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1990 XLT with 92-96 Panels, 351W, 3.55L 8.8 Rear, 6" Lift with Idler Arm Steering, 35" Tires
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Discussion Starter · #1 ·
Continuing to go through all of the vacuum lines. Looks like the PCV re-route recommended by Ford (Brake Booster to Rear, PCV to Top) was never done and the PCV still dumps into the rear vacuum port. The brake booster is going into the vacuum tree and not the separate vacuum port on top. Instead, the vacuum port on top is being used by the MAP sensor. Does the map sensor get a better pressure reading by using that solo port?

So here is what I currently have before any changes:
Rear - PCV
Top - MAP Sensor
Tree - Everything else, including brake booster

According to Ford, I believe the brake booster should be moved to the rear. Can anyone confirm this? Also, can the MAP sensor be moved to the tree without degrading the pressure measurements? This seems to be the only way to move the PCV to the top and allow it to vent over the entire manifold. I also don't want the PCV to dump oil into the tree.

I plan to add a catch can to the PCV line before reentering the manifold. I do not have a catch can on the oil breather from the fill neck to the air intake. It vents all the way back to my K&N box and I don't get oil in there. I don't even really foul up the breather filter on the vent line.

I have seen some good posts from @Hillbilly Heaven on catches and PCV, but it looks like a prior tech moved things around and I'm not sure if it makes a difference. Thanks.
 

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1990 XLT with 92-96 Panels, 351W, 3.55L 8.8 Rear, 6" Lift with Idler Arm Steering, 35" Tires
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117 Posts
Discussion Starter · #2 ·
Also, any reason the PCV can't just vent to the air filter box as well? Does it need to be pressurized by the vacuum.
 

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1990 XLT with 92-96 Panels, 351W, 3.55L 8.8 Rear, 6" Lift with Idler Arm Steering, 35" Tires
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Discussion Starter · #4 ·
Thanks. The confusing part was that the PCV hose is a different diameter than the the solo vacuum port on the top. I had to route it to the tree which is where the brake booster was. I just swapped the two of them. Should it be fine to run the PCV to the tree and the brake booster to the back?

Replacing the PCV was one of the most frustrating repairs in recent memory. So simple, yet so little space to maneuver it in there. Thought I was going to have to remove the plenum. It was like doing yoga to angle myself in there. 6" lift and 35s didn't help. :D
 

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Yo Buddy,
Bad headaches here again, sorry! BBL...
Brake Boster vacuum hose is usually larger than 5/32" hard lines; as I believe MAP sensor hoses are larger as well so those two share the top position.
For now:
Rectangle Slope Font Parallel Diagram

Font Parallel Paper Paper product Document

Rectangle Font Parallel Pattern Number
 

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95 f-150 4x4 5.8 e4od 05 F250 axles w/4:10's lifted/modded owned since 97 w/28K
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i re=routed mine to the bottom/middle of the intake plenum, instead of dumping in at the rear for number 8 cylinder. but my edelbrock already had a fitting there so it was simple. now the crankcase vent gets mixed better in the intake instead of constantly being sucked by the rear cylinder.
 
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1990 XLT with 92-96 Panels, 351W, 3.55L 8.8 Rear, 6" Lift with Idler Arm Steering, 35" Tires
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117 Posts
Discussion Starter · #7 · (Edited)
This isn't my plenum, but a picture of the same model. The MAP hose is smaller in my case as pictured. I set it up as labeled.

Automotive tire Tread Terrestrial plant Gas Synthetic rubber
 

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92 Bronco, 408 Stroker, 6R80, 4" lift, 9 inch, ARB lockers, 4.56 gears, Bassani exhaust
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I suggest running it thru a catch can then to the center port.
 

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1990 XLT with 92-96 Panels, 351W, 3.55L 8.8 Rear, 6" Lift with Idler Arm Steering, 35" Tires
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117 Posts
Discussion Starter · #9 ·
@SHOme A catch can is definitely on the list. The fitting on my center port has a different diameter. Do you think it makes a difference between putting it there vs in the main port of the vacuum tree?
 

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92 Bronco, 408 Stroker, 6R80, 4" lift, 9 inch, ARB lockers, 4.56 gears, Bassani exhaust
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I think centered is best IMO. You can get a larger nipple to go in the center. You may even be able to move the tree to the center. I can't remember if the holes were different sizes. If you run a catch can and empty it regularly the amount of sludge will be negligible.
 
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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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The goal of the PCV is right in its name: positive crankcase ventilation. When the crank case sees an overpressure event, the PCV valve opens and shoots oil-laden air into the intake. You want it in the center to distribute that oil to all cylinders instead of just a few.

Vacuum is not a quantitative force. All areas under manifold vacuum will have the same vacuum force. So the MAP can go anywhere in the intake. Preferably not where it will get soaked in oil from the PCV.

Ford put the PCV in the rear of the valve cover. It should be in the front of the valve cover where less oil will pool due to the 3 to 5° rearward tilt of the engine and gravitational forces when driving.

Ideally you will have a catch can on the PCV and the crank case air inlet. The former being more important than the latter.
 

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1990 XLT with 92-96 Panels, 351W, 3.55L 8.8 Rear, 6" Lift with Idler Arm Steering, 35" Tires
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Discussion Starter · #13 ·
@BigBlue 94 Why would you need a catch can on the air inlet? Some sort of back flow? My inlet has a few feet of hose running all the way over to the drivers side wall into the air box with a breather filter on it. Do people see that spitting out oil?
 

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From experience, under sustained high rpm, the inlet will become an extra outlet. This would be the reason to add the catch can there.
Also if you start seeing oil/sludge/emulsion in that can during normal driving it can point to problems, like excessive blow-by. Driving normally most the time, I would expect the air inlet side to be mostly dry, all the time.
 
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85 Bronco, 309ci I6 w/4bbl, np435, 4" lift, 37" Irok NDs, 4.56 w/ Detroit Locker and tru trac
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@BigBlue 94 Why would you need a catch can on the air inlet? Some sort of back flow? My inlet has a few feet of hose running all the way over to the drivers side wall into the air box with a breather filter on it. Do people see that spitting out oil?
Yes, some engines will spit oil out that and soak the filter. As explained by CBG above. Its more of a race car thing, but has a place on some of our truck engines. Especially ones with high milage engines.
 

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My '93 spits oil into the breather box. Bought a new PCV valve, but could never find it on the truck to swap it out.
 

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1990 XLT with 92-96 Panels, 351W, 3.55L 8.8 Rear, 6" Lift with Idler Arm Steering, 35" Tires
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Discussion Starter · #18 ·
could never find it on the truck to swap it out
Check the back passenger side of the valve cover. Mine has a grommet back there with a quick 90 degree bend that then has some tubing going up toward the top of the plenum. My PCV sits at the top of that tubing. It then either goes to the back of the plenum, or wraps around to dump in the middle, which is what my original post was about. Ford recommended moving it.
 

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Figures they'd hide it like that..........
 
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1990 XLT with 92-96 Panels, 351W, 3.55L 8.8 Rear, 6" Lift with Idler Arm Steering, 35" Tires
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Discussion Starter · #20 ·
You want it in the center to distribute that oil to all cylinders instead of just a few.
I ended up leaving it on the tree near the front of the manifold with the idea that the incoming air would drive it back across the rest of the plenum. Much validity to this? Probably just splitting hairs, but figured I'd ask.
 
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