My 95 E150 302/E4OD is suffering from myriad symptoms, and I am trying to determine where to start. In my quest to troubleshoot my code 172 (right bank lean) I wanted to make sure that I wasn't dealing with a vacuum leak. I thought that if it was a vac leak, it would throw a left bank lean code as well, but then someone told me it only has 1 O2 sensor?

Anyway, the brake booster hisses. It is not a small hiss either. It changes pitch and intensity based on how much pressure is applied to the brake pedal. If the brake pedal is floored and you increase engine RPM's, the pedal pushes back noticeably (raises), I am guessing due to the lower engine vacuum available. I don't know if that is normal though, I have never noticed it in any of my other non-Ford vehicles. The brakes however, work fine. I searched this topic and came up with a few cases where even a new booster did the same thing, so I am not ready to run out and buy a new booster, but I would like to investigate further. Thanks,

azul

 

Run out & buy another booster. I prefer junkyard parts, but that's just me.

The caption of this diagram explains how the booster works.

 

yep hes right you got a leak in the boster replace

 

when it comes to brake parts i buy new,i guess just peace of mind. anthing else not that picky on

 

I agree on critical parts like calipers, rotors, & pads. But the booster is just a convenience item. Even if it fails, you can still drive safely. And I've never had one fail so suddenly that it was a surprise.

 

up here in massachusetts, the boneyards wont even sell anything brake related,at least the ones in my area