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Exhaust question

K2fender

NAXJA Forum User
Location
United States
Okay, so my exhaust broke off at the cat on my 85 XJ. I am going to put the exhaust on from an 88 fuel injected cherokee. On the 85's exhaust there is a line running from the cat and also from the downpipe to a cylinder in the engine, which in turn has a line running from it to the carb. The 88's exhaust does not have this. Will I be okay without those two lines going to the cylinder, and just plugging the holes in the cylinder instead? From what I have heard, one of the lines just takes any gas from the engine that gets down to the cat and brings it back up to the cylinder and in turn to the carb. Thanks.
 
If I'm not mistaken those lines are designed to supply a little extra air to help the converter convert.
Depends on what type and how strict your inspection and smog test is. The late model catalytic converters are said to do the job, better than the old style or so I've heard (In advertisements from the people who own the patent on the new style).
 
8Mud is correct -- those two lines are part of an air injection system. I am not sure about what "cylinder" you are referring to but the system takes air from a hose attached to the top of the air cleaner. From there the hose goes to a couple of metering valves (probably the cylinders you are referring to) which also serve to pulse the air, using vacuum, and inject it into the downpipe and cat.

Depending on your emissions testing situation, that whole mess including the valves/cylinders and hoses can be removed which will leave room under the hood to actually do some things like changing the oil filter and getting at the distributor. You can just plug the vacuum lines and be sure to properly plug the hole in the top of the air cleaner.

On a side note, it is of course illegal to remove any portion of the emission system. A professional mechanic moonlighting out of his home did some work for me years ago and took the lines off of the cat and pipe. I finally removed the mess under the hood. I don't know what effect this has on emissions but I seriously question whether any of this stuff is working as an efficient, coordinated emission system in these 20 year old carbed trucks to start with. And I don't know where one would go to find out other than perhaps spending a fortune at a dealer shop.
 
Pelican said:
I don't know what effect this has on emissions but I seriously question whether any of this stuff is working as an efficient, coordinated emission system in these 20 year old carbed trucks to start with. And I don't know where one would go to find out other than perhaps spending a fortune at a dealer shop.

Being a GM guy, I've fooled around with these systems quite a bit (GM typically put AIR systems on everything, and they still do). The extra air injected into the exhaust stream isn't supposed to "thin out" the exhaust gases, as one might expect; it actually aids in the burning of unburnt hydrocarbons within the catalytic converter... the R in AIR stands for "reaction." It's primarily used during cold engine operation and sometimes under other load situations.

With regard to emissions, it probably results in a slightly dirtier exhaust on the smog test. Of course, if your county/state does a visual inspection, the vehicle will fail if the AIR system isn't there -- even if the tailpipe is as clean as before.
 
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