Engine Vacuum question

Yoyoda

Member
Mar 4, 2014
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Ontario Canada
The Corral couldn't help me, so I'm hoping Stangnet comes to the rescue.
I’m switching to an Explorer intake on my current engine build. In my current configuration I only run PCV and Evap from the front side of the manifold. Brake booster, EGR and FPR off the rear of the manifold with the bigger tube going to the brake booster.
On the Explorer upper I have, I’m ok on the front, but it only has one large tube and one small tube in the rear.
Question is: will I have enough vacuum running EGR and FPR both off that one little tube with a vacuum tee?
Alternatively I could run the big tube to a foxbody plastic tree and run everything off that, but I’m trying to keep it as tidy as possible. Not a lot off room in the engine bay. I may eventually ditch EGR so would prefer to not add another barb to the manifold if possible.
Also had considered drilling and tapping for the OEM branch, but the lower part of the Explorer plenum is much wider than the HO plenum so the tubes would end up sticking out the back too far. Again not much room in the Miata engine bay.
I can post pics later if that's helpful.
Cheers.
 
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jrichker

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The Corral couldn't help me, so I'm hoping Stangnet comes to the rescue.
I’m switching to an Explorer intake on my current engine build. In my current configuration I only run PCV and Evap from the front side of the manifold. Brake booster, EGR and FPR off the rear of the manifold with the bigger tube going to the brake booster.
On the Explorer upper I have, I’m ok on the front, but it only has one large tube and one small tube in the rear.
Question is: will I have enough vacuum running EGR and FPR both off that one little tube with a vacuum tee?
Alternatively I could run the big tube to a foxbody plastic tree and run everything off that, but I’m trying to keep it as tidy as possible. Not a lot off room in the engine bay. I may eventually ditch EGR so would prefer to not add another barb to the manifold if possible.
Also had considered drilling and tapping for the OEM branch, but the lower part of the Explorer plenum is much wider than the HO plenum so the tubes would end up sticking out the back too far. Again not much room in the Miata engine bay.
I can post pics later if that's helpful.
Cheers.
Vacuum is the same on every vacuum port of an EFI engine.

Having said that, the fuel pressure regulator should have it own dedicated vacuum connection that isn't shared with anything else. Changes in the vacuum due to the operation of some other system on the same vacuum line can create a difficult to diagnose engine problem. This is due to changes in vacuum at the fuel pressure regulator when the other system like power brakes or HVAC is operated. Squirrely fluctuations in vacuum and the resulting change in air/fuel ratio could be very difficult to diagnose.

If the fuel pressure regulator develops an internal leak into the vacuum side, gasoline can travel to whatever is in the same vacuum line. Use the HVAC vacuum line and fuel leaking from the regulator can get into the HVAC controls and mess them up. The same thing is true if the fuel pump regulator is connected to the power brake vacuum. Fuel in the power brake line will probably destroy the brake booster pretty quickly.
 
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Mustang5L5

i'm familiar with penetration
Mod Dude
Feb 18, 2001
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FPR and charcoal canister need their own dedicated vac lines due to possible fuel intake. If this is a speed density car, you also want dedicated vacuum for the MAP sensor.

You can pull the explorer vac lines and drill/tap to install the mustang vacuum tree.

I pulled and drilled/tapped npt to hose bare fittings for the standard mustang HO setup

6AB1AC10-9D3C-4B59-BF7F-6A38559DE3F2.jpeg
 

Yoyoda

Member
Mar 4, 2014
22
3
14
Ontario Canada
Thanks. Yes I considered tapping for the vacuum branch, but couldn't because it ends up being too far back. My heads are nearly touching the firewall in this conversion. Parts are currently out for powdercoating, so I'll probably end up getting the little plastic tree to run brakes and EGR off of, the FPR can use the little tube off the rear of the plenum, and Evap can run off the little tube in the front with PCV run as shown in your pic.
Thanks all.