t88itsagpthing

I replaced the factory air system with the K&N air filter system. As you can see in the photo the air filter isn't completely inclosed so it's sucking in hot air which has caused the MPG's to drop. I'm considering attaching plastic to the existing one to close it in. Has anyone else run into this and if so what did you do any ideas welcomed.

BlueRidgeMark

Just do the sensible thing. Ditch the K&N and go back to the stock system.

t88itsagpthing

I'm thinking the same thing but then I'm stuck with the kit, I guess I can sell it.

fb97xj1

Agreed. I ran a K&N in my Mustang for a couple years and went back to paper. The only benefit with the K&N was its reuseability. Performance wise, it was a waste of my money. It did absolutely nothing, except lighten my wallet. But if you are dead set on running one, just buy a factory box and filter that fits. If need be you can modify the box and run a tube from it to the inner fender where the air is cooler.

t88itsagpthing

The original air box had an opening facing the front grill so that it was able to get cooler air into the box so it looks like I may revert back to it.

EZEARL

Or do this:

BlueRidgeMark

Given how hot the hood gets, I'm not sure a cowl intake is a huge improvement.

t88itsagpthing

That's a good idea, I need to get the factory air box since I threw mine out thinking I wouldn't need it.

EZEARL

I agree but I also believe there's no way to get a source of cold air to the throttle body. Once the air outside of the engine bay enters it it's a long way to the throttle body through a very hot area. Maybe insulating the under hood duct work? On you tube I saw an XJ with an air intake directly from the t/b through the hood above it. Don't know how he filtered it though. lol I did have a K&N set up for a good while but removed it due to rough idle issues. Cleaned the t/b and went back to OEM one and all was good. Was told the K&N oil may have been contaminating sensors?
I did the cowl mod above because rodents kept chewing through the screening at the OEM air box intake. Determined buggers for sure.

fb97xj1

The oil can contaminate sensors. MAF (mass air flow) sensors in particular as they are just after the filter. Too much oil and it coats the sensors heating filament and throw codes. Cleaning the filament should fix that. But they are delicate, and if damaged, the sensor needs replaced. So care must be taken using a K&N with MAF equipped engines. But the XJ doesnt use MAF so thats not an issue. The TPS and IAC should be safe as they dont use any exposed filaments. The MAP mounted to the throttle body should be fine as well as the port isnt in direct line with the incoming air. A majority of the oil would most likely stick to the inside of the air tube as the bend at the throttle body is rather sharp. What does get to the throttle body shouldnt be a concern. Unless you drown the filter and throw it in dripping wet.

Thats another reason i ditched my K&N. They get dirty way faster than a traditional paper filter. Its the oil. The oil is what makes it work, but its a two way street.

EZEARL

THANKS for the explanation. I've used K&N's on other vehicles so I'm sure there wasn't too much oil. Whatever was causing the rougher than usual idle removing that did the trick. Temperamental these XJ's can be.

BlueRidgeMark

Well, like a good woman, there is the maintenance to consider....

t88itsagpthing

My thought on the air heating up is that it's flowing in fast enough that it doesn't have time to heat up, kind of similar to when you run your finger through the flame of a candle.

EZEARL

And I've been very lucky on both counts. lol

EZEARL

Guess the air might be cooler when drawn in from the outside instead of from directly under the hood.
Are you aware of the available opening directly in front of the one in front of the OEM air box? There's a rectangular plate held on by screw. Remove it and you get access to air outside the engine bay. The opening is at least as large if not a bit larger than the air box opening. Before I did the cowl mod I connected the two openings using a piece of rectangular heater duct.