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Jeep 4.0L Cold Air Cowl Vent Intake

Author: macb


I had seen several different types of snorkels, liked several of them (the Michigan Jeeper Hummer style being my favorite except for the $300+ price tag) I also liked K9's snorkel but I don't see water over the hood hardly ever...so being the cheap jeeper that I am (and the wife's new practice of hiding the visa card) I decided what I wanted to do based on these simple ideas.

my finished iintakeAnd I saw a write up on the web somewhere during my travels but there were no pictures (danged computers), so it was time to put on my engineering hat and figure this out. If you ARE going to be fording water over 4' deep then I suggest taking a look at K9's write-up concerning his very cool home built snorkel.

My jeep is drawing air from the cowl vent in front of the windshield. If I don't show it to you, you'd never know it was there. It's waterproof as long as I don't completely submerge the jeep up to the windshield (not very likely in San Antonio).

What you need:

Buy or 'obtain' the following:

Tools list:

The steps:

rivet the end pieceFirst remove the factory air box and air tube. Give the factory air box a good cleaning (unless your purchase of an air tube came with an air box also) and we will modify this first so the RTV can dry. Carefully cut a 6 inch by 5 inch piece of sheet metal and then trim it so that if fits the end of the box to cover the old intake hole where the air horn was located. (safety first, where your gloves and glasses when working, you only get 2 eyes and sheet metal is sharp!)

Test fit this onto the air box and if it looks good file the edges, give it a good layer of silicone of make it air tight and put it in place. Drill 8 to 10 holes and rivet the cover in place (I put 5 around the outer edge and then another 4 very close to the old air horn hole, then silicone over the rivets. Now set this aside so the RTV can set up.

RTVDetermine the location for the new intake hole on the engine side of the air box (under the exit tube hole in the top half of the box), by placing the one of the electrical box connector nuts INSIDE the box It needs to have clearance for the air filter, fittings, clamps when it is mounted. Be very sure to check for alternator clearance as well! Measure it twice, cut once. Drill the hole for the new intake using the hole cutter (keep the center scrap piece for later). You may have to trim the threaded end of the connector to allow for a tight fit. I took ½ inch off of mine with a hack saw. Trim the excess to allow for a smooth physical connection. RTV the nut and the connector where they will contact the box and then assemble and set aside to allow for the RTV to set up.

wiper removalRemove the cowl from the vehicle. First remove the wiper blades by folding them away from the windshield. Pull the locking tabs from under the wiper blades. Pull the blade assembly straight away.

cowlRemove the 4 screws along the top of the cowl, remove the 1 screw in the cowl vent.


remove the 2 screws at each end of the firewallLift the hood, pull the rubber seal from top edge of the firewall, and remove the 2 cowl screws at each end of the firewall.

Put the hood back down and carefully lift the leading edge of the cowl, then pull the cowl clear. Notice the large drain under the center of the cowl, this is where the water drains when it enters the cowl, on the passenger side you will also see the fresh air intake for you have an a/c unit.

Using the scrap plastic cut from the air box as a guide determine where you will be cutting the hole in the firewall for the air intake (now it gets FUN!) you want to be just left from the grounding screw in the firewall as you look at the screw head in the engine compartment and low enough to allow for clearance below the lip of the firewall and the ground screw. Also check inside the cowl for clearance of the electrical box connector nut (again you may have to trim back the length of the threaded end to allow for a tight fit when installing this connector). This is also a good time to create a little space by removing the wire loom clamps that hold the wiring harness in place (and in your way) and then releasing the connectors in the center of the firewall and relocating them under the metal ledge (be careful to not damage the connectors).

cut a hole in the firewallMeasure it again and check for clearance again, you only get one shot at this one! now it is time to drill - no turning back!!!! Make your hole in the firewall, clean up the edges with a file, mask it and give it a couple coats of paint or primer to stop any rusting. Make sure you allow the primer to dry...this is why I used the quick drying spray type (watch your overspray and remember it sprays through the hole!). Test fit the connector and then RTV all the connection points and assemble.

Holy Crap! You just made a 2.5" hole in your firewall!!! Take a break and let your heart rate come back down!

Re-install the lower half of the air box

Let's prepare the new intake tube. Cut off about ½ inch to either side of the oil breather connection - there is a base where it joins the tube - I cut mine right at the ridge of that joint. Using the metal joint sleeve temporarily reassemble the now shorter tube and check for fit and clearance in the engine compartment. If you need to trim the air tubes for length and/or fit now is the time to do it. Disassemble the new tube and RTV the interior of the metal plumbing joint sleeve (remember to remove the rubber insert). RTV the inside edge of one of the tube halves. Use the joint sleeve to tightly join the 2 halves. Back together. I put mine back at the same angles by using the seam in the tube. Put the new tube aside and allow the RTV to set up.

air tube comparison locking collar detail

Really take a break now to ensure all the RTV has set up before you begin making the mechanical connections.

installed tube in air boxAssemble the new short tube between the 2 new connectors you installed and tighten the band clamps. I found it helpful to remove the clamp keys to allow me to spin the clamps to more accessible positions. Assemble the filter and top of the air box. Assemble the air box to throttle body tube. Reverse the cowl removal procedures.

Double check all your clearances and do a tool check.

Did you remember to take PICS?

Final thoughts and testing...
1. I have run a garden hose full blast at the cowl vent with the engine running - no problem ... as long as the lower end of the vent is not blocked it will drain water super fast.
2. I might test an air scoop/air dam to see if it will affect highway performance. but on the trail I want all that cooler air going down the intake.
3. I would have mounted the connector closer to rear corner of the box
4. the size of all the tubing is just under 2.5 inches...considering that the stock air horn is only like 1.5 inches inner diameter I figured this is good.

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