EGR system - what's it all about?

M

M Darrah

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For my own satisfaction, can someone explain, preferably with some pictures, what parts are involved in the EGR system? I have a set of very clean 2004 Cobra exhaust manifolds that I'm looking to swap for the stock manifolds sometime in the near future. There is one "bung" on the rear of the driver's side manifold for the EGR tube I assume. How does it compare to the Mark VIII manifolds? I don't have my car at the moment so I can't even compare them.

I've found a couple of pics of Cobra EGR tubes removed from the car and they have little "branch" tubes coming off them as well. What do those go to?

Basically I'm just curious how all the various tubes hook up to everything and what is different between the Cobra and Mark VIII manifolds besides the fact that the EGR hookup is in a different place. Can a good exhaust shop fabricate a custom tube to hook up the manifold to the stock EGR valve? An EGR delete is not an option, as I need to pass emission tests. I can't find a good diagram anywhere that shows how everything hooks up.
 
Maybe these will help. '98 Cobra, the later cars are similar, but I don't have those manuals on disk.
 

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Thanks Doug, that helps a lot. Now if I could find something similar for the Mark VIII. All I can find in the service manual is a cryptic diagram in a schematic format instead of a "real life" diagram like yours.
 
On this picture of your car, is that the EGR tube connected to the header? Did you fabricate it yourself or was the header a direct fit?

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Sorry for the stupid questions, but I'm trying to figure out what all the different plumbing is. For example, in your pic of the headers, I see three connectors on the driver's side and two on the pass side. I know about the O2 sensors at the rear, but what are the two things at the forward end of each header for? Are those also for O2's? I thought the system needed one set on each end of the cats.

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What it boils down to is trying to figure out what has to be done to make the Cobras fit into the car. And yes, I'll be buying a new rag joint from you. :D
 
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M Darrah said:
On this picture of your car, is that the EGR tube connected to the header? Did you fabricate it yourself or was the header a direct fit?

Sorry for the stupid questions, but I'm trying to figure out what all the different plumbing is. For example, in your pic of the headers, I see three connectors on the driver's side and two on the pass side. I know about the O2 sensors at the rear, but what are the two things at the forward end of each header for? Are those also for O2's? I thought the system needed one set on each end of the cats.

What it boils down to is trying to figure out what has to be done to make the Cobras fit into the car. And yes, I'll be buying a new rag joint from you. :D
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Yes, that's the stock '98 EGR tube.

The forward fittings are for the stock AIR system.
 
M Darrah said:
What it boils down to is trying to figure out what has to be done to make the Cobras fit into the car. And yes, I'll be buying a new rag joint from you. :D
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I think that you're going to have a problem with steering shaft clearance, even with a Flaming River joint, but I could be wrong, I've never tried it.

Also, I know for a fact that the '98 Mark VIII and '98 Cobra EGR tubes are different thread sizes where they connect to the header/manifold. So you're probably going to have to get creative.

Here's a better pic of the EGR tube connection.
 

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So I take it the Cobra doesn't use an air pump system since I can't find anything about it. The manifolds only have the EGR fitting, nothing else. Jeremi had the same manifolds on one of his cars so it can be done, but I may not have done all my homework since I didn't ask about the emissions crap.
 
Get rid of EGR and air injection, you don't NEED it and it can be tuned out. My car has the 03 manifolds, I can try and snap a few pics for you.
 
95blklsc said:
Get rid of EGR and air injection, you don't NEED it and it can be tuned out. My car has the 03 manifolds, I can try and snap a few pics for you.
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I'd love to do that, but I have to pass inspection here. If they hook up to the computer, won't they be able to tell if it's been altered to eliminate the EGR and air systems? What the heck did Cobras use in place of air injection anyway? If this turns out to be more trouble than it's worth, I'll probably be posting up a very clean set of manifolds for sale. Headers are not an option.
 
You could probably connect the plumbing but the Mark VIII gets the EGR exhaust gasses from a fitting in the cat. I'm not sure if that would make a difference.

I don't have photos but here are some basics, as I understand them, that might help.

The EGR tube carries exhaust gasses and puts them back into the intake (only when conditions are right) to lower combustion temps, decrease emissions, increase fuel mileage, and filthy up the IMRC plates.:D

There is an orifice in the EGR tube, and on either side of that are the 2 little tubes you see.

Those tubes go to the DPFE sensor (Differential bla bla) which measures the difference of pressure before and after the orifice.

This data from the DPFE goes to the PCM to control the EGR valve.:)
 
M Darrah said:
I'd love to do that, but I have to pass inspection here. If they hook up to the computer, won't they be able to tell if it's been altered to eliminate the EGR and air systems?
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Do they hook up to the PCM now? If they do it's likely only to see if it has any codes. The tune or chip will not show any such codes.

I think you need to do more homework.

Chances are they only check the PCM for codes and do a 'sniffer' test. A well tuned car will pass with flying colors with no EGR or AIR system. The EGR can be made to work in case there is a visual test but they will probably never notice the deletion of the AIR system.
 
driller said:
Do they hook up to the PCM now? If they do it's likely only to see if it has any codes. The tune or chip will not show any such codes.

I think you need to do more homework.

Chances are they only check the PCM for codes and do a 'sniffer' test. A well tuned car will pass with flying colors with no EGR or AIR system. The EGR can be made to work in case there is a visual test but they will probably never notice the deletion of the AIR system.
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Many states, just recently NJ for one, now check the PCM for completion of the OBDII readiness test. If you have disabled some systems, then the test cannot complete, and your car fails. :(

And, by the way, the AIR system is one of the tests conducted by PCM OBDII readiness test, I had to turn mine back on in my Cobra to pass.
 
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Illinois doesn't do a sniffer test, at least not up front. They plug into the computer it's either pass or fail. After doing a little more research, it looks like they do perform readiness tests as Doug described.

I'd always intended to keep the EGR intact, and since the manifolds have the fitting, I figured it would just be a matter of fabricating a proper tube. What I didn't count on was the air injection system, which was the missing piece of the puzzle when it came to plumbing I recalled seeing. There's nothing on the Cobra manifolds for that. I seem to recall reading somewhere that 03 > Cobras don't use an air pump system. (?)
 
There may be a way to trick the PCM into not detecting a system has been disabled. I know someone who is able to disguise that the cats and O2 sensors are missing from his mustang Gt with a very minor electrical modification. Without the modification there are immediate engine codes. This person passes Illinois immisions with flying colors on the computer check. Obviously a sniff test may be different.
 
DLF said:
Many states, just recently NJ for one, now check the PCM for completion of the OBDII readiness test. If you have disabled some systems, then the test cannot complete, and your car fails. :(

And, by the way, the AIR system is one of the tests conducted by PCM OBDII readiness test, I had to turn mine back on in my Cobra to pass.
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MA does the same OBD2 plug in test. My 97 passes just fine with the tune, all of these parameters simply turned off.
 
I'm sure if you do some searching on a mustang or corvette forum in the tuning area you will find someone from you state that has first hand experience with this.
 
You could have a machine shop drill and tap the new manifolds with the correct thread size, and then swap the fittings over.
 
I finally got around to doing some more research on emission tests and found a couple of Chicago-area Mustang forums. Everyone says that you'll pass as long as you have the car custom-tuned to disable the various systems. One guy had EGR, O2, AIR, and even EVAP all saying "not supported" on his emission report and he passed just fine lol.

Now to figure out what to eliminate... EGR and AIR must go for sure.
 
Why do you want to delete the EGR?

I think the advantages far outweigh the disadvantages.
 
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