Vacume leak
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Senior User
Joined: Apr 2003
Posts: 270
Likes: 1
From: columbia
Vacume leak
Whenever I drive my 78 F150 custom for about 10 min it acts normal and drives fine but if i drive it longer that that at faster than idle speeds the truck wants to die. When ever the engine
gets abouve idle you can hear a hissing sound and the engine dies but when you release the throttle the engine picks up rpm. Can any one tell me what this is and how to fix it? thanks for any info.
gets abouve idle you can hear a hissing sound and the engine dies but when you release the throttle the engine picks up rpm. Can any one tell me what this is and how to fix it? thanks for any info.
Elder User
Joined: Jan 2004
Posts: 767
Likes: 1
From: Franklin, GA
You probably do have a vacuum leak. Start checking hoses. The bigger ones cause more severe leaks that'll kill the engine pretty easy, like the one going to the brake booster. The booster itself may be the source of the leak too. If you can have it running while you are looking for the source of the hiss, you can use a piece of vacuum line as a make shift stethoscope to locate the noise. Carb base gasket is another place for a leak that will kill the engine easily. EGR valve stuck. Pinch individual vacuum lines closed with your fingers to block off the vacuum and listen for better idle or the elimination of the hiss.
New User
Joined: Oct 2003
Posts: 20
Likes: 0
From: long island
I had a vacuum leak that caused the brakes to ack "funny". It was in the tree at the rear of the intake manifold. It has maybe four lines coming off it and it was a little loose. I screwed it in anothe 1/4 turn and everything is great. good luck !
