Vaccum piece at back of intake manifold | Ford Explorer Forums - Serious Explorations

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Vaccum piece at back of intake manifold


November 16, 2005
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City, State
Stanardsville, VA
Year, Model & Trim Level
1994 Ford Explorer XLT
So I started the truck today and it started idling real funny... high, low, high, low... then started idling fine... this took place for most of the day today... just popped the hood and found that the vacuum piece at the back of the intake manifold (which has a hose connected to it from the brake booster) appears to be missing a hose? Or at least I do not remember there being an open vacuum line there? Its a small piece with 3 hoses connected to it... and the open metal line has a vacuum line which is just pulling in air from the engine bay? Is that suppose to be there?

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Yes, you are missing a hose and it must be fixed.
There should be an EPA sticker next to the hood latch that provides the vacuum tree layout except for the environmental control and the automatic transmission line.

If you have an automatic transmission, a common problem is a bad modulator that blows the hose off. There is usually some ATF around the vacuum tree.

If you can't find the missing hose, respond and we'll go through the list.

I searched and searched and searched and could not find a missing hose that needed to be connected to the vacuum... I am assuming that this particular intake simply had a cap on it? once I put a metal calve stem cap on it, it started idling perfect... theres no more pressure loss exiting when you shut the car off... I think that I fixed it... I reviewed the under the hood diagram and can not locate where I would be missing a hose? does anyone have pics so that I can be certain? I have the 1994 4 liter V6

Yeah a few of them are capped depending on what options you have. If everything works with the line caped then leave it alone.

Mine was doing the same thing before I replaced the modulator. A couple of times I thought I was missing a cap, but for what ever reason I usually found it under the vehicle or in the drive way when I returned home.Guess I got lucky there. A modulator change seems in order. Its not as hard as you would think, but is rather time consuming and in the end was very well worth the effort. Plus the part is usually around 12 bucks or so

Two of mine are capped also on the bottom, one that would go to the automatic transmission if I had one. The end of a bic pen works in a pinch.
On my 91 there are five hoses
1. A/Cleaner bimetallic
2. Fuel Pressure Regulator
3. Environmental control
4. Brake Booster
5. PCV

If you have an automatic transmission, these are known for blowing off lines when the modulator goes bad. Look for sticky fluid. LXNavajo_94 has good advice if you keep blowing lines off.

Few questions:

anyone have pics?
where is the modulator?
what is the correct item to use to cap the end? do they sell the part at Auto zone?

They sell caps in the "help" section at autopart stores (including autozone).


My tree, there are two capped ports underneath


  • Vacuum Tree.JPG
    Vacuum Tree.JPG
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In looking at the picture posted above from shamaal, everything looks similar except that left hose is the one capped on my vaccum 'octopus'... I will try a search on modulator replacement right now... it sounds complicated?

slow down....

Even with the auto trans there is one or two places on that tree that get capped off.

If you have an auto transmission then you have the vacuum line that runs to teh modulator on the auto transmission, it sounds to me like yours is still hooked up and the truck is running and shifting find now that you capped the vacuum leak, correct?

So what makes you think you need a new modulator in the transmission?
Have you confirmed the vacuum line for the transmission is hooked up?

if you do decide to change the modulator it took me about 2 hours taking my time plus I had just driven thetruck and wanted it to cool down