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Unread 11-14-2013, 04:39 PM   #1
SouthernGypsy
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EGR vs Gas Miledge vs Power on I6 CJ-7

I need to know how having or not having the EGR valve affects MPG's and Power?

I realized today that the EGR valve is not working on one of our 1983 CJ-7's with the 4.2L engine and am debating if I should replace the expensive EGR valve or just use a block off plate kit which is a fraction of the price. We are in a state that has no inspections (and most of the emissions, certainly everything connected to the computer are already gone) and I want the best possible MPG's and power.

The CJ has already had the computer and all the other computer-related emissions removed. There is still a vacuum line going to the EGR valve from the CTO/EGR/Canister vacuum port on the front of the intake manifold. A line comes from the base of the carb, thru a T and then one side of the T goes to the vacuum canister, and the other to the inner (one closest to manifold) of the two ports on the port, then a line from the outer most one direct to the EGR valve. Which is already different than some diagrams which show it coming from the CTO valve to the air cleaner housing and then down to the EGR. My vacuum advance line also comes off of the line between the carb and CTO via a second T splitter. Some diagrams also show the line to the vacuum canister T'ing off after the CTO port between it and the EGO valve instead of between the carb and the CTO valve.

Mine basically looks the most like this image I found online, but that's certainly different than all the stock diagrams, and even different from many of the "post-computer/emissions removal" diagrams, with these changes;

1. My line from the vacuum advance goes to the line between the carb base and CTO switch.
2. My PVC valve is at the rear instead of the front and the line goes to a T one side of which goes to the rear of the carb at the base, and the other goes over to the canister.
3. My breather is at the front instead of the rear and has no line to it, it's a simple stainless breather cap that has no place to connect a line to it.
4. The blue line from the back of the canister connects via a T into the line between the carb and the CTO.

Other than those changes this would look like my setup;

mc2100_2port.jpg

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Unread 11-14-2013, 04:56 PM   #2
SouthernGypsy
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Not sure if my last explanation made total sense so I took a picture and added labels;
img_0015.jpg  
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Unread 11-14-2013, 09:03 PM   #3
supersport126
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I would block it off and plug the vacuum line since everything is just about disconnected anyway but really thats a lie. I would start from scratch 100% and re plumb everything. its cheep and you'll learn whats what.
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Unread 11-14-2013, 09:39 PM   #4
SouthernGypsy
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This IS the re-plumed version ~ Hahaha

The first problem is the decision about buying a replacement EGR valve or just getting a block off kit. Anyone know what the EGR does to Gas Mileage and Power/Performance? I know it supposedly reduces the combustion chamber temps (though no one ever says how much it really amounts to) but a the cost of more carbon build up over time within the intake manifold and around the valves, but never hear anything about what it does to gas miledge and power/performance?
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Unread 11-14-2013, 09:44 PM   #5
SouthernGypsy
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Actually how does the CTO even work? Is it temperature activated? Many diagrams show 4 port ones but mine only has 2.

My assumption from experience with similar things (though could be wrong in this instance) is that it has no vacuum without the line from the carb (ie. it's not open into the intake manifold itself) and that it's normally closed between the two ports but when it gets hot enough the opening between the two ports opens up allowing the vacuum to pass through. Is that correct or am I off base?

One of my concerns other than the EGR question is that I notice they have the purge signal line connected with a T between the base of the carb and the CTO switch, but if I am thinking correctly that means the canister is constantly being signaled to purge. Shouldn't that T come off between the outer port of the CTO and the EGR valve, so that the canister is only signaled to purge AFTER the engine is warm enough??
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Unread 11-14-2013, 10:48 PM   #6
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The EGR valve predates the electronic emissions controls. It is there to reduce nitrogen oxide emissions by lowering the combustion temperatures, nitrogen oxide forming at high temperatures. It does this by recirculating inert exhaut gases (no fuel or oxygen) to replace part of the fuel/air mix (5 to 15%).

The CTO valve is there because of poor running when cold with the EGR valve. Hence it only comes into operation once the engine warms up and the CTO valve opens.

The CTO valve then supplies manifold vacuum to the EGR valve. When you take your foot off the throttle the manifold vacumm increases, the EGR valve opens, the temperature of combustion decreases. When you put your foot down the manifold vaccumm drops, valve closes, pure fuel/air mix for power.

There is a small drop in effciency on a trailing throttle but you the maximum power and torque is unaffected and the engine runs cooler. It also cools the exhaust valves which last longer.

If yours is not working it might be gummed up by carbon. It is possible to take them off and clean them.

If broke and you don't want the expense or rate emissions that high then just leave it. No blanking plate is required.
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Unread 11-14-2013, 10:58 PM   #7
SouthernGypsy
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Thanks!

Am I correct when I think that the Canister Purge Signal hose should be on the same (only when warm) side of the CTO as the EGR is, and not between the manifold vacuum source and the CTO valve where it is getting vacuum even when the engine is cold? ...or is it OK that it's connected where it's getting signal even when the engine is cold?
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Unread 11-14-2013, 11:45 PM   #8
BagusJeep
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I should add that the I6 runs fine for mileage and power without the EGR valve. If you fit tubular headers you have to blank off the connection.

The main effects are that the nitrogen oxide emissions will increase, engine temperature will increase and the exhaust valve life will be shortened.

I am just glad when it starts and gets there without anything dropping off.
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Unread 11-15-2013, 04:00 AM   #9
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The EGR should come off the ported vacuum as much as I can remember. Via the CTO and the temp switch in the air cleaner housing.

Unless the diaphragm is broken in the EGR valve its probably ok.

I hooked Grammys back up to help with detonation. And I took it apart and decarboned it. I think I had three parts when I was done.

With the carb on the intake washing the intake and runners with fuel it will not get dirty from EGR.
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