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Engine - General, Exhaust & Induction Topics about the general engine items, exhaust system discussed here & Improving the intake tract - air filter to intake valve.

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post #1 of 12 Old 08-09-2019, 10:07 AM Thread Starter
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52 MM TB vacuum question

Im installing a 52mm TB on my T2. The stock TB has 2 Vac ports, obviously one is ported and the other is manifold vacuum. However, the 52 mm that I have only has one vacuum port. It looks like its manifold vacuum only. If I install both the charcoal canister lines to that one port, using a vacuum tee, will that throw a C/E light or give problems? The canister will now be running on manifold vacuum only instead of manifold AND ported vacuum like the stock setup. thanks
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post #2 of 12 Old 08-10-2019, 08:14 AM
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Re: 52 MM TB vacuum question

Both lines from the TB ports run to the same line.

Not exactly sure what they are trying to accomplish with this vacuum setup other than they do not want the canister to purge at idle.

Remove the line from the canister, is there vacuum present at idle with the stock TB?
Is there vacuum present when you open the throttle?
Install the new TB and connect both lines to the single port and repeat.
What were the differences?

Connected/disconnected, either way this will not cause the CEL to illuminate, OBD1 only knows if the purge solenoid is functioning electrically, it knows nothing about vacuum routing or leaks/restrictions in the evap system.

52 MM TB vacuum question-89-turbo-2-vacuum.jpg

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post #3 of 12 Old 08-10-2019, 01:23 PM Thread Starter
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Re: 52 MM TB vacuum question

i know improbably wrong, but since vacuum is highest at or near idle, wouldn't that canister purge at idle and NOT while the motor is under load? Either way, I will do what you said and see the results. thanks alot
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post #4 of 12 Old 08-11-2019, 11:11 AM
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Re: 52 MM TB vacuum question

you need a 52mm from a 3.3 V6, not the 3.0V6. The 3.3 has the same ports as the turbo cars.
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post #5 of 12 Old 08-12-2019, 09:10 AM
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Re: 52 MM TB vacuum question

Quote:
Originally Posted by Moparkid2.2 View Post
i know improbably wrong, but since vacuum is highest at or near idle, wouldn't that canister purge at idle and NOT while the motor is under load? Either way, I will do what you said and see the results. thanks a lot



As it turns out...
I, I, I was wwwwwroooong.


I still have no idea why the two lines are run together, been over thirty years since I had "principal and theory" on these cars.

52 MM TB vacuum question-evap-system-1.jpg

52 MM TB vacuum question-evap-system-2.jpg

52 MM TB vacuum question-air-90-throttle-body.jpg
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post #6 of 12 Old 08-12-2019, 09:25 AM Thread Starter
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Re: 52 MM TB vacuum question

NAJ... You are still the man, the myth and the legend. thank you sir
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post #7 of 12 Old 08-12-2019, 01:22 PM
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Re: 52 MM TB vacuum question

One nipple is before the throttle plate, the other is after, so on closed throttle there is momentary pressure differential. I thought both were the same source (well they are kinda sorta). I figured this out recently messing with my BOV set-up - if it helps at all with this. On the 2.2T/2.5T the large nipple is after the throttle plate (manifold side)
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post #8 of 12 Old 08-12-2019, 04:26 PM
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Re: 52 MM TB vacuum question

Quote:
Originally Posted by NAJ View Post




I still have no idea why the two lines are run together, been over thirty years since I had "principal and theory" on these cars.

I do! The big nipple in the middle is ported vacuum. So it'll suck air when the little one is seeing boost.

http://www.thedodgegarage.com/turbo/turbo189.jpg

The check valves keep boost from backing up the system.

Quote:
Originally Posted by yellonoma View Post
One nipple is before the throttle plate, the other is after, so on closed throttle there is momentary pressure differential. I thought both were the same source (well they are kinda sorta). I figured this out recently messing with my BOV set-up - if it helps at all with this. On the 2.2T/2.5T the large nipple is after the throttle plate (manifold side)

Backwards. The large nipple in the middle is before the throttle plate and is ported vacuum. The small nipple on the drivers side of the TB is behind the throttle plate and gives you pretty much the same signal that the rest of the intake sees.
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post #9 of 12 Old 08-13-2019, 08:30 AM
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Re: 52 MM TB vacuum question

Quote:
Originally Posted by GLHNSLHT2 View Post
Backwards. The large nipple in the middle is before the throttle plate and is ported vacuum. The small nipple on the drivers side of the TB is behind the throttle plate and gives you pretty much the same signal that the rest of the intake sees.
Thanks for clarifying, I screwed that one up!
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post #10 of 12 Old 08-13-2019, 08:45 AM
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Re: 52 MM TB vacuum question

Quote:
Originally Posted by GLHNSLHT2 View Post
I do! The big nipple in the middle is ported vacuum. So it'll suck air when the little one is seeing boost.

http://www.thedodgegarage.com/turbo/turbo189.jpg

The check valves keep boost from backing up the system.




Backwards. The large nipple in the middle is before the throttle plate and is ported vacuum. The small nipple on the drivers side of the TB is behind the throttle plate and gives you pretty much the same signal that the rest of the intake sees.

I am going to agree to disagree...

I understand the difference between ported and straight manifold vacuum, ported has always been used when they do not want vacuum @ idle.
Extremely common on carburated cars that used a PVS for say EGR control and they did not want any vacuum at idle.
In this case once the throttle opens enough to uncover the ported port then both ports are providing the same vacuum, the vacuum in each line which becomes one line does not increase with both ports open and if manifold vacuum drops while the throttle is opened both ports decrease as long as the ported port is uncovered.
It seems to be redundant or a "failsafe"...
If you have 18"HG @ idle on the canister from manifold vacuum that will not increase if you uncover the ported port, 18" HG from one port or two ports running to the same line still = 18"HG.

Also...
If the throttle is opened both ports (ported and manifold) are and will be exposed to the same exact conditions that are present in the manifold.
Once the ported port is uncovered it then becomes manifold vacuum.
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post #11 of 12 Old 08-13-2019, 09:00 AM Thread Starter
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Re: 52 MM TB vacuum question

ok yes. now my other question. DOES ANYONE HAVE A 52mm WITH BOTH VACUUM PORTS FOR SALE? LOL i dont want to run into problems with using a single vac port 52mm.
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post #12 of 12 Old 08-14-2019, 11:55 AM
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Re: 52 MM TB vacuum question

I have a 52 I could sell you. Normally little one goes to BOV and we plug the larger one. Also as many know stock replacement adjustments the throttle is adjusted for a V6. So remember to plug any larger AIS hole and unplug the manual adjust screw and adjust the idle warm mechanically at 950. Then hook up the AIS to have the idle right. Bouncing RPM is a good sign you're not adjusted right.
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