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Discussion Starter · #1 ·
Ok, so I'm not good at reading vacuum schematics. I keep getting confused. I think maybe I have a couple things connected wrong. Aside from the accessory connections stemming from the manifold on the firewall, there are only two things connected on the motor: EGR and vacuum advance. I think maybe I'm using the wrong vacuum ports for their control. Can anyone point me to the correct ports to use for them with the 2150?
 

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Discussion Starter · #3 ·
Well, on a general level it kinda matches what I'm doing. On a specific level, I don't know if I'm using the correct vacuum ports on the carburetor. When I look at a diagram, I don't know what port on the diagram matches with which port on the carburetor. If I've correctly understood stuff I've recently read, not all vacuum ports on a carb have the same amount of vacuum at the same time depending on current engine operation.
 

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Discussion Starter · #5 ·
Sorry this took so long. I kept forgetting to take a photo. So I attached this photo from my Chilton manual. Also, I don't think there was ever a thermal vacuum switch inline with the EGR.

Looking at the diagram, I'm not really sure which port is which off of the carb. Once upon a time I found a legend for those port indicators, but can't seem to locate it now.
 

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Is your carburetor stock? If so, I believe they tap in below the blades straight to the bore.
 

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Discussion Starter · #7 ·
Yeah, it's the stock 2150 2bbl carb it was given when built. At least I think it is. It was apparently rebuilt at least once given that the tag is missing.

But I was checking up on some stuff, and I think it can be possible that I have the advance and EGR connected to the wrong port, and definitely certain that I've routed the vacuum lines incorrectly. I found something that says EGR Port vaccum from the carb needs to be run to a ported vacuum switch. When cold, it runs vacuum to the advance. Once it warms up enough, it switches over to the EGR.

But, I went and double checked... This system sounds like it needs a three-port VPS, and both on my 351M are two-port. I'm not sure of the correct routing now because I noticed the diagram I posted is apparently for Canadian models, my books have no other 351 diagrams applicable for 1978, and the vacuum lines were pretty messy and appeared to be patched up however it was wanted. Each PVS had vacuum routed in such a way that they were rendered ineffective.

I did manage to find a vacuum diagram for the 400 dated for June 78, which was about a month before my car was built (as well as a couple 351M diagrams dated well after my car was built). But it includes a three-port PVS along with a pair of two-port switches. So, I'm not really sure it applies to its cousin. I'm assuming for the 400 the three-port PVS is located on the thermostat housing, whereas my 351M only has an unused port on the housing.

I kept the old vacuum lines for reference in case I needed something. But the diagrams all indicate check valves and vacuum resistors, and all pulled out were hoses, junctions, and I think just one check valve. I'm really under the impression that alterations were made in the process of conducting repairs, and stuff was removed without replacement and lines were not correctly routed.

All I really want is proper setup for just the EGR and advance, and I really can't find reliable information on how to get them routed correctly. The only vacuum lines that I know are routed correctly are from the intake manifold to the vacuum manifold on the firewall, and the choke pull-off. And I guess maybe the PCV counts, too.

For kicks I added the 400 diagram in case it's useful for the 351M.
Text Diagram Floor plan Design Font
 

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Discussion Starter · #8 ·
Is your carburetor stock? If so, I believe they tap in below the blades straight to the bore.
It wasn't until I wrote all that, that what you mentioned clicked in my head. Are you talking about this little guy here with the red cap?
 

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Discussion Starter · #9 ·
So, that port is 1/4". There is another port on the other side (this one is passenger side, the other is driver side). It's a little higher, above the throttle plate, but it's 3/16", like all the bits that need to connect. And I think it may have been connected to the rat's nest for the advance.
 

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Discussion Starter · #10 ·
Ok, looking at the leftover vacuum parts, this is what I had that wasn't a connector or old hose. The white one has a label of "DIST", which likely means it was part of the advance circuit. The blue one has a label of "A/CLR", which I take to mean that it was part of the air cleaner intake diverter to bring in hot air from along the manifold. That whole circuit was chucked because the bi-metal switch was broken along with the vacuum motor on the snorkel. Finding replacements ended up being a fruitless endeavour.
 

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Discussion Starter · #11 ·
Sorry for so many posts...

But I think I may have found something helpful, let me know if my understanding is correct.

So, I think right now advance and EGR are both running off the advance port on the carb. This would be the port next the choke, correct?

And that port with the red cap in the above photo is actually in the EGR spacer plate (located on the front passenger side of the carb). So, would that be the EGR vacuum port, then? Because it's starting to seem like the next port up, which is on the front driver side, would be the emissions vacuum port.
 

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I think (emphasis on "think") Mr. red cap is EGR. As far as the other port, not really sure.

I gotta get me an old carbeurated something or other again to play with.
 

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Discussion Starter · #13 ·
Ok, so I'm dealing with this same issue on another car where I'm rolling back a VV 7200 on a 351W with sensors and solenoids everywhere down to a 2150 and vacuum control. Between some info in a Chilton manual and a diagram from a different service manual, I think I have it worked out. The red capped port will stay capped, and the ports on the passenger side, and the driver side on the front, are what will get used. I drew up a diagram based on everything I had on hand.

It uses a blue ported vacuum switch (fully switched at 95°F). It doesn't have the vacuum circuit for overheating. I learned that requires a red ported vacuum switch (open at 235°F) with three ports to switch between ported vacuum and manifold vacuum. My engine doesn't have one. Just two 2-port switches: blue and yellow (open at 133°F?). I think the yellow one is used to control something that's not necessary and has been removed, but it's hard to tell from diagrams I've seen.

I attached the diagram I drew. Any thoughts?

 

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Discussion Starter · #15 ·
I'm wrong about the trans being in there. It's only supposed to have manifold vacuum, but the circuit description included it for whatever reason.

This has gotten to be even more fun because I'm trying to complete the identical task on another car for which the variable venturi and a host of sensors amd solenoids needed to be removed ('79 Mercury with 351W, but both manufactured in '78).

While I'm at it, I'm also trying to make sure that in both of these cars the warm air diverter system works. Especially for the LTD because I like driving it in winter time, and it's been atrocious with getting it going on cold days. At least for this I know that I just have to tap into the manifold vacuum, which is easily done. In both cases, though, I need to make sure the bi-metal switch and the thermal vacuum switches work. Each has a bi-metal switch and TVS in the air cleaner.

I don't think they're quite configured the same, but not really sure. Makes me wish I hadn't removed the vacuum lines for this system in the LTD. Anyway... In the Merc manifold vacuum runs to the bi-metal switch (3/16), then the TVS (3/16), then to the snorkel vacuum motor (1/4). However, the LTD seems different, wherein it runs to the TVS first (1/4), then to the bi-metal (3/16), then to the snorkel vacuum motor (1/4). I'm guessing on the LTD since there are only two 1/4 nipples and the rest are 3/16". The Merc is still all connected except for a source vacuum line, but the manifold tree has an open 3/16" nipple, I think. In either case I've tested the vacuum motors, and they work, but in the LTD it needs to be replaced because the hook on it for the air door is broken, so the air door doesn't move.

So, how do I go about testing the thermal components to make sure they work correctly? And why would there be two thermal-based vacuum switching components in this circuit?
 

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Discussion Starter · #16 ·
Ok, it's all completely figured out now. A person I've been working with on supplying parts found the appropriate factory diagrams for laying out the vacuum lines. All in all it turns out that what I thought were screwed up and redundant vacuum circuits were actually correct circuits, but at some point pieces in the circuits were removed.

So, the spark advance is connected to the EGR port. It branches into two circuits before coming back together to handle spark advance. On one branch it's controlled by a vacuum delay valve, on the other controlled by the blue ported vacuum switch on the thermostat housing.

The EGR circuit is similar except it uses the spark port and a yellow ported vacuum switch mounted at the front of the block.

The TVS runs the air diverter valve for the Thermactor system and is sourced from the spark port. The warm air diverter is powered by manifold vacuum from a port at the front of the manifold and passes through the bi-metal switch with no cold weather modulator. Gotta figure out how to get vacuum to the warm intake air circuit since the manifold port it should use was damaged and I was forced to patch it.

So, all in all, I'm pretty happy about getting this figured out. I think my diagram should still be good for my '79 Mercury 351W.
 

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Good deal ledzilla! If you have a copy of that diagram feel free to post it here as it may help others in the future.
 

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Ok, it's all completely figured out now. A person I've been working with on supplying parts found the appropriate factory diagrams for laying out the vacuum lines. All in all it turns out that what I thought were screwed up and redundant vacuum circuits were actually correct circuits, but at some point pieces in the circuits were removed.
Hi, Ledzella, if you're still around, would you mind messaging the details of your supplier? I need diagrams for a 78 Country Squire with the 400 (the pictures in the Mitchell's manual are completely unreadable). Pretty sure I'm missing more than a few parts, too.
Thanks!
 
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