PROBLEM FOUND...now what??
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Junior User
Joined: Jun 2003
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New Discovery
Hey, thanks for all the help guys, I really do appreciate it. My father and I just went out and did some looking over the Bronc. One thing we checked was the brake booster, seeing as it is one of the major vacuum systems. The engine runs a little rough as it is with minor vibration, but when we pull of the vacuum line running the the booster and plug it with a finger the engine runs grand, smooth as a whistle. Vacuum from the booster runs to the intake close to cylinders 7 & 8, correct? Anyways, before going out and buying a new brake booster I wanted to ask if it would be a wise investment. Thanks again.
Keith
~Houston, TX
Keith
~Houston, TX
Senior User
Joined: Mar 2004
Posts: 497
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From: END OF THE OREGON TRAIL
Sounds like the booster to me. Causing lean misfire. Check the booster to see if it leaks down when vacuum is applied. You'll need a vacuum gauge and a Mityvac to apply vacuum to the booster it should hold vacuum without bleeding down.
I had similar problem on a GMC 454 turned out to be cracked fitting on intake runner to #8 cylinder.
Same symptoms as yours Rough idle and High HC at idle because mixture leans out too much.
Good Luck.
I had similar problem on a GMC 454 turned out to be cracked fitting on intake runner to #8 cylinder.
Same symptoms as yours Rough idle and High HC at idle because mixture leans out too much.
Good Luck.
Senior User
Joined: Dec 2003
Posts: 404
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From: Groton, CT
One other thought, your problem could be caused by the rubber grommet and check valve at the booster. Those grommets get worn out over time and can cause a vacuum leak as well as a crack in the plastic check valve. Not sure how yours is set up, but Autozone has a universal grommet and check valve kit for about 4 bucks.
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