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Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ and JK

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post #11 of (permalink) Old 06-20-2009, 06:04 AM
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How is recycling heated air into the system going to make the temp in the combustion chamber lower? Seriously? I'm no scientist, only thing I can think is it's going to dilute the air making it less combustible and in hand less efficient.
"Less efficient" might not be exactly the right term, but that's pretty much what happens. Combustion is cooler which decreases the amount of nitrogen oxides that form. Most engines since the mid-70s have had some form of EGR, My '78 has a direct passage between the intake and exhaust manifolds, and a vacuum operated valve that regulates the flow.

If the threads are stripped and otherwise boogered, and you don't anticipate ever re-installing the system, you might as well tap the holes and put in something else. I think that a 1/4" pipe tap might work. Take your tube to a hardware store and match the size of the fittings with a tap. When you do the hole in the intake, put a coat of thick grease on the tap. That will catch the chips so that that they don't wind up in the intake stream. Back it out every few turns to clean and re-apply the grease. Pipe taps are tapered, so you don't want to go too far. Turn it in a way and then test-fit the plug. You can go so far that the plug won't tighten up.

EVERYTHING's easy for the guy who doesn't have to do it.
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post #12 of (permalink) Old 06-20-2009, 08:45 AM
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Two possibles here - just warm air or actual exhaust?
A picture of the hole in the exhaust manifold and what/where those tubes were connected would sure clear things up.

When the hole on the exhaust manifold has nothing in it - is it an exhaust leak where you get exhaust blowing out? Or is it just warm air from a choke stove? It could be just a cavity in the exhaust manifold to heat up air to operate the choke.

Or, if the hole goes all the way into actual exhaust, it could be for the EGR. Yes, recycling a SMALL amount of exhaust back into the intake does lower the combustion temperatures. That's how/why EGR valves and floor jets work.
The exhaust is an inert gas, supposedly it no longer has oxygen or fuel in it - if the engine's running right. It's not unlike Helium, it does nothing but take up space. Recycled back into the intake, it spaces the HC and O2 molecules slightly apart, lowering combustion temps. But only a little bit is needed, too much radically affects performance - downward.

When the combustion temp gets lowered a little, below about 3000 degrees. 3000 degrees is about where Nitrogen gets welded to Oxygen, forming Oxides of Nitrogen (NOx,) - deadly gasses that cause smog.

Now reality - many folks just don't understand what they have, many folks modify or drill things out, thinking they are improving things. That's not always the case, but the previous owner may have.

Take a few pics of what you have, and tell us what comes out of the hole in the exhaust manifold when it's unplugged. Then we can help better.

Hopefully there is no real pressure that comes out of the hole, then it's simply a warm air "stove" to heat up the choke.

Yes, there are plugs available for flared fittings. Go somewhere they have a good assortment of fittings. Or you can just fold and pinch off the tube, or solder/braze/weld it shut.
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post #13 of (permalink) Old 06-20-2009, 09:45 PM Thread Starter
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It is exhaust that comes out that is how I knew the plug came out I suddenly had a loud as heck exhaust leak in the engine compartment.

It's not the thing you fling, It's the fling itself!
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post #14 of (permalink) Old 06-23-2009, 04:09 PM
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For what it's worth, when I used to have to put my 88 YJ up on the rolling dyno for emissions testing, she wouldn't pass without the EGR connected. My EGR valve was bad, and at the time it was a dealer-only item. IIRC, about $75.

The pulse air system, and most of the other stuff I had disconnected, but the EGR was one item I had to have or my NOx was too high.

If you have the EGR valve in place, and if it's seated properly and you don't have a vac hose to it, that should effectively seal the intake side of the pipe.

You will need to seal the exhaust side.

Good luck,

88YJ: Old, noisy, slow, and just generally wonderful. Wheeling Jeep.
04WJ: Less old, less noisy, less slow, daily driver Jeep.
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