How to check for vacuum leaks? - F150online Forums


How to check for vacuum leaks?

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  #1  
Old 12-26-2006, 04:20 PM
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How to check for vacuum leaks?

How do you check for vacuum leak in the rubber hose for one of the system idle or fuel controls or an intake leak after the throttle body?
I have a 1998 4.6L V8. If oyu have any pics with arrows for what to check that would be great.
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Old 12-26-2006, 05:46 PM
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the scary way is to use carb or brake cleaner and spray lightly around hoses. the safe way is to use a smoke machine to push smoke into the intake while engine is off and it will show you your leak. most likely your leak is the little rubber 90degree elbow behind throttlebody, but i had a broken throttle body elbow bolt that caused mine
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Old 12-26-2006, 05:47 PM
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Spray starting fluid at the hose or area in question. If there is a vacumm leak the engine will start to pick up speed.
bullseye670.............
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Old 12-26-2006, 07:11 PM
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Get a few feet of 1/4" vacuum line. Hold one end to your ear, and pass the other end around by the various fittings and hoses. Works like a stethoscope, doc!
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Old 12-26-2006, 07:26 PM
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If you've got a propane torch, introduce propane slowly around suspect fittings and connections while the engine is running and wait for the engine's idle to change.

Carb cleaner and/or starter fluid works too, just don't spray around plug wires or ignition coils. And if you do...well, your eyebrows do grow back eventually.

The number one suspect area is somewhere in the PCV tube assembly coming off the passenger's side valve cover to the intake manifold.
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Old 12-26-2006, 11:48 PM
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Thanks for all your suggestions i will do that tomorrow and see what i gets me.
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Old 12-27-2006, 11:52 AM
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Pull each line off the source and suck on it. If it does not hold vacuum.. You found the line.
Easy and takes less than five minutes.

Vince
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Old 12-27-2006, 01:23 PM
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What are some of the symptoms of a vacuum leak? I forgot to ask that in thwe beginning.
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Old 12-27-2006, 02:20 PM
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Quote:
Originally Posted by BigRed125
What are some of the symptoms of a vacuum leak? I forgot to ask that in thwe beginning.

PO171, PO174 .

Rough idle..

Air leaking sorta noise

Whistling noise.

Last edited by jbrew; 12-27-2006 at 02:22 PM.
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Old 12-27-2006, 03:43 PM
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Quote:
Originally Posted by jbrew
PO171, PO174 .

Rough idle..

Air leaking sorta noise

Whistling noise.
It doesnt show any codes. But it has a little of a rough idle. Thanks for oyur reply.
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