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  1. #1

    Default 83 5.0 runs worse with EGR

    In trying to get my '83 to pass smog, i discovered that my EGR tube was disconnected. I hooked it back up, went for a long ride, and experienced a really bad, restricted, sputtering ride. When I disconected and plugged the rubber tube, the ride was great. Im all for getting things in working order so Id like to know what would be causing this? I check my hard plastic lines and rubber tubing, visually all looks ok. The EGR valve was replace 1000 miles ago by my carb rebuilder and as of yesterday, I installed new plugs wires, air, fuel filters pvc, etc. Thanks y'all.

  2. #2
    FEP Senior Member Matt J's Avatar
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    It's always possible that the EGR itself is failing, even if it is fairly new. I'm assuming your carb guy disconnected it on purpose, figuring that because it's running great without it and you only had this done 1,000 miles ago. It's not too likely that you got the car back with the EGR plugged in and it running great, then it just came undone and suddenly runs bad when plugged in...Is it possibly the wrong part, or is it leaking? Are you sure he actually replaced it? Seems weird to replace the part and not connect it. It might be worth asking your guy what he did...

    Generally, these cars are old enough that there are several things wrong with them that have been incorrectly "fixed" by someone else in the past. When you find something not right and fix it correctly, the old "fix" that was done to hide the original problem now causes a new set of problems. As much as a PITA as those emissions tests are for an older car like this, they're pretty good at showing when something isn't right, even if it feels like the engine is running well. If it's running rough when the EGR is plugged in, I'd have to assume that it's a problem with that part. I'm not a carb expert, though, someone else will have to help you with that!

  3. #3

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    Everything runs worse with EGR, lol

    "... really bad, restricted, sputtering ride. When I disconected and plugged the rubber tube, the ride was great."


    ... tells me the EGR is open full time and/or when it's not supposed to be, by the incorrect vacuum line being connected to it. If your car failed "smog" due to what they deem to be too-high NOx, that points a finger at a non-functioning EGR. The inclusion of exhaust gas recirculation on a running engine can be finicky and specific (look at your vacuum line routing decal under the hood or up on the hood's underside (or search here to find yours if yours is missing or illegible)) as to when it adds exhaust gases to combustion, what vacuum source and hose it's connected to, and whether a temperature vacuum switch is also supposed to be in it's black spaghetti circuit.

    Very basically, with a carburetor, the initial "old school" hookup of EGR to vacuum was only ever to ported vacuum, never to full vacuum (so never at idle, but off idle, and/or temperature-switched as well).
    Last edited by Walking-Tall; 08-15-2016 at 03:58 PM.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  4. #4

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    Maybe the wrong EGR valve was replaced with the wrong part ? This is an original EGR valve from an '83, 5.0 GT with the vented diaphragm.

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  5. #5

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    Here's a pic of the valve that's installed now.



    Here is what the tube plugs into. The two green lines.



    My emissions sticker.



    Sent from my iPhone using Tapatalk

  6. #6

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    Mine doesn't have any markings left on it, but does look exactly like yours does from the "top" view.

    Back in the day, (the 90's), when my EGR valve "failed" it wound up damaging the catalytic converter. The felt ring over the vent holes dried up and was just leaking vacuum. Therefore, not enough vacuum to everything tee'd off the same line; including the diverter valve that sends air from the smog pump, downstream to the cat. conv.

  7. #7

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    The EGR valve used on the carbureted GTs is what's known as an integral backpressure sensing EGR valve. The
    valve does not hold a vacuum, unless exhaust backpressure is present at the valve tip, to close the regulator
    pintle. This mechanism is also used to regulate the position of the EGR valve when driving at part-throttle.

    If the current EGR valve holds a vacuum without the engine running, it's defective, and will cause surge. Also
    make sure the EGR vacuum circuit is connected to the vacuum nipple that's above and forward of the choke
    spring unit. Any other port will not give the correct EGR vacuum signal.

    The external appearance of the EGR valve is not the most important thing. If you look at the photo posted by
    jessesandy, note the hat-shaped insert over the one port. Devices like this are used to tune the EGR valve flow
    to a specific application, and replacement valves usually will come with an assortment of restrictor washers,
    and instructions about which ones to use where, based on the original valve that was being replaced. Problem
    is, if the numbering from the original valve wasn't transferred to the new one, the next person to replace that
    valve won't know what bits to use.

    Also make sure the canister purge system is properly connected, with all the indicated restrictors in place.
    The purge system is controlled by EGR vacuum. Excessive canister purge flow can also contribute to surge.

    And definitely make sure the vacuum advance system is working properly as well. If it's not, you will get part-
    throttle surge when the EGR is active.
    Last edited by JACook; 09-02-2016 at 02:11 AM.
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    2012 F150 S-Crew 4x4 5.0 "Blue Coyote"... 65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ...
    '68 Vert, Mexican block 307 4-speed... '71 Datsun 510 ...
    And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

  8. #8

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    I've finally had time to tinker over the holidays. I had to take out the carb and it turned out it had a defective power valve which was spill fuel everywhere. The carb shop was pretty good about giving it a second look. I was pretty surprised to find out it's not the original carb. I'm missing the stamped Ford part number on the carb. Is this even a 4180c? It doesn't look like any of the images I've seen of one.



    I was feeling pretty confident the carb would take care of my smog issues, along with new plugs and wires and a new catalytic converter. But the smog test only shop couldn't begin the dyno test since I still have the bucking, surging problem at the 15 and 25mph. The smog test cancels the due to inconsistent speed.

    Frustrated, I went back to do the free smog retest with an unplugged EGR valve. Low and behold the bucking stopped and I was able to get a test out of it, albeit it was a failed test but not buy much. But I did get a readout to see what I'm working with. My NO numbers failed.



    Now if I could get my EGR system working right. I went through my vacuum hoses to check for anything obvious. I removed the EGR valve to see what I'm working with. But didn't see anything with my limited knowledge. Diaphragm moves when pushed. I took a look at the valve with the engine revved at 2k rpm. I did see the diaphragm open but it wasn't a smooth movement. When I held the rpm the valve diaphragm seemed to bounce up and down a bit. Could be his be consistent with the bucking problem I'm having?



    The knowledge on this site has been so valuable but I'm afraid to go further since I don't want to damage any old vacuum tubing and cause myself more problems! There has to be a vacuum leak somewhere that I'm just not seeing. I also checked my vacuum advance diaphragm and it holds. My rotor is a bit slow to snap back when moved CCW. I did oil it as was suggested in other threads but it's not very snappy.

    I'm this close to dropping off the car to a STAR Test-and-Repair station where they MIGHT fix my bucking and smog problem but they will surely dig into my pockets!









    Sent from my iPhone using Tapatalk

  9. #9

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    If I see your photograph right, that's a LIST-8207, a 4160 series 600cfm vacuum secondary, that somebody's put the 4180 bowls onto. It's a rare bird, with no trick/rebuild/renew kit number even listed for it. Though that shouldn't deter you from continuing to use it, because it's similar enough to any other 4160 600cfm to be able to piece together a "kit" if/when needed.

    The 8207 is factory calibrated (should be similar enough to a 4180) as follows:
    - #622 "close limit" primary main jets
    - "39" secondary metering plate, with Ø0.029" idle feed restrictions and Ø0.073" main "jet" holes
    - 8.5in-Hg primary power valve
    - Ø0.031" primary accelerator pump shooter
    - Plain vacuum secondary spring

    You might have to dig down under the "breaker" plate in the distributor, because things might be "adjusted" under there, or a spring's broken etc., to provide a very fast (too fast?) mechanical advance curve, which would also ramp up the "NO", similarly to no EGR bringing it down. You can, through the window in the "breaker" plate, bend the outer spring tabs outward to increase the advance springs' tension... I'm bringing that up because of your observation that your rotor doesn't seem to snap back to what is initial timing...

    I can't speak to "correct" EGR function (because it's nothing but a band-aid of dysfunction IMHO), besides that it needs to be applied at specific times if it is used. Hopefully somebody else more in-the-know will address that.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  10. #10

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    The tube coming out of the side of the metering block is the ported vacuum. In the picture it looks like it's plugged.

    The small tube on the front of the throttle body is probably manifold vacuum and not a "spark port" like the 4180.

  11. #11

    Default

    Those high NOx numbers are the primary reason EGR exists. But your replacement carburetor does not
    have an EGR vacuum source, so I'm wondering what you're hooking the EGR system up to. That flat pad
    above and to the front of the choke unit is where the EGR system would have connected to on the original
    carb.

    Connecting the EGR system to the distributor ported vacuum source is a recipe for driveability problems.
    Connecting the EGR system to manifold vacuum is even worse. And +1 what mriggs said. The nipple on
    the metering block is for distributor ported vacuum, which can also be used to operate the purge system
    and thermactor diverter, but cannot be used to operate EGR.
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    2012 F150 S-Crew 4x4 5.0 "Blue Coyote"... 65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ...
    '68 Vert, Mexican block 307 4-speed... '71 Datsun 510 ...
    And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

  12. #12

    Default 83 5.0 runs worse with EGR

    Quote Originally Posted by JACook View Post
    Those high NOx numbers are the primary reason EGR exists. But your replacement carburetor does not
    have an EGR vacuum source, so I'm wondering what you're hooking the EGR system up to. That flat pad
    above and to the front of the choke unit is where the EGR system would have connected to on the original
    carb.
    I was able to trace this tube back the vacuum tubes that connects to vacuum tree by the EGR.



    The black line next to the green line in this pic is what connect to the line above.


    Sent from my iPhone using Tapatalk
    Last edited by FriscoNotch; 01-01-2017 at 11:42 PM.

  13. #13

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    Quote Originally Posted by JACook View Post
    That flat pad above and to the front of the choke unit is where the EGR system would have connected to on the original
    carb.
    Interesting... the correct EGR vacuum source is similar then to the vacuum secondary's source signal, Jeff? That doesn't seem right, high venturi velocity (vacuum) creating the signal... but I guess if that's how they did it, it must work. I can see on a number of 4160 castings I have here, while not drilled, are there, the flat pads, that is... a passage drilled straight into that upper flat pad, and then there's another cast flat pad that would interconnect below it, that's aimed right at the venturi diameter... drill those two passages, block the lower outer with lead shot or other, and add a vacuum nipple to connect with EGR... I'd have to look down the throat of a 4180, because I have no clue whether the second drilling is to lead clear out into the primary venturi, or elsewhere, downward and elsewhere in the carb body....
    Anyway, one way or another, the correct source should be able to be replicated.
    Last edited by Walking-Tall; 01-01-2017 at 11:36 PM.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  14. #14

    Default

    The port coming out of the body on the 4180 is different depending on application.



    On the truck carbs it hooks to a small hole in the venturi but on the Mustang carbs it doesn't.

    There is a hole drilled down to the throttle body.



    That connects to a passage milled into the throttle body which goes to a hole that is blocked from manifold vacuum when the throttle is closed (ported vacuum).



    To the left of that hole you can see the curb idle [with needle sticking out of it] and the transfer slot. To the left of that is the "spark port" which has a small hole above the [closed] throttle plate and one hole below it. This is what feeds the small tube on the front of the throttle body. The signal from this port doesn't shut off vacuum completely when the throttle is closed. Instead, the vacuum is lowered just enough to retard the timing but some vacuum is still present. I assume this was done so the vacuum advance would react more quickly when the throttle is opened.

    The truck carbs do not have this spark port. Instead there is a single hole above the throttle plate that feeds the small tube on the front of the throttle body (ported vacuum).

  15. #15

    Default

    The ported vacuum off of the metering block on your 4160 is the same thing as the "EGR" port on the Mustang 4180. It's routed completely different but the destination is the same, a hole in the throttle body that is blocked from manifold vacuum when the throttle is closed.

    The 4160 does not have a "spark port" equivalent to the Mustang 4180 [I don't think any carbs do]. If your vacuum advance is hooked to the small port on the throttle body then you should check if that is manifold vacuum [vacuum present when the throttle is closed]. If it is then move the vacuum advance to the ported vacuum. "T" into the big rubber line before it connect to the small hard line (which I now see).

    That hard line runs to a blue thermal switch which should block the black line and vent the green line when the engine is under 130 degrees. When the engine is above that temperature, the switch should hook the green line to the black line. These switches can wear out and cause vacuum leaks. You can test it with a hand-held vacuum pump. With the engine cold, hook the pump to the switch where the black line goes, it should hold vacuum. Now warm up the engine and try it again. It should not hold vacuum with nothing hooked where the green line went. Put your finder over the open port (or put a cap on it), now it should hold vacuum.

  16. #16

    Default

    Quote Originally Posted by mrriggs View Post
    The port coming out of the body on the 4180 is different depending on application.



    On the truck carbs it hooks to a small hole in the venturi but on the Mustang carbs it doesn't.

    There is a hole drilled down to the throttle body.



    That connects to a passage milled into the throttle body which goes to a hole that is blocked from manifold vacuum when the throttle is closed (ported vacuum).



    To the left of that hole you can see the curb idle [with needle sticking out of it] and the transfer slot. To the left of that is the "spark port" which has a small hole above the [closed] throttle plate and one hole below it. This is what feeds the small tube on the front of the throttle body. The signal from this port doesn't shut off vacuum completely when the throttle is closed. Instead, the vacuum is lowered just enough to retard the timing but some vacuum is still present. I assume this was done so the vacuum advance would react more quickly when the throttle is opened.

    The truck carbs do not have this spark port. Instead there is a single hole above the throttle plate that feeds the small tube on the front of the throttle body (ported vacuum).
    I saw that extra hole in the 4180 bodies and the passage in the 4180 throttle bases on 'net search pictures, and wondered by it's location whether or not it connected with the EGR nipple up top. What you've shown and explained here (thanks very much), and your last post including explaining the thermal switches incorporated for EGR function as well, might be the most in-depth 4180 information on the internet. Trust me, I looked and looked regarding this subject, and it's just not out there... and whaddaya know, nothing new under the sun, ported vacuum for EGR.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  17. #17

    Default

    Quote Originally Posted by Walking-Tall View Post
    Interesting... the correct EGR vacuum source is similar then to the vacuum secondary's source signal, Jeff? That doesn't seem right
    You're right. But that port on the 4180C has nothing at all to do with the secondary diaphragm vacuum. It connects
    to a timed port in the passenger-side primary throttle plate bore.


    Quote Originally Posted by mrriggs View Post
    The port coming out of the body on the 4180 is different depending on application.


    I disagree with this statement. That ^^^ port is an EGR port on every car and truck 4180C I've seen. And I've seen
    (and own) a fair number of them.

    Quote Originally Posted by mrriggs View Post
    The ported vacuum off of the metering block on your 4160 is the same thing as the "EGR" port on the Mustang 4180. It's routed completely different but the destination is the same, a hole in the throttle body that is blocked from manifold vacuum when the throttle is closed.

    The 4160 does not have a "spark port" equivalent to the Mustang 4180 [I don't think any carbs do]. If your vacuum advance is hooked to the small port on the throttle body then you should check if that is manifold vacuum [vacuum present when the throttle is closed]. If it is then move the vacuum advance to the ported vacuum. "T" into the big rubber line before it connect to the small hard line (which I now see).
    The 4160 distributor ported vacuum source is not equivalent to the EGR vacuum port on a 4180C. EGR vacuum does
    work similarly to distributor ported vacuum, but EGR vacuum is timed later in the throttle opening. Because the
    distributor vacuum is timed earlier, and because the EGR valve bleeds vacuum to regulate EGR flow, the EGR system
    will not function properly if it's connected to the distributor vacuum source, and the vacuum advance system will not
    function properly if it's vacuum source is shared with the EGR system.

    The Mustang 4180C does have some manifold vacuum bleed into the distributor spark port source, to provide a small
    amount of vacuum advance at idle, and the nipple is in a different place, but otherwise it works the same as the distributor
    ported vacuum source on any other Holley carb.
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    2012 F150 S-Crew 4x4 5.0 "Blue Coyote"... 65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ...
    '68 Vert, Mexican block 307 4-speed... '71 Datsun 510 ...
    And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

  18. #18

    Default

    Quote Originally Posted by JACook View Post
    The 4160 distributor ported vacuum source is not equivalent to the EGR vacuum port on a 4180C. EGR vacuum does
    work similarly to distributor ported vacuum, but EGR vacuum is timed later in the throttle opening. Because the
    distributor vacuum is timed earlier, and because the EGR valve bleeds vacuum to regulate EGR flow, the EGR system
    will not function properly if it's connected to the distributor vacuum source, and the vacuum advance system will not
    function properly if it's vacuum source is shared with the EGR system.
    Are you sure about that? If anything, the EGR port would come in sooner than ported. Looking at the 4160 throttle plate next to the 4180, the hole for the ported vacuum on the 4160 is completely above the closed throttle blade where the hole for the EGR on the 4180 is partially covered by the throttle blade.

    The "EGR" port on the truck 4180 (List#50003) I'm looking at does not go all the way to the throttle bore. It's drilled down to the throttle body the same as the mustang carb but the passages in the throttle body are not drilled. Instead, there is a hole drilled through the side of the carb body that intersects the passage and feeds directly to the venturi. The hole was then plugged on the outside of the carb so the "EGR" port sees only venturi vacuum. I suppose this is not how ALL truck carbs are plumbed. They used the 4180 on trucks, big and small, from 1979 to 1991 so there is likely many variations.
    Last edited by mrriggs; 01-02-2017 at 03:11 PM.

  19. #19

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    Looking at vacuum diagrams from older trucks I think I see what the venturi vacuum was used for. The EGR valve is hooked to ported vacuum through a thermal switch like the cars but there is also a an "EGR load control" inline. The diaphragm if the EGR load control is hooked to venturi vacuum. I suspect that under heavy load the venturi vacuum closes the EGR load control which cuts off the EGR valve from ported vacuum. This would have been necessary on a heavily loaded big-block truck since there would be enough manifold vacuum, even at full throttle, to keep the EGR valve open.

    The truck carb I have also has a power valve vent for this same reason. The power valve vacuum well is fed to the manifold through a restrictor and is also plumbed through the throttle shaft up to the top of the carb. The throttle shaft is drilled so that at full throttle it opens the power valve vacuum well to atmosphere. Again, this was done to prevent the manifold vacuum on a heavily loaded truck from closing the power valve at full throttle.

  20. #20

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    Quote Originally Posted by mrriggs View Post
    The truck carb I have also has a power valve vent for this same reason. The power valve vacuum well is fed to the manifold through a restrictor and is also plumbed through the throttle shaft up to the top of the carb. The throttle shaft is drilled so that at full throttle it opens the power valve vacuum well to atmosphere. Again, this was done to prevent the manifold vacuum on a heavily loaded truck from closing the power valve at full throttle.
    Yup, from what I've seen, this is common mechanical trickery, often where a too-small carburetor is atop a large engine. The "1.21" Motorcraft 2-barrel I had on my V6 for a time, that began life on a '74 F250 with 390 engine, also had a power valve vent to atmosphere up top between the venturi, and no direct passages to the throttle bores for manifold vacuum, but a drilled passage from the power valve vacuum chamber to the middle of the throttle shaft bore. The throttle shaft has a machined round "indent" in it there between the bores, which allows direct manifold vacuum up until about 1/2 throttle, after that it's virtually closed off, so that the power valve would remain open. IMHO, all such trickery is corner-cutting to actual tuning and dialing in and giving an engine what it wants to function efficiently, and forcing things to do what they otherwise wouldn't, isn't ever usually better. Also IMHO, a larger carburetor on a large engine, dialed in, would function much more efficiently. I blocked the PV vent, and filed notches in the throttle base into the throttle bores for full time manifold vacuum to act upon the power valve diaphragm, for the reasons of the trickery not being necessary, most definitely not on my little 3.8 V6.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  21. #21

    Default

    Quote Originally Posted by JACook View Post
    You're right. But that port on the 4180C has nothing at all to do with the secondary diaphragm vacuum.
    No, of course not.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  22. #22

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    I think I was wrong about how the "EGR load control" works. I found the following here; http://www.waybuilder.net/sweethaven...Num=4&modNum=7

    There are two different methods of supply vacuum to the EGR valve. The first method uses a vacuum port into the carburetor throat located just above the throttle plate. As the throttle begins to open, vacuum will begin to be applied to the port and operates the EGR valve. The valve will continue to operate fully until approximately half throttle is reached. As the throttle is open past the halfway point, exhaust gas recirculation gradually will diminish to zero, as the throttle approaches the fully opened position.
    The second method uses a vacuum port that is directly in the carburetor venturi (fig. 4-53). The carburetor venturi provides vacuum for the EGR valve any time the engine is running at high speed. The problem with using venturi vacuum is that it is not strong enough to open the EGR valve. So to make it work, manifold vacuum is used to operate the EGR valve through a vacuum amplifier. The vacuum amplifier switches the manifold vacuum supply to the EGR valve whenever venturi vacuum is applied to its signal port. At times of large engine loading (wide, open throttle), manifold vacuum will be weak, producing the desired condition of no exhaust gas recirculation.
    So the venturi vacuum was used to open the EGR valve, not close it. The loss of manifold vacuum feeding the EGR through the "amplifier" at WOT is still responsible for closing the EGR valve. I imagine this setup would turn on the EGR later than if the EGR valve was hooked directly to ported vacuum. Probably delaying the EGR until the main fuel circuit kicks in.

  23. #23

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    So, I think as solution to the OP, by the RPM/MPH that "they" are testing at and "NO" is not being reduced enough to pass inspection, it would seem that your EGR system is simply not yet getting actuated at those lower RPM/MPH test samplings. This certainly gives credence and attention necessary to mrriggs' findings of the ported EGR throttle base passage being lower in the bore, more or less RIGHT off-idle, pretty much as soon as the throttle is even looked at, which is sooner than vacuum is available at the metering block vacuum nipple where your EGR system is presently connected.

    This isn't an easy fix unless you're handy with drilling and modifying the carburetor. I would suggest in the meantime, if you're pressed for time and the inspection needs to get passed asap, and until you can properly address this situation with either a 4180 back into the situation or your 4160 (that passes their visual inspection) modified to correctly actuate the EGR, the "NO" is usually brought down by retarding the initial timing some. As well, you should examine how much mechanical advance is getting brought in, how soon, because it sounds like it might be pretty quick, which could also explain the higher "NO" readings. The bucking/surging business could be a combination of over-advanced ignition timing coupled with EGR introduced at the wrong time.

    If you're not familiar, here's a good article for learning, understanding, and modifying a Duraspark distributor's workings:
    http://www.fordmuscle.com/archives/2000/03/timing/

    EDIT: re-read above, and those test samplings were with EGR disconnected? How that passes the "visual", no idea. Anyway, hopefully the information above is still helpful for you.
    Last edited by Walking-Tall; 01-02-2017 at 08:07 PM.
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  24. #24
    FEP Super Member erratic50's Avatar
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    Quite the predicament above. Makes me wonder what state's emissions you are trying to meet.

    Depending upon their rules and your know-how and your preferences you may want a different approach entirely.

    Without starting a war of carb vs EFI, etc, in this thread it occurs to me through some outside the box thinking that it could become less expensive in the long run to swap over to an 86-93 EFI configuration. Granted a parts stash with manifold, injectors, wiring, fuel pump and pickup, etc is all required. Guys like me with only slightly newer cars they've upgraded have those factory parts on hand.

    Also there is the aftermarket if you have deep pockets.

    Unless you can track down the correct 35 year old Mustang specific Holley carb that is.

    For me being in the Midwest where it's very cold tonight, 7 now and 0 by morning - I have always absolutely loved my EFI. Light off the old beast and drive away..... Goodbye drivability issues.

    Bear in mind I'm simply trying to help - I know there are a lot of guys that dislike EFI and I totally respect that. I simply know what it's like to own a car that has issues what it's like to be soaked in gas from the how many-ith time I've tore apart a carb trying to keep it working properly. Pop back out the carb just one time and if you are as unlucky as I am your powervalve is toast. Starting such a misbehaving car cold each morning just to drive somewhere gets to be a very expensive "hobby"!after a while like it was for me when my daily acted this way. Especially when the nearest parts store with the supply is 35 miles away and they suck fuel terribly when the PV is out..

    Anyway.... an amazing amount of detail in this thread about carbs that you should all be VERY proud of. Devil is in the details and it is always something!

  25. #25

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    If the blue thermal switch is working correctly and not leaking, check the other items hooked to the green line to be sure they are not leaking.

    If that all checks out then I would check the function of the diverter valve next. It's supposed to switch the smog pump air stream from the heads to the cat when the engine is warm. If the air is not being diverted then it will be pumping fresh air into the exhaust ports in the heads. The same ports that the EGR feeds from. So when the EGR valve opens, expecting a big gulp of inert gas, it gets oxygen which leans out the mixture and causes the motor to stumble. Kind of a shot in the dark but something to check.

    If that all checks out then the only thing left is the EGR valve itself. Either it's malfunctioning or it has the wrong restrictor on the exhaust input.

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