EGR Delete and spacer

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PeteG41

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Slowly going through my new stang, 351 2v, and figuring out what I need to repair/replace/remove. I was told the EGR spacer is notorious for being burned through in a different post in this forum. Did some googling and for the life of me can't find a replacement spacer to get rid of it. I don't need to deal with the hassle of emissions so I was also going to get rid of the EGR. I read that a 351c fuel pump block off plate works to cover up the EGR being removed, however I am not sure if that applies to earlier year mustangs. If that spacer is burned through what are my options? Would rather not have to shell out for a new intake at this point, since I am still trying to get the girl to run correctly.
 
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PeteG41

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Edelbrock sells a block off plate:
For the sake of sounding dumb since that says choke block off, that plate also works to block off the EGR? This is what I was looking at to get rid of it.

 

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30 buxx for a block-off plate that you can make in no time... Amazing.
I was looking for the EGR one, not the choke. Thought about just cutting one out of an aluminum can but wasnt sure if that would work.
 
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PeteG41

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This one is a dummy block off plate that you can bolt the EGR valve to look 'legal'.

I've cut them out of 1/8" steel plate. If you want to go aluminum, I would make it at least 1/4" thick.

You can also cut out one that will completely replace the EGR plate.
Yep I actually came across that one as well, but seeing as I have a 2v, I would have to swap out a decent amount. I don't need to worry about looking legal luckily, so was going to do away with it all together. As far as cutting a plate it seems like the easiest option, and just trace a gasket, I just have no way to cut one. I bet I could call up a fab shop and they could crank one out for me.
 
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The EGR valves on the 73 Mustangs were actually not all that adversely impactful. If yours is not leaking and causing a rough idle you do not need to block it off to disable it. You can just unplug the Port Vacuum Line that plugs into the EGR Diaphragm. But, be sure to plug that Ported Vacuum line with something, otherwise the Port Vacuum line that feeds both the dual diaphragm Transmission Vacuum Modulator and the Distributor Vacuum Advance Diaphragm will lose the vacuum pressure they need to operate correctly.

For what it is worth, I have left our EGR Valve functional on our 1973 Mustang Convertible with its 302 2v engine. I had previously unplugged its Port Vacuum Line, and plugged the line, and did not notice any appreciable difference in performance. I did test with a vacuum test pump to make certain the EGR valve is working, and it is functional. I figure if I can't tell the difference in performance it was not worth disconnecting it. On some cars a functioning EGR valve is definitely causing a noticeable stumble or hesitation when coming off idle, or rough low speed engine performance. If you are not suffering from those kinds of problems it does not make a lot of sense to disable it. As bad as it sounds, recirculating exhaust gas into the intake manifold is only sending inert gas into the combustion chambers to try to reduce combustion temperatures, and decrease NOx emissions. I know a lot of folks do disable them, and in some cases they notice a performance difference. YMMV.

Attached are some 1971 - 1973 engine vacuum schematics. I am betting one of them is showing your engine calibration. You will have to dig through the PDF files to find your particular engine.
 

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  • _1967-1972_Mustang_EmissionControlVacuumSchematics_ConsolidatedGroupedAndSortedByYear__20211003.pdf
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  • 1973Mustang_VolumeVI_EmissionControlSystems_Chapter6_20210210.pdf
    5.2 MB · Views: 10

PeteG41

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The EGR valves on the 73 Mustangs were actually not all that adversely impactful. If yours is not leaking and causing a rough idle you do not need to block it off to disable it. You can just unplug the Port Vacuum Line that plugs into the EGR Diaphragm. But, be sure to plug that Ported Vacuum line with something, otherwise the Port Vacuum line that feeds both the dual diaphragm Transmission Vacuum Modulator and the Distributor Vacuum Advance Diaphragm will lose the vacuum pressure they need to operate correctly.

For what it is worth, I have left our EGR Valve functional on our 1973 Mustang Convertible with its 302 2v engine. I had previously unplugged its Port Vacuum Line, and plugged the line, and did not notice any appreciable difference in performance. I did test with a vacuum test pump to make certain the EGR valve is working, and it is functional. I figure if I can't tell the difference in performance it was not worth disconnecting it. On some cars a functioning EGR valve is definitely causing a noticeable stumble or hesitation when coming off idle, or rough low speed engine performance. If you are not suffering from those kinds of problems it does not make a lot of sense to disable it. As bad as it sounds, recirculating exhaust gas into the intake manifold is only sending inert gas into the combustion chambers to try to reduce combustion temperatures, and decrease NOx emissions. I know a lot of folks do disable them, and in some cases they notice a performance difference. YMMV.

Attached are some 1971 - 1973 engine vacuum schematics. I am betting one of them is showing your engine calibration. You will have to dig through the PDF files to find your particular engine.
Thank you! The issue is I am getting a pretty rough idle and trying to nail down whether it’s a vacuum Leak or something else. Trying to start with the simplest things first. I’ve capped some lines, but was told that EGR could cause a decent vacuum leak. I don’t have to worry about emissions so I’m trying to eliminate as many unnecessary lines as possible. Already ran the line from the carb to the distributor so eliminated all those T’s. I have 4 lines coming out of the firewall, I know one of them is for the transmission but trying to figure out which one it is.
 

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I have 4 lines coming out of the firewall, I know one of them is for the transmission but trying to figure out which one it is.

The manifold on the firewall is supplied by the engine, and is two separate "loops". One half is full manifold vacuum to the rear of the trans modulator. A length of hose from the manifold "T" goes to the loop, then another to the metal tube for the vacuum modulator. The other half of the manifold is fed from a tee in the EGR line, to the second metal trans vacuum line, then goes to the forward section of the dual area modulator. This is shown as "loop" #12 in the vacuum diagrams that mrgmhale posted. The dual area system was used to raise the shift points when the EGR system was active.

You don't really need an EGR block off plate, just get a section of a non-rubber gasket material and make your own gasket without holes for the EGR passages. High temp material would be best, but for purposes of testing and tuning, any material would be fine. If you spray around the base of the carburetor with carb clean, a change in idle speed or smoothness would indicate a vacuum leak.



1655563681765.png
 
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Thank you! The issue is I am getting a pretty rough idle and trying to nail down whether it’s a vacuum Leak or something else. Trying to start with the simplest things first. I’ve capped some lines, but was told that EGR could cause a decent vacuum leak. I don’t have to worry about emissions so I’m trying to eliminate as many unnecessary lines as possible. Already ran the line from the carb to the distributor so eliminated all those T’s. I have 4 lines coming out of the firewall, I know one of them is for the transmission but trying to figure out which one it is.
A leaking EFR valve can definitely cause a rough idle. But, unlike a vacuum leak it will not lean out the A/F mixture, as it has no Oxygen in it. It is basically an inert blend of gas which is meant to occupy volume in the combustion chamber with a non-volatile capability. That caused the combustion temperatures to drop and reduces NOx emissions. A vacuum leak, on the other hand, will lean out the A/F ratio, which will also cause a rough idle, but for different reasons than a leaking EGR valve.

The few leaking EGR valves I have were obviously clogged with carbon and other crud when I would replace them. If you do take yours off to inspect it for something keeping its pintle valve from seating, be sure you have a new high temperature EGR gasket available to install.
 

PeteG41

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The manifold on the firewall is supplied by the engine, and is two separate "loops". One half is full manifold vacuum to the rear of the trans modulator. A length of hose from the manifold "T" goes to the loop, then another to the metal tube for the vacuum modulator. The other half of the manifold is fed from a tee in the EGR line, to the second metal trans vacuum line, then goes to the forward section of the dual area modulator. This is shown as "loop" #12 in the vacuum diagrams that mrgmhale posted. The dual area system was used to raise the shift points when the EGR system was active.

You don't really need an EGR block off plate, just get a section of a non-rubber gasket material and make your own gasket without holes for the EGR passages. High temp material would be best, but for purposes of testing and tuning, any material would be fine. If you spray around the base of the carburetor with carb clean, a change in idle speed or smoothness would indicate a vacuum leak.



View attachment 64647
Yep I’ve been going over this vacuum diagram for a bit now. I have a new gasket for the EGR on the way, and am going to cut 1/4” aluminum for a plate. I have eliminated the lines and T’s at the check valves, and just routed the line from the distributor to the carb. Looks a little cleaner and less connections to hide a leak. I’m assuming the vacuum lines that come out of the firewall, loop around and go back in are the transmission lines
 

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I’m assuming the vacuum lines that come out of the firewall, loop around and go back in are the transmission lines

The transmission vacuum line manifold is circled below. The lines don't go through the cowl panel, the plastic manifold is the loop and is screwed to the panel.

1655663080988.png
 

PeteG41

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The transmission vacuum line manifold is circled below. The lines don't go through the cowl panel, the plastic manifold is the loop and is screwed to the panel.

View attachment 64684
Ok awesome. I don't think the line on the far right was connected to anything in my case, but it looks like it might go to a port on the back of the carb? I didn't pull any of those off and obviously won't. I also assumed a couple of those lines were responsible for heat/ac inside the cabin.
 
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Ok awesome. I don't think the line on the far right was connected to anything in my case, but it looks like it might go to a port on the back of the carb? I didn't pull any of those off and obviously won't. I also assumed a couple of those lines were responsible for heat/ac inside the cabin.
The two smaller diameter vacuum lines are used to get Ported Vacuum to the Dual Diaphragm Transmission Vacuum Modulator. One of the lines is shared, via a vacuum tee, with a vacuum line that connects to the EGR diaphragm. The other vacuum line connects to the smaller diameter steel tube that leads from the rear of the engine compartment to the transmission vacuum modulator for the transmission. On the tranny dual diaphragm modulator the Ported Vacuum goes the the smaller port on the side of the modulator located on the more forward position.

The larger modulator vacuum port on the modulator is either on the very rear of the modulator, or sometimes it is also a side oriented port, but located toward the rear of the vehicle (depending on the design of the dual diaphragm modulator - I have seen them both ways).

Following is a link to a YouTube video I put together a little while ago. The first part of the video is more oriented toward info on how the Ported Vacuum is managed by the Thermal Vacuum Switches (3 port and 2 port switches). The later part of the video shows how the Ported and Manifold Vacuum lines are connected to a Dual Diaphragm (Two Port) Transmission Modulator. I hope folks can make sense of the info in the videos.

 

PeteG41

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The two smaller diameter vacuum lines are used to get Ported Vacuum to the Dual Diaphragm Transmission Vacuum Modulator. One of the lines is shared, via a vacuum tee, with a vacuum line that connects to the EGR diaphragm. The other vacuum line connects to the smaller diameter steel tube that leads from the rear of the engine compartment to the transmission vacuum modulator for the transmission. On the tranny dual diaphragm modulator the Ported Vacuum goes the the smaller port on the side of the modulator located on the more forward position.

The larger modulator vacuum port on the modulator is either on the very rear of the modulator, or sometimes it is also a side oriented port, but located toward the rear of the vehicle (depending on the design of the dual diaphragm modulator - I have seen them both ways).

Following is a link to a YouTube video I put together a little while ago. The first part of the video is more oriented toward info on how the Ported Vacuum is managed by the Thermal Vacuum Switches (3 port and 2 port switches). The later part of the video shows how the Ported and Manifold Vacuum lines are connected to a Dual Diaphragm (Two Port) Transmission Modulator. I hope folks can make sense of the info in the videos.

Thank you!! Super informative, and funny enough I just watched your fuel pump video last week before I replaced mine. I haven't disconnected any of the transmission vacuum lines, I definitely know that much. I did remove some of the lines at the check valves in front, and routed the distributor vacuum line to the carb, kinda just eliminating the rest. I had the vacuum diagrams pulled up that another member had shared with me, but I was having some trouble since in all of the pictures there were only 2 ports. I am trying to remember but can double check when I get home, but I think the far left line, #4?, wasn't connected to anything, but I am assuming it goes to the T on the back passenger side ports.
 
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Thank you!! Super informative, and funny enough I just watched your fuel pump video last week before I replaced mine. I haven't disconnected any of the transmission vacuum lines, I definitely know that much. I did remove some of the lines at the check valves in front, and routed the distributor vacuum line to the carb, kinda just eliminating the rest. I had the vacuum diagrams pulled up that another member had shared with me, but I was having some trouble since in all of the pictures there were only 2 ports. I am trying to remember but can double check when I get home, but I think the far left line, #4?, wasn't connected to anything, but I am assuming it goes to the T on the back passenger side ports.
Those vacuum line connections can get pretty wild from back in the 70s. The attached file was sent in an earlier post in this thread, but I have included it in this post to prevent any confusion. On this files 22nd page you will see a list of engines for 1973, and the model vehicles they came in. There are two entries for 351 2v engines in Mustang for calibrations 3-14A and 3-14D on pages 70 & 72 (original document's pages 66 & 68). Pages 76 & 77 have calibrations for two different 351 4v engines (one with auto tranny, one with manual) for calibrations 3-15A and 3-16A that were not in the original document in case you have a 4v engine.

I am pretty sure you mentioned it was a 351 2v engine. If you have the original valve covers there ought to be a calibration tag on it, but they are often gone after all these years. In any event, your engine should look like one of the calibrations shown. In some ways the vacuum routing is similar to what we have on our 302, in other ways it will be different. I hope all that does not end up becoming too confusing, especially after so many changes that may have been done on the engine over the years. Getting the vacuum lines straightened out may prove to be almost overwhelming if there has been a lot of modification over the years. The big deal is to make certain no changes to the Ported Vacuum lines eaves any of the vacuum lines unplugged when no longer in use (EGR Valve), otherwise you won't get proper vacuum from the Ported source to the Vacuum Modulator's 2nd Ported connection, nor to the distributor's Ported Vacuum Advance Diaphragm.
 

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  • 1973Mustang_VolumeVI_EmissionControlSystems_Chapter6_20210210.pdf
    5.2 MB · Views: 4

PeteG41

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Those vacuum line connections can get pretty wild from back in the 70s. The attached file was sent in an earlier post in this thread, but I have included it in this post to prevent any confusion. On this files 22nd page you will see a list of engines for 1973, and the model vehicles they came in. There are two entries for 351 2v engines in Mustang for calibrations 3-14A and 3-14D on pages 70 & 72 (original document's pages 66 & 68). Pages 76 & 77 have calibrations for two different 351 4v engines (one with auto tranny, one with manual) for calibrations 3-15A and 3-16A that were not in the original document in case you have a 4v engine.

I am pretty sure you mentioned it was a 351 2v engine. If you have the original valve covers there ought to be a calibration tag on it, but they are often gone after all these years. In any event, your engine should look like one of the calibrations shown. In some ways the vacuum routing is similar to what we have on our 302, in other ways it will be different. I hope all that does not end up becoming too confusing, especially after so many changes that may have been done on the engine over the years. Getting the vacuum lines straightened out may prove to be almost overwhelming if there has been a lot of modification over the years. The big deal is to make certain no changes to the Ported Vacuum lines eaves any of the vacuum lines unplugged when no longer in use (EGR Valve), otherwise you won't get proper vacuum from the Ported source to the Vacuum Modulator's 2nd Ported connection, nor to the distributor's Ported Vacuum Advance Diaphragm.
Yessir I have the 2v. The numbered picture is definitely helpful! It is a little overwhelming when I just start looking at it, with the check valves and lines everywhere, but I think I can sort through it. The emissions lines I have bypassed I've made sure to cap. The plan is to keep the essential lines, and eliminate the rest just to try and clean everything up. I want to limit my time of hunting down hidden vacuum leaks, which I am sure will drive me a little crazy. The valve covers are in great shape visually but I think the tag is long gone.
 
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