Vacuum Leak
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Junior User
Joined: Aug 2006
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Vacuum Leak
My 69 F-100 has been running very rough at idle lately. In asking around it sounds like a vacuum leak. I've never worked on cars but since owning this truck a few years ago I've learned to do many things myself. I've read that I should buy some carb cleaner and spray around the hoses near the intake manifold. I have a 302 V-8 with auto transmission. How many hoses should I be looking for and are they all the small 1/4" or so hoses?
Also, will a vacuum gauge tell you that you definetly have a vacuum leak. And help and tips are greatly appreciated from this neophyte.
Also, will a vacuum gauge tell you that you definetly have a vacuum leak. And help and tips are greatly appreciated from this neophyte.
Cranky Old Guy
Joined: Mar 2008
Posts: 3,562
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From: Raphine, Virginia
Vacuum reading is going to depend on condition of your engine generally. Exceptions include cam grind. But very useful in trouble shooting and tuning. Worth every penney. It will tell you when you fix a leak. Gaskets on carb base, intake gasket etc you can find with the carb cleaner. Hose is cheap, replace them if any doubt. A lot of times they get loose at the fitting and you can cut back a half inch and reuse. Most lines are the small ones, exception being Power brake booster which could also be leaking internally and the PCV hose's. Don't forget the vac line going to the tranny modulator. That'll get you started.
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Junior User
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There is a small rubber hose coming out of the side of the tranny and it looks like it runs into the firewall behind the dashboard. I noticed that there are three cracks in this line but when I sprayed carb cleaner on the cracks it did not change the idle speed or anything.
Posting Guru
Joined: Aug 2005
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There is a small rubber hose coming out of the side of the tranny and it looks like it runs into the firewall behind the dashboard. I noticed that there are three cracks in this line but when I sprayed carb cleaner on the cracks it did not change the idle speed or anything.
. I'll check on the right side. Thanks.
