SCREAMING vacuum leak???

[DesertDoc]

I'm getting this high pitched whistle/whine/noise after the engine warms up while driving. Did I mention that it was loud! It changes pitch with the throttle and disappears under load, as when accelerating and getting up to speed. It's present during idle and try as I might I can't seem to locate it. It seems to be coming from the passenger side of the engine towards the front. It's not the alternator or smog pump, I've already replaced the alternator recently and isolated the smog pump....ANY IDEAS were to look next. I've tried spraying WD40 on the lines and hoses that I can get to...but no joy. Though....when I thought it was the belts (which have all been replaced) and sprayed belt dressing did seem to stop it for a very short (measured in minutes) while. I've noticed some Ported Vacuum Switches that are located to the driver's side at the rear of the engine. There are some small stiff hoses that come off the switches one cracked (due to time I guess) and there's a black one that comes out of a bundle at the front of the engine that is broken off and I can't find where the other half of it is or goes to.

QUESTION:

1. Has anyone had a simular problem like this and how did you fix it?

2. How can I find the leak?

3. Where can I get replacement tubes/hoses for the vacuum switches?

4. Where does that black tube go?

5. Are there any diagrams of the vacuum system for an '85 4.9L six? My Haynes Repair Manual is worthless on this...as is Chiltons.

Thanks

 

[Seabronc]

I'm getting this high pitched whistle/whine/noise after the engine warms up while driving. Did I mention that it was loud! It changes pitch with the throttle and disappears under load, as when accelerating and getting up to speed. It's present during idle and try as I might I can't seem to locate it. It seems to be coming from the passenger side of the engine towards the front. It's not the alternator or smog pump, I've already replaced the alternator recently and isolated the smog pump....ANY IDEAS were to look next. I've tried spraying WD40 on the lines and hoses that I can get to...but no joy. Though....when I thought it was the belts (which have all been replaced) and sprayed belt dressing did seem to stop it for a very short (measured in minutes) while. I've noticed some Ported Vacuum Switches that are located to the driver's side at the rear of the engine. There are some small stiff hoses that come off the switches one cracked (due to time I guess) and there's a black one that comes out of a bundle at the front of the engine that is broken off and I can't find where the other half of it is or goes to.
QUESTION:

1. Has anyone had a simular problem like this and how did you fix it?

2. How can I find the leak?

3. Where can I get replacement tubes/hoses for the vacuum switches?

4. Where does that black tube go?

5. Are there any diagrams of the vacuum system for an '85 4.9L six? My Haynes Repair Manual is worthless on this...as is Chiltons.

Thanks

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You can use propane to find the leak. Take a propane torch and crack the valve to allow a light flow of gas. The move the tip around the vacuum system. When the engine speeds up you are at the lek. A common place other than a bad vacuum line is the base of the carborator.

There is a complete vacuum diagram located on the right side of the radiator support. Each function is color coded.

Green = EGR function

Orange = heat control valves (AKA heat riser function)

Red = Main vacuum (supply)

Yellow = spark advance

Pink = Thermactor control

Blue = Throttle kicker (A/C)

White = EGR supply

Black = usually Evaporative emissions control

Black = sometimes misic function

Here is a 86 4.9 L diagram, probably similar to yours.