Air Injection Delete: AKA Those Ugly Steel Exhaust Tubes

Name: Mark (Zanzer)
Location: Newton, North Carolina
Vehicle: 1986 Mazda B2000 Extra Cab




How To Delete Air Injection Lines: Or as many call it "Those ugly steel tubes on the exhaust manifold"


Since I've received a few PM's about this modification on my truck I thought I'd do a small write-up on how it's done.


When I first bought my truck the previous owner had tried to delete a lot of the emissions equipment under the hood and really hacked up the air injection lines that run from the exhaust manifold and catalytic converter to the reed valves on the air cleaner. My truck also had a very bad smoking issue and since these pipes were now leaking at many different points I now had a problem with large amounts of smoke coming from under the hood. Like many of us, he had also tried the old "cut off and crimp the end" trick but it still smoked a little, leaked a little oil, and just looked horrible in general.



One day I decided it was time for all this mess to go since it wasn't doing anything short of taking up space and looking terrible.


I first stared by trying to find something to plug the ports on the exhaust manifold. After some trial and error I found the thread pitch on the ports to be M14 - 1.50 and as luck would have it there's also a Honda oil drain plug available in that same thread size. I went to the local AutoZone and picked up 4 of these plugs. They didn't have 4 of the same part number so I had to split up into 2 and 2 of different numbers. 2 were Needa Part PN 652946, I don't remember the part number of the others and have since lost the packaging, but the important thing here is to purchase the shortest ones they have.

The ports aren't tapped very deep so shorter plugs work better and in some cases you may need to install a large washer (as can be seen on 2 of mine) or just keep running the plug in slowly and allow it to cut some new threads. The plugs are VERY close to the needed depth so it shouldn't take much. If the plugs you purchase bottom out early and still have a lot of visible space between the manifold and bolt head I suggest installing a washer to make up for the difference.



For the tube that connects to the catalytic converter:

All I did here was make a block-off plate. I used a piece of 3/16" thick steel plate that was close to the width of the mounting flange and cut it to length. I then used the factory metal gasket between the tube and flange as a template for size and spacing of the holes that needed too be drilled in the block off plate. After drilling the holes I painted it black to match and installed it using the factory steel gasket between the plate and flange.


Everything looked good enough to pass a visual inspection and so far the smog police haven't given me any hassle over the mod since it's fairly clean and simple. I'd think they'd be more inclined to give someone a hard time over tubes that have been cut off and crimped, but plugs and plates look a little more "factory" and don't seem to draw much attention.



Onto the pics


Here's the mess as delivered. The previous owner had bent the tubes to the reed valves so I had a hard time keeping those connected and it's hard to see in the pics but the main line from the exhaust manifold has the standard "cut off and crimp" at the end of it.

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Here it is after removing the lines and installing the plugs.

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As you can see in this pic. I had to install washers with these 2 plugs. Luckily they came with the plugs

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Here's a shot after a couple of months of service. Everything has the "new" burned off and blends in pretty well. You'll also notice the heat shield is gone. That's because I had an exhaust leak and since I'm a tightwad I went with the 626/MX-6 gasket ($7) instead of the B truck gasket ($20)

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Here's a couple of pics of the block-off plate installed. I thought about doing 45's or a radius on the ends of the plate to make it match the flange better, but it still looks way better than the factory tube. This is all temporary on this truck anyway.

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And finally a shot of everything together. You can see the block-off plate in the bottom center of the pic just to the lower left of the cat.

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