Brake Booster
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Senior User
Joined: Dec 2006
Posts: 135
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Brake Booster
Will a leaking power brake booster cause gas mileage problems? I have an 88 f150 5.0 When I apply brakes it will sometimes nearly go to the floor and requires a lot of pressure to brake. I bought the truck used and the brakes have never felt right. I replaced rotors pads and shoes and as I stated it brakes fine but takes more pressure than I think it should. I am now wondering if this related to my horrible gas mileage. I have pulled codes and get egr not getting signal, always running lean, and another HEGO(O2 sensor) Problem is if it is always running lean why am I getting 9-10 mpg no matter how I drive. My thought is if the booster is bad would that not cause a lean condition(vacuum leak) which in turn would cause the ecu to continually read a lean condition and dump more fuel? The truck has stock wheels/tires. No gas leaks. Good compression. Timing is right on. As I say I get 10 or less mpg. It does not matter if I am hauling a full load or driving down hill. Any thoughts? Thanks
Fleet Mechanic
Joined: Mar 2005
Posts: 1,603
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From: St Louis
Sounds like you have multiple problems related to the brake booster (excessive force on brake pedal for braking) and a leaking master cylinder (occasional sinking brake break pedal)/or leaking slave at one of the wheels. If your booster is bad it could cause the vacuum leak to make a lean condition. I would also check your other vacuum lines carefully, no matter how hard they are to get at for a visual inspection.
Check your line from the engine to the booster and see if it is hard or split anywhere. It can cause the vacuum leak to the booster as well.
Check your line from the engine to the booster and see if it is hard or split anywhere. It can cause the vacuum leak to the booster as well.
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Senior User
Joined: Dec 2006
Posts: 135
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I have no leaks at the master nor at the wheels. Also no vacuum leaks. I can pull the line from the booster and when I block it off I get a slightly lower idle. I also get a change in idle when I depress the brake. Question still remains would a leaking booster cause the ecu to send more fuel trying to make up for the lean condition?
