Does anyone know where the EGR's vacuum line plugs in?  I read in the FSM that it plugs into the throttle body's ported vacuum port but then it notes that the only thing that is plugged in there is the T connector that comes from the dizzy & charcoal canister...

 

Any ideas?

I had to plug that hose when I deleted the egr stuff so I'm gonna say that's it.

Vacuum diagram

 

Does the OEM throttle body have 2 ported vacuum ports?  I have the weber big-throat one and it only has one port so I was considering using 2 T-connectors to hook the carbon canister, distributor and EGR to the same port, would that work?

I haven't a clue. I plugged the hose under the TPS circled in yellow to get my car to run after removing egr crap. I don't remember it having anything to do with the distributor or canister? Seems like one of the two hoses off the egr went there and the other to that thermal vacuum switch on the warming plate. It's been a long time and I've forgotten, sorry.

Edited May 15, 20213 yr by siteunseen

30 minutes ago, siteunseen said:

I haven't a clue. I plugged the hose under the TPS circled in yellow to get my car to run after removing egr crap. I don't remember it having anything to do with the distributor or canister? Seems like one of the two hoses off the egr went there and the other to that thermal vacuum switch on the warming plate. It's been a long time and I've forgotten, sorry.

Gotcha - where did you hook up your distributor's vacuum advance pod?

I'll have to get a picture. Give me an hour, not near the car at the moment.

1 hour ago, chaseincats said:

Gotcha - where did you hook up your distributor's vacuum advance pod?

Okay...

There's one on the driver's side that went to the egr. In my pic above circled in yellow.

The one you're talking about is on the passenger's side of the throttle body and goes the vacuum advance dashpot and the canister.

Here's where it connects to the throttle body...

Here's the T...

Canister connection...

I can do better later. I'm helping my neighbor right now so let me know if you want better. Cliff

Thanks for the pictures, so the OEM throttlebody does seem to have two inlets

Here's a decent pic showing both.

Your idea of T ing off one should work. 2 Ts and some hose. That sounds good. I like hoes.

 

As Site mentioned above, the original throttle body has two ported vacuum sources. One for the EGR and the other shared by both the carbon can and the distributor vacuum. Here's another pic showing the two vacuum nipples:

And about the idea of sharing the same ported source for all three things (distributor, EGR, and vacuum can), it'll "work", but you can tell from the placement and size of the original vacuum holes that Datsun wanted different vacuum profiles for the two different ports.

Here's a pic down inside the throat of the original throttle body. The three small holes in the back are for the ported vacuum sources. (The two larger holes in the foreground are for the BCDD). The narrow slit hole on the left is for the distributor and CARB can. And the pair of holes on the right are for the EGR. You can see by looking at the shape, size, and position of the holes, that they will have different vacuum profiles at different pedal positions. Looks like this:

So I'm thinking that it'll "work", but the vacuum profiles won't be the same as stock. Then again... Who's to say that your one ported vacuum source is the same as either stock port anyway?   

15 hours ago, Captain Obvious said:

As Site mentioned above, the original throttle body has two ported vacuum sources. One for the EGR and the other shared by both the carbon can and the distributor vacuum. Here's another pic showing the two vacuum nipples:

And about the idea of sharing the same ported source for all three things (distributor, EGR, and vacuum can), it'll "work", but you can tell from the placement and size of the original vacuum holes that Datsun wanted different vacuum profiles for the two different ports.

Here's a pic down inside the throat of the original throttle body. The three small holes in the back are for the ported vacuum sources. (The two larger holes in the foreground are for the BCDD). The narrow slit hole on the left is for the distributor and CARB can. And the pair of holes on the right are for the EGR. You can see by looking at the shape, size, and position of the holes, that they will have different vacuum profiles at different pedal positions. Looks like this:

So I'm thinking that it'll "work", but the vacuum profiles won't be the same as stock. Then again... Who's to say that your one ported vacuum source is the same as either stock port anyway?   

Interesting I had no idea there was a size differential.  I did take it out last night with everything connected and did notice the car was a little bit more sluggish, I'm assuming that's mostly due to EGR and not the carb canister?  I had the canister hooked up for a while before I discovered it had a small vacuum leak.

I think that the shape of the hole(s) are also as important as the sizes.

For example, if I theorize way above my pay grade, I would imagine the shape of the distributor advance goes like this... They wanted a very narrow spike of vacuum oat a specific pedal position, so they used a narrow slit. And I can affirm (from driving around with a vacuum gauge T'd into that line) that the vacuum spike is very narrow and very high (vacuum).

The EGR ports on the other hand, appear to be placed to provide vacuum over a much broader pedal position. I'm guessing the smaller hole in the back is used to "extend" the EGR vacuum value deeper into the throttle.

So my read on the whole thing is... They optimized the ignition advance to kick in only at one narrow pedal position (light cruise), but the EGR is activated over a broader range and deeper into the pedal (medium cruise).

But, neither of those ports will produce any significant vacuum once you get above medium cruise.