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Random Vacuum Hose?

DougO83

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Joined
June 5, 2007
Messages
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City, State
Tomball, TX
Year, Model & Trim Level
1991 Ranger
Ok...My lil Explorer has a rough idle and has a bit of difficulty shifting at times. I was told that both of these could be a vac problem, but I was unable to find anything that looked out of place or was leaking until yesterday. Also, my Check Engine light does not come on.

I found the line in the photo just broken off and I cannot figure out where it goes, so I have two questions:

1. Could this be causing 1 or both problems?

2. Where does this dang hose run?

Thanks Y'all!
Doug

VacuumTree.jpg
 



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Yes, a vacuum leak will cause those problems. The line you are pointing to either goes to the intake box to supply vacuum for the thermostatic element on the heat riser, your HVAC controls on the inside of your explorer, or to the vacuum modulator on your transmission.
 












I forgot to add that it is a 1991 Sport with the 4.0 Push rod. Don't know how much that will change.
 






No, that doesn't change anything. The reason I told you several was because someone could have rerouted the lines in the past. If it is exactly as it should be from the factory, then it should be the line to the transmission modulator. I should have been more clear in my last post, but I didn't want to possibly mislead you and leave you confused if something was changed.

Couldn't it also go to the fuel pressure regulator?

The thin one on the front that bends down should be the one going to the fuel pressure regulator, since it has those bends in it, it shouldn't be anything else. The other ones I can't say because someone may have taken the engine apart in the past and put the vacuum lines back in different locations, but, the one on the back pointing down should be the one to the airbox.

Normally, the one he is pointing at is the line to the transmission vacuum modulator. But, it is possible that it goes to the climate control too. If the vent control is still working, then it is probably the line to the vacuum modulator.
 






Thanks! Once she cools down, I'll poke around and see if that's it.
 






Updated/More accurate Image

Here is an under hood shot of the vacuum tree. The one I posted earlier was not correct. I am still having trouble here and am hoping this might help a little bit.

Thanks!

Doug

SDC12995.jpg
 






You should have the following hoses coming from your vacuum tree.

Brake Booster (which you have identified)
Cruise control (the second largest in the bunch)
Vacuum to the thermostatic control on the airbox for the heat riser.
Transmission Vacuum modulator
Interior HVAC controls
Fuel Pressure Regulator

If they are arranged as they normally are from the factory, the front two should be the cruise control and Fuel pressure regulator. Next, is the brake booster. The last three will be the vacuum modulator, heat riser, and the HVAC controls. I would guess the one on top you have marked unknown is the HVAC controls, follow it to see if it connects to the firewall. As for the other one on top, if it does not go over to the factory air box, and instead dips down behind the back of the engine, it is the line to the vacuum modulator. If everything is using stock lines and the normal placement, then I believe that that should be to your vacuum modulator. Generally speaking, the line for the thermostatic control on the airbox dips below the upper intake manifold next to the vacuum tree, and comes out the other side.

The only other vacuum lines on your engine are from the PCV to the UIM a little ways below the vacuum tree, and the line from your Throttle body to your Vapor canister.
 






I give up. It's nothing. The line is just...there and pulling a significant vacuum through it. I traced every line from the tree and everything listed is connected. I plugged it and am gonna call it a day.
 






The line must go to somewhere. If it is the one to the air box, it separates at the midpoint of the line.

If you don't have both ends of the vacuum line attached, your engine will run poorly, and other devices may not function correctly.
 






The line must go to somewhere. If it is the one to the air box, it separates at the midpoint of the line.

If you don't have both ends of the vacuum line attached, your engine will run poorly, and other devices may not function correctly.

I am just out of ideas for it right now. I thought it might be the A/C one, but it is hooked up and works fine. My HVAC system is working alright except for not being as cool under acceleration. I can't find a loose line on it.

I can't find any hose nipples on the air box or anywhere else. I am going to take some more underhood shots and post them later to see what I am missing. I used to have a 1991 Ranger with the same engine and I never had any trouble, so I never checked on any of these hoses at all.

More to come. Thanks for the help.

doug
 






The hose nipples you are looking for on the air box would be at the top of the air filter box. The vacuum to the HVAC is for the vent controls, not for the heating and cooling itself.
 






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