box out and it is completely empty. There are no electrical connectors, nor sensors, nor any holes in the case for outside air.

When I say "a box", I mean the whole unit, since it is two separate compartments that are riveted together. The upper compartment is where the air passes through between the fender and the air cleaner housing. The lower compartment does not appear to have any purpose whatsoever. It is not open to the upper box and has only one outlet which accepts the lower 2" tube of the "Y" configuration mentioned above. Basically, it is a dead end for air. This box must have been very important for Nissan to have included it, since they provided 3 bolt-on brackets to mount it to the body, and had to design the extra moulded tube fitting between the air source and the air cleaner. The only thing that I see as the use for this 'box' is to confuse the air, or break up the air flow, so it is not a direct run from the fender to the air cleaner, but that doesn't make sense. The box certainly does not confuse the rodents. They apparently can find their way though the tube from the fender to the air cleaner housing without any problem.

Reply to
Bill Schnakenberg
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It's for noise suppression.

Reply to
Steve T

Thanks, Steve, I respect your expertise, so on that basis, I removed the box and ran the truck for a test drive. I live in the outback of NYS, so the main roads are all 55 MPH, where I could wind it out. Without the box, I could not discern 1 decibel of difference in noise than with the box. It's 77 f. degrees out so I had the windows open. I came back home and then took the crossover tube off the air cleaner housing and took another test drive. This time there was a noticable difference without the cross over tube. There was a loud sort of humming sound coming from the engine when accelerating, like that which we got when we used to invert the round air cleaner covers on the old 50's american cars, so the air entered the housing all around, rather than just through the air housing's horn. I think I'll keep it this way for awhile. It sounds much more like a truck should. I wanted to put a throatier exhaust system on it anyway, which would have made it a little louder. Speaking of which... any ideas on an exhaust system that would work on a

97 2.4 4x4 king PU?
Reply to
Bill Schnakenberg

It probably only "works" at a certain RPM to cancel some weird harmonics. Many people would never notice the difference and depending on the road/tire noise your truck has, you might not either. Just the wind noise from the window down would be enough not to hear it! :-)

Reply to
Steve T

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